Preparation and conformational studies of chiral camphor-derived oxaziridines

摘要

J. CHEM. SOC. PERKIN TRANS. 1 1990 Preparation and Conformational Studies of Chiral Camphor-derived Oxazi rid ines Uwe Verfurth and Rudolf Herrmann* Organisch- Chemisches lnstitut der Technischen Universitat Munchen, Lichtenbergstr. 4, 0-8046 Garching,FRG The syntheses and properties of new chiral N-sulphonyloxaziridines based on (-) -(camphorsulphonyl) -imine modified in position 3 of the camphor skeleton are reported. The preferred conformations of the 3-spiro-acetals and -thioacetals have been studied by NOE measurements. Chiral N-sulphonyloxaziridinesI have been introduced as enantioselective oxidizing agents for many compounds, e.g. sulphides 2p and car bani on^.^ The resulting chiral sulphoxides or a-hydroxy esters are useful starting materials for the synthesis of many naturally occurring compound^.^ Of particular interest are such oxaziridines which can be derived from readily available materials from the chiral pool with a rigid structure, thus reducing the problem of separation of isomers during the synthesis.The camphor-derived oxaziridines (1H6)are of this and often lead to quite enantioselective reactions, but other modifications of the principal structure are still of considerable interest for further improvement of these chiral oxidants. In this paper, we report on the synthesis of such com- pounds with structural modifications in position 3 of cam- phor, and on their conformations in solution, which can be expected to give valuable hints on their ability for asymmetric oxidation.amp;:so,;;/ 0 Results and Discussion Synthesis.-The synthesis of the oxaziridines from the (-)-(camphorsulphony1)imine(12), which is readily prepared from (1 S)-(+)-camphor-8-sulphonic acid and is also commercially available, is straightforward and outlined in the Scheme. The bromination of (-)-(camphorsulphony1)imine (12) leads to an exolendo-mixture of 3-bromo(camphorsulphonyl)imines(8) and (9) in the ratio ca. 3:7. Further bromination gives the 3,3-dibromo(camphorsulphonyl)imine (10) which, however, could not be oxidized to the oxaziridine, presumably because of steric reasons. Although it may be possible to separate the exo-and endo-isomers (8)and (9) by crystallization,' we found it more convenient to explore the different reactivity of the two isomers towards 3-chloroperbenzoic acid (MCPBA). Thus, at low concentrations of all reactants, a clean oxidation of the exo- isomer (8) occurs, leaving the endo-compound (9) almost unchanged.The exo-3-bromospiro-oxaziridine(7) is difficult to separate from the endo-imine (8), but can be identified by its NMR spectrum, and was used for oxidation without separation. It shows a much higher reactivity towards reducing agents like sulphite, and from oxidations with high concentrations of all reactands and a higher excess of MCPBA, where both imines are oxidized, the endo-3-bromospiro-oxaziridine (13) can be obtained in pure state by destruction of the exo-oxaziridine (7) by several rapid washes of a dichloromethane solution with sodium hydrogen sulphite.Chlorination of the endo-3-bromo imine (9) leads to the (3S)-imine (14), and excess of chlorine forms the dichloro imine (11) from the imine (12).' The oxidation of these chlorinated imines to the corresponding oxaziridines by a large excess of MCPBA is possible, but occurs with very low yield, and we found it difficult to separate the oxaziridines from the starting materials. They are therefore not further considered here. Oxidation of compound (12)with selenium dioxide leads to (3-oxocamphorsulphonyl)imine (16),3and the new carbonyl group allows for further modifications of the general structure. It readily forms acetals and thioacetals with alcohols and thiols, such as the simple acetals (15), or the spiro compounds (17), (19), and (20) with diols and dithiols.Surprisingly, we found it impossible to oxidize the simple acetals (15) with MCPBA; the difficulties in the oxidation of the sterically more hindered imine (19) are easier to explain. However, the spiro acetals (17) and the spiro thioacetals (20) readily react with MCPBA to form the oxaziridines (18) and (24); for the thioacetals, a large excess of MCPBA is necessary, as the sulphur atoms are oxidized first, forming mixed sulphoxide-sulphone compounds as intermediates. The introduction of the last oxygen at one of the sulphur atoms, however, is the most difficult step in this oxidation; for the five-membered ring (n = 2), only a mixture of three oxaziridines could be obtained, one of them being the fully oxidized compound (24a), according to mass spectral analysis, while the other oxaziridines are probably a mixture of the isomeric mixed sulphoxide-sulphones.The oxidation is cleaner with the six-membered thioacetal (n = 3). The pure disulphone-imines (21) can be obtained by oxidation of compounds (20)with hydrogen peroxide, and we found it 2920 J. CHEM. SOC. PERKIN TRANS. 