606 J.C.S. Perkin IReactions of Unsaturated 1.3-Dioxan Derivatives. Part V1.t Addition of2-(2-Furyl)-1,3-dioxan and its Derivatives to Maleic AnhydrideBy Jolanta Mablifiska-Solich, Institute of Polymer Chemistry and Technology, Silesian Technical University,The reaction of 2-(2-furyI)-1,3-dioxan with maleic anhydride in diethyl ether or benzene i s stereochemicallyheterogeneous, yielding a mixture of endo- and exo-adducts. The structures of these adducts have been studiedby means of bromination and lactonization reactions and i.r. and n.m.r. spectroscopy.44-1 00 Gliwice, PolandIT is generally accepted that diene addition reactions arestereochemically non-homogeneous. The steric outcomedepends upon the reaction conditions, the endo-adductbeing. formed more rapidly, but being less thermo-dynamically stable than the exo-isomer, which is the pre-dominant product of reaction for prolonged periods or athigh temperatures.lThe stereochemistry of the reaction of furan withmaleic anhydride or maleic acid has been considered interms of an endo-exo-adduct equilibrium.2 It seemedprobable that the introduction of a 1,3-dioxan-2-ylsubstituent into the furan ring would change the equilib-t Part V, ref.4l K. Alder, F. W. Chambers, and W. Trimborn, Annalen, 1960,666, 27.rium situation. Mavoungou-Gomes has reported abrief study of the reactions of 2-(2-furyl)-1,3-dioxolanand 2-(2-furyl)-1,3-dioxan with maleic anhydride in di-ethyl ether at 0 "C, and proposed, on the basis of n.m.r.analysis, that the products had the exo-configuration.The present paper shows that this assumption was in-correct.We have recently reported that 2-(2-furyl)-5,5-dimethyl-l,3-dioxan and maleic anhydride give twostereoisomeric adducts (1 : 1) when the reaction iscarried out at 0-20 "C.In an attempt to investigate the generality of stereo-J. A. Berson and R. Swidler, J. Amer. Chem. Soc., 1963, 75,L. Mavoungou-Gomes, Bull. SOC. chim. France, 1967, 1763.4 J.. MaSlidska-Solich and 2. Jedlifiski, Bull. Acad. poEon. Sci.,1721.Sev Scz. chim., 1974, 22, 7491975chemically non-homogeneous 2-(2-furyl)-1,3-dioxan addi-tions to maleic anhydride, some 2-(2-furyl)-1,3-dioxanwith various alkyl substituents in the acetal ring havebeen studied.RESULTS AND DISCUSSIONDiels-Alder Addition.-The reaction of 2-(2-furyl)-1,3-dioxans with maleic anhydride was carried out intemperature ranges 0-20 and 60-80 "C in diethylether, benzene, or toluene.The products were all 1 : 1adducts [(l) and (Z)], except in the case of 2-(2-furyl)-4-methyl-l,3-dioxan and maleic anhydride, which formed a1 : 2 adduct at 70 "C. All 2-(2-furyl)-1,3-dioxans reactwith maleic anhydride to form in the first stage 1 : 1charge-transfer complexes,6 as verified by n.m.r. spec-troscopy. The complex of 2-(2-furyl)-4methyl-1,3-dioxan and maleic anhydride undergoes an ' intra-com-plex ' reaction, yielding a cyclic adduct, with simul-taneous complexation of a second molecule of maleicanhydride.6H-4 (s)4.824.84-824.64.84.7G4-724-754.65.534.654.754.854.84.76H-5,H-6 (t)3-63.63.553.43.63.583.53.623.53.33.383-53.473.573.45Reaction at 0-20 "C607ducts were elucidated on the basis of i.r.and n.m.r. dataand chemical transformations.'0( 1 1 e x o ( 2 ) endoa; X = [CH,], f ; X = CH,-CMe,.CH,b; X = CHMe*[CH& g; X = CH,*CMe,CHPr'c ; X = CHMeCH,CHMe h; X = CH,CMeEt-CH,e; X = [CHMe],d ; X = CHMeCH,CMe, I ; X = CH,*CEt,.CH*The i.r. spectra of all adducts showed characteristicanhydride carbonyl absorptions at 1880-1860 and1780-1795 cm-1, with no apparent difference betweenendo- and exo-isomers. In the i.r. spectrum of theadduct (1 g ) , however, the anhydride carbonyl absorptionTABLE 1Chemical shifts ( T) of Diels-Alder addition products1,3-Dioxan-2-yi