1 1990 v R' = Br, R2 = H (8) R' = H, R2= Br (9) R' = R2 = Br (10) R' = R2 = CI (11) R' = R~=H (12) R'=CI, R2=Br (14) V R = Me (ISa) R = Et (15b) V 0 ii-1 bsol;jiv X=CI (22a) X = Br (22b) iii/ R'=Br, R2= H (7) R' = H, R2= Br (13) V e0N n so2 n =2 (17a) n =3 (17b) n =2 (18a) n =3 (18b) n =2 (20a) n =2 (21a) n =3 (20b) n =3 (21b) iiibsol; V n =2 (24a) n = 3 (24b) V Xexso2 '0 X= CI (23a) X = Br (23b) Scheme.Reugenfsundcondifions:i, HC(OR),, Amberlyst 15,CH2C12; ii, diol, toluene, PTSA, 100 OC;iii, MCPBA, CH2C12-aq. Na,CO,; iv, PPh,, CX,, CH,CI,; v, dithiol, BF,*Et,O, toluene, 100 OC; vi, H202,AcOH, 90 "C. impossible to convert compounds (20)into the corresponding oxaziridines with MCPBA. Finally, we found that the carbonyl function of compound (16) is readily converted into the dihalogenoalkene in the exocyclic olefins (22), a very clean reaction which has been described only for aldehyde^,^ and that the imines thus formed can be oxidized to the oxaziridines (23)with MCPBA, without attack at the C=Cdouble bond.It is interesting to note that all camphor-derived imines are oxidized to a single diastereoisomer of the corresponding oxaziridine; the bulky methyl groups efficiently shield the exo side and allow the approach of the peracid exclusively from the endo direction. The resulting oxaziridines thus have a definite configuration with an endo oxygen.'.'' Conformational Studies.-The efficiency of oxaziridines as chiral oxidants can be expected to depend strongly on both configuration and conformation, in particular in the region close to the oxaziridine ring. For example, it was found that compounds (1) and (3)form different enantiomers of methyl phenyl sulphoxide upon the oxidation of the corresponding ~ulphide,~a result which is probably due to steric factors.The J. CHEM. SOC. PERKIN TRANS. 1 1990 292 1 Table 1. 13C NMR (90.56 MHz) data of imines and oxaziridines; amp;values in CDCl, if not otherwise specified. Carbon(s) ~ Compound 1 2 3 4 7 8 9, 10 11,12 13 54.1 100.0 44.5 54.1 21.8,27.9 44.2 49.6 20.4, 22.3 64.3 191.2 53.2 42.3 26.8,27.8 49.0 50.0 20.0,20.6 63.4 190.4 50.6 48.1 21.9,28.3 44.8 50.5 18.6, 20.2 63.8 190.3 53.0 61.6 27.3,28.7 47.9 51.2 22.8,22.9 64.2 189.2 82.0 61.3 25.1, 27.4 47.9 50.8 21.6,21.7 54.5 195.6 35.6 44.3 26.3, 28.1 47.9 49.1 18.7, 19.1 54.5 96.1 44.5 54.1 21.8,28.0 47.1 49.6 20.2,22.2 63.9 189.5 66.7 61.7 25.2,27.4 47.9 51.1 22.5, 21.9 64.3 198.1 103.1 52.3 20.8,29.4 46.0 49.1 20.6,20.7 50.4,50.7 64.2 189.2 102.5 52.7 20.8,29.5 45.9 49.2 20.7,20.8 58.6, 58.7 15.0, 15.1 63.8 192.2 107.9 52.8 20.6,28.5 45.2 48.9 19.2, 19.9 63.9,65.8 65.5 188.5 99.5 56.3 19.4,29.6 45.6 48.1 20.4, 20.7 61.8, 62.9 25.3 54.1 99.2 108.6 54.3 20.9,28.0 45.2 48.4 19.6,21.6 64.5,66.3 55.0 98.4 99.5 55.0 19.5,28.1 45.0 47.3 20.4,21.8 62.2,62.6 24.6 65.7 188.3 99.5 56.1 19.6,29.5 45.8 48.3 20.3,20.7, 72.2,73.3 30.36 21.6,22.6" 65.0 198.8 66.7 57.2 27.5,28.7 48.2 50.2 20.1,21.2 41.4, 57.3 65.8 193.8 49.8 56.9 28.4 48.9 48.8 21.7,22.7 22.2,22.7,24.4 65.5 183.8 81.5 52.3 21.3,27.9 48.7 52.5 18.9, 19.2 48.7,49.6 65.4 183.8 94.6 52.9 22.6,28.2 49.4 46.2 19.5,21.3 48.8,49.3 14.2 65.3 181.9 129.9 54.3 25.0,28.7 48.3 49.1 18.7, 19.6 134.8 65.7 182.8 99.6 57.4 24.5,28.4 48.6 49.3 19.3, 19.8 141.2 55.2 93.9 123.4 54.9 24.9,28.2 46.8 47.8 17.8,20.9 133.7 57.6 94.4 100.1 58.1 24.4,28.4 46.3 47.9 19.3,22.0 139.3 55.2 99.5 98.5 55.3 24.5,28.1 45.0 47.2 20.3,21.8 62.2,62.6 19.4 " Methyl groups of camphor and acetal ring not separated.Spectrum in (CD,),SO. principally rigid structure of the bicycloC2.2. llheptane skeleton The assignment of the protons at the carbon atoms C-5 and does not allow for much conformational variation, and thus its C-6 as exo or endo is based on the absence of coupling between simple derivatives can be judged on their configuration alone. the bridgehead hydrogen 4-H and the exo-5-H, due to a The formation of spiro acetals and thioacetals, in particular similar dihedral angle between these atoms in all cases, which those with six-membered rings, introduces new conformational leads to a coupling constant of ca.zero; on the other hand, a very