substituent1.. I . .IH(2 (d) H-3 (d)6-6 8-826.056-62 6.825.956.35 6.756.0766.6 6.88-876.45 6.628.5 6.755.06.6 6.766-05OCH-o (s) OI\Ie CH.05.125.053.14.87j.15.04.94.585.14 - i i5.05.17 {E5-225-075.9-6.48.5.7-6.55.9-6'1,.5*6-6*25.9-6.46.4-6.45.9-6.055.9-6.25.7-6.16.06-6.56.05-6'56.0-6.56.1-6.5in most cases gave two com-pounds (la-i) and (2a-f, h, and i), whereas reaction at60-80 "C gave only one isomer (1). An exception wasthe reaction of 2- (2-furyl) -6-isopropyl-5 ,fi-dimet hyl-1,3-dioxan, which also gave one isomer only at 0-20 "C.The products obtained at 0-20 "C decompose in airwith irreversible destruction of 2-furyl-l,3-dioxans tofurfuraldehyde. This is shown by darkening of theproducts and by the appearance of carbonyl i.r.absorp-tion (1665 cm-l). The pure adducts (la-i) on the otherhand are much more stable, and on hydrolysis of theanhydride ring, yield diacids or carboxy-esters.Structures of t h Adducts.-The structures of the pro-& J. MaSlifiska-Solich, Roczniki Chem., 1976, 49, No. 3.Me-ax8.68.68.848.88.75Me-q8.528.529.1694359.3CH McCH . k'l"8.5-8.728.5-8.728.1 -8.68.1--8.58.1-8.58.1-8.58.4-8'08.4-8.98.3-9.08.3-9.08.12 (d)8.2-9.08.2-9.08.28.26.66-967.066-187-16.767-567.26appears as three peaks at 1865, 1845, and 1785 cm-1,corresponding to two symmetric and one asymmetricstretching vibrations, respectively.In the n.m.r.spectra of the adducts (la-i) the H-2 and-3 signals form a simple AB quartet at T ca. 6.75 and cu.6-5 ( J 64-7-65 Hz). The magnitude of the couplingconstants suggested that H-2 and -3 have the endo-configuration. The exo-configuration of H-2 and -3 inthe endo-adducts (2) would be expected to result in an ABquartet with J 10-12 Hz. Chemical shifts and couplingconstants are summarized in Table 1.The n.m.r. spectra of the adducts obtained at 0-20 "C[mixtures of (1) and (2) J exhibited the same signals as theexo-isomers ( l ) , along with further signals correspondin608 J.C.S. Perkin Ito H-2 and -3 (as doublets) and the 0-CH.0 (acetal)proton, deshielded by ca. 0.65 and 0.1 p.p.m., respec-tively.This deshielding effect is probably obscured bythe anisotropic effects of lone-pair electrons on carbonyloxygen atoms in the endo-isomers. The differences inchemical shift of these protons facilitate quantitativeanalysis of endo-composition in the mixtures of adducts.Additional distinctive features in the n.m.r. spectra arethe shifts of 4- and 6-methyl protons in the 1,3-dioxanunit. Methyl signals were observed as two separatedoublets (lb, c, and g), as four doublets (2c), and as threedoublets (2b), J 6.3 Hz, showing temperature-dependentarea ratios. These methyl signals at 45 "C coalesce toone doublet in the cases of 2-(2-furyl)-4-methyl-, 2-(2-f uryl)-4,6-dimethyl-, and 2- (2-f uryl) -6-isopropyl-5,5-di-methyl-l,3-dioxans. This effect disappeared after cleav-age of the anhydride ring in the adducts (Table 1).Thusthe rotational isomerism of the 4-methyl-, 4,6-dimethyl-,or 6-isopropyl-5,5-dimethyl-l,3-dioxan-2-yl substituent(presumably in a chair or a distorted chair form) isapparently due to steric hindrance by the 5-memberedand the appearance of new peaks at T 2.55, 3.6, and 4-65(due to H-5, -4, and -3 of the fury1 substituent) and asinglet at T 2.8 (two protons of maleic anhydride). Thechemical shifts of the protons of the adducts (1) and (2)and their coupling constants were markedly solvent-dependent. In [2H]chlor~form or C2H,]pyridine, H-2and -3 of the adducts gave rise to singlets in the range7 6-75-7.0, instead of two doublets. This effect is notobserved in the case of the furan-maleic anhydrideadduct, and is believed to be due to a second-order n.m.r.phenomenon, i.e.the difference in chemical shiftsbetween H-2 and -3 being of the same order as thecoupling constant.N.m.r. studies of the adducts obtained at 0-20 "Cshowed no clear correlation between the coupling con-stants of H-2 and -3 in the endo-adducts (Table 1) ; thusthese were of no help in determination of their configur-ation.The structures of the adducts were confirmed by astudy of their chemical reactions. Attempts to separatethe mixtures of endo- and exo-isomers were unsuccessful.