flexibility, and we therefore thought it worthwhile to study strong NOE effect between these hydrogens indicates their close their behaviour in solution. For comparison, we also include an proximity. The endo-5-H shows a coupling to 4-H of ca. 4 Hz in analysis of the corresponding imines. almost all cases, which confirms the general rigidity and The general assignment of the 13C signals is based on DEPT similarity of the camphor moieties. In well resolved systems, the spectra and, in some cases, C-H correlation,'2 and are given combination of coupling and NOE measurements allows us to in Table 1.identify em-and endo-6-H as well. The geminal hydrogens at C- For 'H NMR spectra, the combination of COSY and 8 always appear as a pair of doublets with coupling constants ROESY ' (measurement of nuclear Overhauser enhancement of 12-14 Hz, as in almost all derivatives of camphorsulphonic in the rotating frame) allowed both configurational and acid; the rigidity of the heterocyclic ring fixes the hydrogens in conformational assignment of the corresponding protons in upward (em) and downward (endo) positions, and the em-8-many cases, and only for situations of severe overlap did some H can be assigned due to its stronger NOE effect with the doubts remain. Interestingly, there is a strong dependence of methyl groups.These groups can also be distinguished by chemical shifts and NOE effects on the solvent (e.g. CDC13 us. their NOE effects with 5-H and 6-H; the methyl group anti to C2H6acetone), which means that its influence on the con- the substituted C,-bridge (10-H3) has a medium NOE effect formations and thus the efficiency in enantioselective oxid- with 5-H and 6-H, while there is almost none with the syn ations may be considerable. The results for imines are sum- methyl group (9-H,). marized in Table 2, and for oxaziridines in Table 3. As no NMR In the cyclic acetals and thioacetals, no NOE effects are found data have been reported up to now for some of the halogenated between the camphor system and the heterocyclic ring, which imines, which have been known for almost 90 years, these are means that there exists a general tendency in these spiro also included.compounds to minimize steric strain by directing this ring away The chemical shifts follow the patterns observed for other from the camphor moiety. In the five-membered ring systems, bicyclohexane~.'~The transition from an sp2 carbon to an sp3 the NOE effects between all hydrogens of the heterocycle are of carbon in the oxidation of the imine to the oxaziridine is similar strength, which can be expected for such rigid systems. associated with an upfield shift of this carbon of ca. 90 ppm; the The six-membered rings allow for more flexibility, and several normal range for the imines is Sc 180-200, while the oxaziridines conformations of high relative stability are conceivable; there show the corresponding signals between tic 9amp;100.There is also exist many examples for non-chair conformations (boat and an upfield shift of the 'H NMR signals of hydrogens not too far twist forms) in heterocyclic rings.I6 In such rings not connected away from the site of the oxidation; the effect is best seen in the to other cycles, rapid equilibrations of the different conforma- bridgehead hydrogen 4-H (AS 0.4 ppm). The 13C chemical tions are observed, and only at quite low temperatures is this shifts of the acetals, thioacetals, and disulphone rings are as process slowed down sufficiently for direct observation by expected.' NMR techniques in the case of dioxanes and dithianes; Table 2.H NMR spectra (360 MHz) of (camphorsulphony1)imines; amp;values (multiplicity, J-values in parentheses). Atom(s) Com-pound Solvent 3 4 5 6 8 9, 10 11,12 13 CDCI, 4.68 (s) 2.50 (d, 4.6 Hz) 1.53 (1 H, rn), 1.71 (1 H, m), 1.98 3.10, 3.25 (both d, 13.5 Hz) 1.10, 1.37 (2 H,m) CDCI, 4.90 (d, 4.2 Hz) 2.38 (tr, 4.2 Hz) 1.70 (1 H, m), 2.00 (2 H, m), 2.20 3.00, 3.25 (both d, 13.3 Hz) 0.88, 1.57 (1 H,m) CDCl, 2.90 (d, 4.2 Hz) 1.90,2.02,2.17,2.43 (all 1 H, m) 3.21, 3.39 (both d, 13.6 Hz) 1.24, 1.28 CDCI, 2.80 (d, 3.7 Hz) 1.84 (1 H, m), 2.13 (2 H, m), 2.38 3.23, 3.41 (both d, 13.6 Hz) 1.18, 1.23 (1 H,m)CDC13 2.32(d, 19.3 Hz, 2.19 (t, 4.0 Hz) 1.42 (1 H, m), 1.67 (1 H, m), 2.02 2.92, 3.14 (both d, 14.3 Hz) 0.90, 1.03 endo),2.71 (2 H, m)(ddd, 4.0, 6.5, 19.3 Hz, em) CDCI, 2.92 (dd, 1.O, 4.1 1.85 (1 H, m), 2.08 (2 H, rn), 2.40 3.20, 3.38 (both d, 13.6 Hz) 1.20, 1.26 Hz) (1 H, m) CDClj 2.28 (d, 3.1 Hz) 1.72 (3 H, m,), 2.00 (1 H, m) 2.95, 3.10 (both d, 13.5 Hz) 0.92, 1.02 3.25,3.40 (both s) CDClj 2.30 (s) 1.80 (3 H, m), 2.00 (1 H, m) 3.00,3.20 (both d, 13.3 Hz) 1.00, 1.10 3.50 (1 H, m), 3.72 (2 H, m), 3.85 1.18, 1.12 (1 H, m) (both t, 7.4 Hz) CDCI, 2.09 (m) 1.87 (3 H, m), 2.09 (1 H, m) 2.99 (em),3.10 (endo)(both d, 0.98 (syn), 1.02 4.05 (2 H, m), 4.13 (1 H, m), 4.30 13.4 Hz) (anti) (1 H,m)CDCI, 2.07 (d, 4.1 Hz) 1.70 (m), 2.07 1.80 (m, endo), 2.96,3.13 (both d, 13.2 Hz) 1.01 (syn), 1.08 3.86 (dd, 5.1, 11.8 Hz, eq), 4.58 1.47 (m, 1.5, (m) 1.91 (m, em) (anti (dt, 9.4, 11.8 Hz, ax), 3.99 (dd, 12.0 Hz, eq), 5.1, 11.8 Hz, eq), 4.46 (dt, 9.4, 2.05 (m, 12.0 11.8 Hz, ax) Hz, ax) 2.18 (d, 4.1 Hz) 1.61 (1 H, m), 1.69(1 H, m), 1.82 3.10, 3.29 (both d, 13.7 Hz) 0.95, 1.12 3.91 (m), 3.99 (m), 4.39 (dt), 4.50 a 4 (1 H,m), 2.07 (3 H, m)' (dt) (both 2.9, 11.8 Hz) 0 (A00 Table 2-continued eAtom(s) erCom-Qapound Solvent 3 4 5 6 8 9, 10 11,12 13 0 2.21 (d, 3.9 ((Hz) 1.75 (m, endo) 1.83 (m), 2.17 2.94, 3.10 (both d, 13.3 Hz) 1.04 (syn),1.08 3.42, 3.49 (both dd, 2.3, 11.3 0.81 (s), 1.18 1.98 (m, exo) (m) (anti Hz), 4.18,4.31 (both d, 11.3 Hz) (s)2.42 (d, 4.0 Hz) 1.93 (2 H, m), 2.00 (1 H, m), 2.09 3.04 (exo), 3.19 (endo) (both d, 1.05, 1.06 3.32, 3.41, 3.48, 3.61 (all 1 H, m)(1 H, m, 5-endo) 13.4 Hz) 2.28 (d, 3.5 Hz) 1.96 (m), 2.28 2.05 (2 H, m) 3.03 (exo), 3.18 (endo) (both d, 1.26 (syn),1.14 2.62 (m, 14.3 Hz), 2.78 (m, 14.4 1.90 (m), 2.19 (m) 13.4 Hz) (anti) Hz), 3.70(ddd, 2.5, 12.9, 14.4 (m)Hz), 3.81 (ddd, 2.6, 12.9, 14.3 Hz)2.29 (d, 3.9 Hz) 1.89 (1 H, m), 2.20 (3 H, m) 3.19, 3.36 (both d, 13.8 Hz) 1.20, 1.25 2.71,2.87 (both m, 14.3 Hz), 1.79 (m), 2.17 3.60, 3.69 (both ddd, 2.7, 12.6, (m)14.3 Hz)3.00 (d, 6.0 Hz) 2.08 (m, endo), 2.05 (2 H, m) 2.99 (exo), 3.22 (endo) (both d, 1.00, 1.08 3.63,3.71, 3.82, 3.90 (all 1 H, m)2.31 (m, exo) 13.7 Hz)2.95 (s) 1.76 (1 H, m), 2.21 (3 H, m) 3.45, 3.78 (both d, 14.0 Hz) 1.00, 1.12 3.81 (2 H, m), 4.54 (1 H, m), 4.77 (1 H, m)3.31 (d, 4.6 Hz) 2.22 (m, endo), 2.06 (m, endo), 3.13 (exo), 3.22 (endo), (both d, 1.09 (syn), 1.21 3.38 (ddd, 2.8,8.5, 16.1 Hz), 2.49 (2 H, m) 2.49 (m, exo) 2.38 (m, exo) 13.4 Hz) (anti 4.29 (ddd, 8.5, 10.2, 16.1 Hz), 3.50 (ddd, 2.8,6.6, 15.0 Hz), 4.03 (ddd, 6.6, 10.2, 15.0 Hz)3.18(d,3.1 Hz) 1.87(1H,m),2.23(1H,m),2.15 3.46, 3.74 (both d, 14.1 Hz) 0.95, 1.13 3.91 (4 H, m) 2.33 (2 H, m)(1 H, m), 2.17 (1 H, m, 5-endo) 3.08 (d, 4.7 Hz) 1.64 (1 H, m), 1.84 (2 H, m), 2.14 3.04, 3.24 (both d, 13.3 Hz) 0.90, 1.08 (1 H,m)3.05 (d, 3.6 Hz) 1.58 (1 H, m), 1.72 (1 H, m), 2.02 3.00, 3.24 (both d, 13.4 Hz) 0.82, 1.00 (2 H,m) Signals of atoms 5-, 6-, and 13-H2 not separated.N m N w Table 3. H NMR spectra (360 MHz) of (camphorsulphony1)oxaziridines;amp;-values (multiplicity, J-values in parentheses). Atom(s) Com-pound Solvent 3 4 5 6 8 9, 10 11,12 13 CDCl, 4.02 (s) 2.28 (d, 4.1 Hz) 1.58 (1 H, m), 1.89 (2 H,), 2.05 3.18,3.41 (both d, 13.5 Hz) 0.98, 1.41 (1 H,m)CDCI, 4.95 (dd, 1.6,4.2 2.32 (t, 4.2 Hz) 1.95 (3 H, m), 2.20 (1 H, m) 3.15, 3.37 (both d, 14.1 Hz) 1.16, 1.23 Hz)CDCI, 2.07 (d, 4.6 Hz) 1.92 (m, 5-exo), 1.86 (m), 1.92 3.09 (endo), 3.32 (exo) (both d, 1.05 (anti),1.35 3.89 (2 H, m), 4.00 (2 H, m)2.17 (m, 5-endo) (m) 13.9 Hz) (syn)CDCI, 2.29 (d, 4.9 Hz) 1.75 (m, 5-1.90 (m, 6-3.05 (endo), 3.27 (exo) (both d, 1.03 (anti),1.29 3.87 (2 H, m), 4.15 (2 H, m) 1.61 (m), 1.79 endo), 1.90 (m, endo), 2.06 (m, 13.9 Hz) (SYn) (m)5-exo) exo) (CD,),CO 2.43 (d, 4.3 Hz) 1.81 (Sendo), 1.77, 1.96,2.09 (all 3.19, 3.65 (both d, 14.4 Hz) 1.10, 1.25 3.84,4.00 (both 1 H, m), 3.96, 1.68 (2 H, m) 1 H, m) 4.06 (both 1 H, m) CDCI, 2.95 (d, 4.3 Hz) 1.68 (1 H, m), 1.98 (1 H, m), 2.10 3.19, 3.38 (both d, 14.1 Hz) 1.05, 1.17 (2 H,m)CDCI, 2.93 (d, 3.9 Hz) 1.62 (1 H, m), 2.00 (3 H, m) 3.15, 3.35 (both d, 14.1 Hz) 1.00, 1.12 CDCI, 2.26 (d, 4.5 Hz) 1.75 (m, 5-endo),1.91 (2 H, m) 3.06 (endo), 3.25 (exo) (both d, 1.04 (anti),1.30 3.89 (2 H, m), 4.17 (2 H, m) 1.60 (1 H, m),1.98 (m, 13.9 Hz) (syn) 1.91 (1 H, m)5-exo) 2.44 (d, 4.3 Hz) 1.79 (m, 5-1.79, 2.04 (both 3.19 (endo), 3.65 (em) (both d, 1.10, 1.26 3.87, 4.04 (both m), 3.97, 4.07 1.68 (2 H, m)endo), 1.94 (m, 1 H, m) 14.4 Hz) (both m) 5-exo) 4 n L W W 0 J.CHEM. SOC. PERKIN TRANS. 1 1990 substitution of the rings with alkyl groups enhances the barrier towards equilibration." This means that, in the case of our spiro compounds, which may be considered as strongly substituted heterocycles, such ring flipping should have quite a high activation energy, and we can expect to observe only the most stable conformations by the NOE measurements, and not an equilibrium mixture.The general absence of NOE effects between the camphor moiety and the heterocyclic rings excludes boat conformations, which would imply very low distances between the central CH, group of the ring and parts of the camphor system, i.e. the bridgehead hydrogen in one and the CHzS02N group in the other boat conformation. The possibility ofchair and some twist conformations remain. In the case of chloroform solutions of the oxaziridines (18b)and (24b), the CHI groups linked to the heteroatoms give rise to only two signals of the axial and equatorial protons (chair conformation assumed), and therefore no detailed analysis of the conformation is possible.An acetone solution of compound (Ub), however, and chloroform solutions of the other spiro compounds, show more strongly split signals of these groups and allow for such an- alysis. The imine (17b)shows the expected couplings (COSY) (over three bonds) of all hydrogens in the dioxane ring, and an additional long-range coupling between two hydrogens of the CH2 groups linked to the oxygens (two dd at 6, 3.86 and 3.99). This is best explained as a W-coupling between equatorial protons and implies that the dioxane ring must have a chair conformation.No NOE effect is observed between these atoms, but quite strong effects are found between all the other hydrogens linked over four bonds where no coupling is observed. This further confirms the chair conformation. The dithiane analogue (20b)shows formally a similar 'H-pattern for the signals of the heterocyclic ring, but, contrary to the dioxane system, a coupling and a strong NOE effect between the signals at 6, 2.62 and 2.78, combined with the absence of both coupling and NOE effects between the hydrogens at 6, 3.70 and 3.81; the signals at 6, 2.62 and 3.81 are caused by one CH, group, and those at 6, 2.78 and 3.70 by the other. This cannot imply a chair conformation, but points to a twisted structure where it is possible to combine a distorted W-arrangement of two hydro- gens with spatial proximity; the larger covalent radius of sulphur, compared with oxygen, assists the distortion from the chair conformation.The oxidation of the sulphur atoms in compound (20b)to form the disulphone-imine (21b) introduces different steric requirements at the sulphur centres, and the conformation of the oxidized dithiane ring switches back to the chair form, as indicated by the absence of coupling but strong NOE effects between the axial hydrogens of the CH, groups linked to oxygen (two ddd at 6, 4.03 and 4.29). However, the ring does not form a perfect chair, as both equatorial hydrogens show W-coupling and an NOE effect (two ddd at 6,, 3.38 and 3.50).As for the dioxane ring, a perfect chair conformation would not allow for NOE effects between these equatorial hydrogens.Surprisingly, the oxidation of the imine (21b) to the oxaziridine (24b)is combined with a rather strong change in the 'euro;3 NMR pattern of the dithiane ring protons. Contrary to the case of the imines, the equatorial hydrogens of the CH2 groups linked to oxygen appear at higher field (6, 4.04and 4.07 us. amp; 3.87 and 3.97 for the axial hydrogens). On the other hand, the chair conformation seems to be maintained, as no coupling but strong NOE effects between the axial hydrogens are observed. If there is some distortion from the perfect chair conformation as in the imine, it cannot be deduced from the data available, as the difference in the chemical shifts of the equatorial hydrogens is too small to determine if an NOE effect is present; however, no W-coupling between these atoms could be detected.Hax As for the conclusions from structural and conformational data with respect to the ability to facilitate enantioselective oxidations, e.g. of sulphides to chiral sulphoxides, it can be expected that the exo-bromo spiro-oxaziridine (7) will not be very different from the simple oxaziridine (l), in that the endo side, where the approach of the substrate to be oxidized occurs, is not much influenced by the em-substituent. The same holds for the dihalogenomethylene oxaziridines (23a)and (23b),since the double bond fixes the substituents in an intermediate plane between the em and endo parts of the molecule.On the other hand, the influence of the endo-bromine in compound (13)can be expected to be considerable, as its large covalent radius will allow the approach of a substrate only in a quite definite position, avoiding steric repulsion between the bromine and the larger parts of the substrate. The influence of the heterocyclic rings in the oxaziridines (18a), (18b), and (24b)should lead to similar effects, although the shielding of one side of the oxaziridine oxygen will probably be a bit less efficient than in the case of bromo compound (13),especially for the almost planar five-membered ring of compound (18a).We will report on such oxidations in due course. ExperimentalNMR spectra were recorded with a Bruker AM 360 instru- ment, with Me,Si as internal standard.Nuclear Overhauser enhancements in the rotating frame were measured with the two-dimensional technique (ROESY) described in the litera- ture l3 (spinlock time 0.3 s). Optical rotations were measured on a Roussel Jouan Digital 71 polarimeter, and IR spectra (KBr) on a Perkin-Elmer 177 spectrophotometer. Mass spectra have been obtained with a Varian CH5 instrument (70eV). Commercially available chemicals were used without further purification. The preparation of (-)-(camphorsulphony1)imine (12) (3aS)-8,8-dimethyl-4,5,6,7-tetrahydro-3H-3a,6-methano-2,l-benzisothiazole 2,2-dioxide and (-)-3-oxo(camphor-sulphony1)imine(16)( 3aS)-8,8-dimethyl-5,6-dihydro-3H-3a,6-methano-2,1-benzisothiazol-7(4H)-one2,2-dio~ide,~*' and* the bromination of compound (12),leading to exo- and endo- J.CHEM. SOC. PERKIN TRANS. 1 1990 3-bromo-(camphorsulphonyl)imines (8) (3aS,7R)-7-bromo-8,s-dimethyl-4,5,6,7-tetrahydro-3H-3a,6-methano-2,1-benziso-thiazole 2,2-dioxideJ and (9) (3aS,7S)-7-bromo-8,8-dimethyl-4,5,6,7-tetrahydro-3H-3a,6-methano-2,l-benzisothiazole 2,2-dioxide, and 3,3-dibromo(camphorsulphonyl)imine (10)(3aS)-7,7-dibromo-8,8-dimethyl-4,5,6,7-tetrahydro-3H-3a,6-methano-2,l -benzisothiazole 2,2-dioxide, as well as the chlorination of compound (12) to form (3aS)-7,7-dichloro- 8,8-dimethyl-3H-3a,6-methano-2,1-benzisothiazole 2,2-dioxide (11) and that of compound (9) to form (3aS,7S)-7-bromo- 7-chloro-8,8-dimethyl-4,5,6,7-tetrahydro-3H-3a,6-methano-2,l -benzisothiazole 2,2-dioxide (14), has already been des- cribedS8 (3aS)-7,7-Dimethoxy-8,8-dimethyl-4,5,6,7-tetrahydro-3H-3a,6-methano-2,l-benzisothiazole2,2-Dioxide (15a) and (3aS)- min.Methanol (200 mi) was added at room temperature, and after storage for 16 h, the precipitate was filtered off, washed successively with lM-sodium hydroxide (100 ml) and water (100 ml), and dried in oacuo for 5 h. It was then dissolved in the minimum amount of chloroform and precipitated with methanol (100-150 ml) to give compound (20a) (90), m.p. 200 "C; a;, + 13.5" (c 1, acetone) (Found: C, 46.9; H, 5.6; N, 4.5. Cl2Hl7N0,S3 requires C, 47.4; H, 5.5; N, 4.5); v,,, 1 660 (C=N), 1 345, and 1 120 cm-' (SO,); m/z 303 (M', 100); and compound (20b) (60), m.p.207 "C; a;' -2.6" (c 1, acetone) (Found: C, 48.8; H, 5.7; N, 4.3. CI3Hl9NO2S3 requires C, 49.2; H, 5.4; N, 4.4); v,,, 1 640 (GN), 1 345, and 1 140 cm-' (SO,); m/z 317 (M', 100). (3aS)-8,8-Dimethyl-5,6-dihydro-3H,4H,7H-3a,6-methano-2,1-benzisothiazole-7-spiro-2'-1',3'-dithiolane 7,7-Diethoxy-8,8-dimethyl-4,5,6,7-tetrahydro-3H-3a,6-methano-2,1-benzisothiazole 2,2-Dioxide (15b).-To a solution of compound (16) (2.0 g, 8.7 mmol) in dichloromethane (50 ml) at -5 "C were added the trialkyl orthoformate (methyl or ethyl, respectively) (60 mmol) and Amberlyst 15 (2.0 g). The mixture was stirred for 12 h at the same temperature, then filtered, and the solvent was evaporated off.The residue was treated with diethyl ether, and the solid product was filtered off, and dried in vacuo (0.1 mmHg; 3 h) to give compound (Ha) (70), m.p. 176deg;C; calk3 +4.0deg; (c 1, acetone) (Found: C, 52.7; H, 7.0;N, 5.1. C12H19N04S requires C, 52.7; H, 7.2; N, 5.1); v, 1650 (C=N), 1335, and 1 165 cm-' (SO,); m/z 274 (M+ + 1, 273, 242 (M+ + 1 -32, lo), and 129 (100); and compound (15b) (4573, m.p. 128 "C; Calk3 -4.0" (c 1, acetone) (Found: C, 55.4; H, 7.7; N, 4.7. C14H23N04S requires C, 55.9; H, 7.6; N, 4.6); v,, 1 660 (GN), 1 350, and 1060 cm-' (SO,); m/z 301 (M+, 573,256 (M' -65,15), and 157 (100). 1 ',1',2,2-3',3 '-Hexa- oxide (21a) and (3aS) 8,8-Dimethyl-5,6-dihydro-3H,4H,7H-3a, 6-methano-2,l-benzisothiazole-7-spiro-2'-1',3'-dithiane 1',1',2,2,3',3'-Hexaoxide (21 b).-To a solution of the spiro compound (20a) or (20b) (10 mmol) in acetic acid (100 ml) was added 30 hydrogen peroxide (60ml, 300 mmol), and the mixture was kept at reflux for 6 h.After cooling to room temperature, the precipitate was filtered off, washed success- ively with water and diethyl ether, and dried in vacuo for 3 h to give compound (21a) (9473, m.p. 293 "C; calk3 -27" (c 1, Me,SO) (Found: C, 39.2; H, 4.7; N, 3.8. C,,H17N06S3 re- quires C, 39.2; H, 4.5; N, 3.8); v,,, 1650 (GN),1 350, and 1 130 cm-' (SO,); m/z 303 (M+ -64,3573, 288 (M+ -79, 25), and 132 (100); and compound (21b) (90), m.p. 293 "C; a;' +8.0" (c 1, Me,SO) (Found: C, 40.9; H, 4.9; N, 3.8. C13H19N06S3 requires C, 41.0; H, 4.9; N, 3.7); vmsx 1640 (C=N), 1330, 1345, and 1130 cm-' (SO,); m/z 381 (M+, lo), 317 (M+ -64,21), and 108 (100).(3aS)-8,8-Dimethyl-5,6-dihydro-3H,4H,7H-3a,6-methano-2,1-(3aS)-7-Dichloromethylene-8,8-dimethyl-4,5,6,7-tetrahydro-benzisothiazole-7-spiro-2'-1 ',3'-dioxolane 2,2-Dioxide (17a), (3aS)-8,8-Dimethyl-5,6-dihydro-3H,4H,7H-3a,6-methano-2,1-benzisothiazole-7-spiro-2'-1',3'-dioxane 2,2-Dioxide (17b), and (3aS)-5',5',8,8-Tetramethyl-5,6-dihydro-3H,4H,7H-3a,6-methano-2,1-benzisothiazole-l-spiro-1 ',3'-dioxane 2,2- Dioxide (19).-To a solution of compound (16) (2.0 g, 8.7 mmol) in toluene (100 ml) were added the corresponding glycol (43 mmol) and toluene-4-sulphonic acid (PTSA) (1.0 g). The mixture was heated to reflux with azeotropic removal of water for 7 days, and was then extracted successively with h-sodium hydroxide (100 ml) and water (100 ml), and dried with sodium sulphate. On concentration of the solution to 30 ml, the products crystallized out to afford compound (17a) (51), m.p.218 "C; Calk2 + 11.5' (c 1, acetone) (Found C, 52.6; H, 6.1; N, 5.0. ClZH17N04S requires C, 53.1; H, 6.1; N, 5.2); v,,, 1 665 (C=N) and 1340 cm-' (SO,); m/z 271 (M+, 16) and 127 (100); compound (17b) (52), m.p. 205 "C; a;, +21.5" (c 1, acetone) (Found C, 54.4; H, 6.1; N, 4.8. C13H19N04S requires C, 54.7; H, 6.7; N, 4.9); v,,, 1 655 (GN) 1350 cm-' (SO,); m/z 285 (M', 20) and 141 (100); and compound (19) (46), m.p. 174 "C; a$, + 18.0" (c 1, CHCl,) (Found C, 57.0; H, 7.4; N, 4.4. Cl,H,,N04S requires C, 57.5; H, 7.3; N, 4.5); v,,, 1 640(C=N), 1 335, and 1 170 cm-' (SO,); m/z 313 (M', 16), 249 (M+ -64,32), and 169 (100).(3aS)-8,8-Dimethyl-5,6-dihydro-3H,4H77H-3a,6-methano-2,1-benzisothiazole-7-spiro-2'-1',3'-dithiolane 2,2-Dioxide (20a) and (3aS)-8,8-DimethyI-5,6-dihydro-3H,4H,7H-3a,6-methano-2,1-benzisothiazole-7-spiro-2'-1 ',3'-dithiane 2,2- Dioxide (2Ob).-To a solution of the dithiol (32 mmol) in toluene (100 ml) was added a solution of (16) (7.2 g, 32 mmol) under nitrogen. A solution of BF,-diethyl ether complex (4.5 g) in toluene (50ml) was added dropwise, and the mixture was heated to reflux for 90 3 H- 3a,6-me thano- 2,l- benziso th iazole 2,2- D ioxide (22a) and (3aS)-7-Dibromomethylene-8,8-dimethyl-4,5,6,7-tetrahydro-3H-3a,6-methano-2,1-benzisothiazole2,2-Dioxide (22b).-To a sol- ution of imine (16) (4.4 g, 20 mmmol) and triphenylphosphine (10.5 g, 40 mmol) in dichloromethane (100 ml) was added dropwise a solution of CBr, (10.0 g, 30 mmol) or CCl, (4.6 g, 30 mmol) in dichloromethane (50 ml).The mixture was stirred for 16 h, concentrated to ca.80 ml, and the product was puri- fied by column chromatography (silica gel; dichloromethane- diethyl ether, 3:2). The products were eluted as the second band. Compound (22a) (45), m.p. 186 "C; Calk3 +82.5" (c 1, acetone) (Found: C, 45.0; H, 4.5; N, 4.8. C1,H13C12N02S requires C, 45.0; H, 4.4; N, 4.8); v,,, 1 630 (C=N), 1605 (M),1330 and 1 120 cm-' (SO,); m/z (rel. 37Cl) 297 (M+, 4), 233 (M+ -64,lo), and 196 (M+ -101,100).Compound (22b) (44), m.p. 178deg;C; aJk3 +94O (c 1, acetone) (Found: C, 34.2; H, 3.3; N, 3.6. CllH13BrZN02S requires C, 34.6; H, 3.4; N, 3.7); vmax 1610 (GN),1590 (M),1330 cm-' (SO,); m/z (rel. 81Br) 385 (M+,573, 317 (M+ -64, 16), and 69 (100). (4aS,8R,8aR)-8-Bromo-9,9-dimethyl-5,6,7,8-tetrahydro-4H-4a,7-methano-oxazirino 3,2-i 2,1 benzisothiazole 3,3-Dioxiamp; (7)and (4aS,8S,8aR)-8-Bromo-9,9-dimethyI-5,6,7,8-tetrahydro-4H-4a,7-methano-oxazirino3,2-i2,1benzisothiazole3,3-Di-oxide (13).-Compound (7). To an efficiently stirred, 2-phase mixture (3: 7) of the bromoimines (8)and (9) (2.9 g, 10 mmol) in dichloromethane (100 ml) and sodium carbonate (1.5 g, 15 mmol) in water (50ml) was added dropwise a solution of 50 MCPBA (4.6 g, 15 mmol) in dichloromethane (100 ml).The mixture was stirred for 2 days, after which time the organic phase was extracted with brine (3 x 150 ml) and dried over sodium sulphate. After concentration to 20 ml and addition of diethyl J. CHEM. SOC. PERKIN TRANS. 1 1990 ether (100 ml), a mixture of imine (9)and the oxaziridine (7) (7:3) precipitated out (2.5 g), and could be used directly for oxidations. Compound (13). To an efficiently stirred, 2-phase mixture (3:7) of the bromoimines (8) and (9) (2.9 g, 10 mmol) in dichloromethane (50 ml) and sodium carbonate (4.9 g, 50 mmol) in water (50 ml) was added dropwise a solution of 50 MCPBA (15.5 g, 50 mmol) in dichloromethane (80 ml).The mixture was stirred for 5 days, and the organic phase was then extracted successively with saturated aq. sodium hydrogen carbonate (3 x 150 ml) and brine (6 x 150 ml), rapidly with 10 aq. sodium sulphite (3 x 100 ml), and finally with brine (2 x 100 ml). After being dried over sodium sulphate, the mixture was concentrated to 20 ml and the product was precipitated by the addition of diethyl ether (80 ml) to afford compound (13) (0.88 g, 30), m.p. 154 "C; a;, +130" (c 1 acetone) (Found: C, 38.8; H, 4.7; N, 4.5. CloHI4BrNO3S requires C, 39.0; H, 4.5; N, 4.5); vmax1370 and 1 170 cm-' (SO,); mjz (rel. "Br) 309 (M', 9), 228 (M' -81,16), and 148 (100). 2927 (4aS,8aR)-9,9-Dimethyl-6,7-dihydro-4H,SH,8H-4a,7-meth-ano-oxazirino 3,2-i 2,1 benzisothiazole-8-spiro-2'-1 ',3'-dithiol- ane 1',1',3,3,3',3'-Hexaoxide(24a) and (4aS,8aR)-9,9-Dimethyl- 6,7-dihydro-4H,5H,8H-4a,7-methano-oxazirino3,241 2,1 -benzisothiazole-8-spiro-2'-1',3'-dithiane 1 ',1',3,3,3',3'- Hexaoxide (24b).-To an efficiently stirred, 2-phase mixture of an imine (20a) or (20b) (10 mmol) in dichloromethane (20 ml) and sodium carbonate (56.0 g, 300 mmol) in water (200 ml) was added a solution of 50 MCPBA (93.0 g, 300 mmol) in dichloromethane (200 ml) dropwise. The mixture was stirred for 7 days, after which time the organic phase was extracted successively with brine (6 x 200 ml) and water (4 x 100 ml), and dried over sodium sulphate.After concentration to 30 ml, the products were precipitated with diethyl ether (100 ml) at -10 "C.Compound (24a) could not be obtained pure. Com- pound (24b) (lo), m.p. 245 "C; aJzDj +60deg; (c 0.3, acetone) (Found: C, 39.4; H, 5.0; N, 3.5. CI3Hl9NO7S3 requires C, 39.3; (4aS,8aR)-9,9-Dimethyl-6,7-dihydro-4H,5H,8H-4a,7-meth-ano-oxazirino 3,241 2,1 benzisothiazole-8-spiro-2'-1',3'-dioxol-ane 3,3-Dioxide (18a) and (4aS,8aR)-9,9-Dimethyl-6,7-dihydro-4H,5H,8H-4a,7-methano-oxazirino3,2-i2,1benzisothiazole-8-spiro-2'-1',3'-dioxane 3,3-Dioxide (18b).-To a stirred, 2- phase mixture of an imine (17a) or (17b) (20 mmol) in dichloromethane (50 ml) and sodium carbonate C(5.7 g, 30 mmol) for (17a), (11.4 g, 60mmol) for (17b)l in water (100 ml) was added dropwise a solution of 50 MCPBA C(9.3 g, 30 mmol) for (17a), (18.6 g, 60 mmol) for (17b)l in dichloro- methane (100 ml).The mixture was stirred for 2 days after which time the organic layer was separated and washed with brine (3 x 100 ml). After being dried over sodium sulphate, the solution was concentrated to 30 ml, and the product was precipitated with diethyl ether (80 ml). Compound (Ma) (7573, m.p. 18OOC (decomp.); a);, +75.5" (c 1, acetone) (Found: C, 50.2; H, 6.1; N, 4.8. C12H,,N05S requires C, 50.1; H, 5.9; N, 4.9); v,,, 1 370 and 1 175 cm-' (SO,); m/z 287 (M', 35) and 181 (100). Compound (18b) @OX), m.p. 186 "C (decomp.); a;, +65.0deg; (c 1, acetone) (Found: C, 43.6; H, 6.2; N, 4.8. CI3HI9NOSS requires C, 43.8; H, 6.3; N, 4.6); v,,, 1375 and 1170 cm-' (SO,); mlz 301 (M', 28) and 139 (W.(4aS,8aR)-8-Dichloromethylene-9,9-dimethyl-5,6,7,8-tetra-hydro-4H-4a,7-methano-oxazirino3,2-i2,1 benzisothiazole 3,3-Dioxide (23a) and (4aS,8aR)-8-Dibromomethylene-9,9-dimethyl-5,6,7,8-tetrahydro-4H-4a,7-methano-oxazirino3,241-2,lbenzisothiazole 3,3-Dioxide (23b).-To an efficiently stirred, 2-phase mixture of an imine (22a) or (22b) (3.0 mmol) in dichloromethane (50 ml) and sodium carbonate (2.9 g, 30 mmol) in water (100 ml) was added dropwise a solution of 50 MCPBA (9.3 g, 30 mmol) in dichloromethane (100 ml). The mixture was stirred for 7 days, after which time the organic phase was extracted with brine (3 x 200 ml) and dried with sodium sulphate. The solution was then concentrated to 30 ml, and the products were precipitated with diethyl ether (100 ml) and purified by recrystallization from chloroform-diethyl ether (1 :2).Compound (234(28), m.p. 134 "C; calk3 + 103" (c 1, acetone) (Found C, 42.6; H, 4.0;N, 4.2. C11H13C12N03S requires C, 42.7; H, 4.2; N, 4.5); v,,, 1 605 (C=C), 1 360, and 1 230 cm-' (SO,); m/z (rel. 37CI) 313 (M+,473, 249 (M' -64, 13), and 158 (100). Compound (23b) (32), m.p. 153 "C; a:: + 112" (c 0.5, acetone) (Found: C, 32.9; H, 3.3; N, 3.7. Cl1Hl,Br,NO3S requires C, 33.2; H, 3.3; N, 3.5); v,,, 1 590 (W)and 1 360 cm-' (SO,); mlz (rel. "Br) 401 (M', 373, 321 (M' -80, 6), and 67 (1 00). H, 4.8;N, 3.5); vmax1 370, 1 170, and 1 150 cm-' (SO,); m/z 301 (M' -96,579 and 108 (100). AcknowledgementsWe thank Prof.Dr. Ivar Ugi, TU Miinchen, for supporting this work. 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