( 3 1SCHEME 1 t For convenience, these compound numbers are also used to refer to the corresponding methyl (or ethyl) esters [cj. (7)and (811anhydride ring.At elevated temperature the rotationprocess changes the environment of the 1,3-dioxan-2-y1substituent and thus renders the methyl groups mag-netically equivalent.Steric hindrance of alkyl substituents at C-4 and -6in the 1,3-dioxan ring in both endo- and exo-isomers in-fluenced the rate of Diels-Alder addition, and theendo : exo ratio. The presence of large groups at C-4 and-6 disfavours formation of the endo-adduct. In fact, noendo-isomer of compound (9) was detected. The orderof activity of 2-furyl-1,3-dioxans is as follows: a f -i h b c d g e. The variation of productcomposition with time (Table 2) unambiguously estab-lishes that the 2- (2-f uryl) -5,5-diethyl- 1,3-dioxan-maleicanhydride reaction follows the typical kinetic-energeticpattern.endo-Addition is a rate-favoured process butthe endo-adduct is thermodynamically unstable withrespect to the exo-adduct, which gradually accumulates atthe expense of the former.A repulsive steric interaction between the 1,3-dioxanring and the endo-anhydride ring is probably a cause ofthe low stability of the endo-adducts. In polar solventssuch as acetone, chloroform, and pyridine the endo-adducts (2a-i) decompose even at ambient temperature(in 2-10 h), regenerating the maleic anhydride and 2-(2-furyl)-l,3-dioxans. This is confirmed by the disappear-ance of the n.m.r. doublets due to H-2 and -3 (7 ca. 6.0)Therefore attempts were made to isolate them as stablederivatives. Since saturation of the olefinic bond of theadducts renders them incapable of reversion to theircomponents, the first attempts involved the directbromination of the reaction mixture obtained at 0-20 "C.The initial crystalline product which precipitated uponbromination in carbon tetrachloride or chloroform con-sisted of the crude dibromo-anhydride (4), which wasidentical with the compound obtained upon brominationof the adduct (1).The mother liquors contained thebromo-lactone acids (5) and (6) (Scheme 1). The struc-tures of these compounds were determined by i.r. andn.m.r. spectroscopy.TABLE 2Composition of products of the 5,5-diethyl-2- (2-fury1)-1,3-dioxan-maleic anhydride reaction tTime (days) exo-Isomer endo-Isomer Total1 14 86 21.62 18 72 38.74 35 66 66-26 46.9 64.1 96.4(%) (%) Yield (%)t All runs a t 0 "C; reagents: 5,6-diethyl-2-(2-furyl)-1,3-dioxan (0.1 mol) and maleic anhydride (0.1 mol) in diethylether (100 ml) ; compositions estimated by n.m.r.spectroscopy.The i.r. spectra of the dibromo-anhydrides (4) showedtwo peaks at 1790 and 1880 cm-l, corresponding to th1975 609anhydride carbonyl groups. The lH n.m.r. parameters,in particular the coupling constants (Js,6 3.1 Hz), showedconclusively that the vicinal protons H-5 and -6 of thedibromo-adducts were in the trans-position. Since 1-( 1,3-dioxan-2-yl)-7-oxabicyclo[2.2.1] hept-5-ene-2,3-di-carboxylic anhydrides [(I) and (2)] have no symmetry atC-1 and -4, two isomers of the trans-dibromo-adducts[(3) and (4)J should be expected to be formed.Thesepairs of dibromo-adducts may be distinguished by theirJ,,s values. In the n.m.r. spectra of the dibromo-adducts the H-4 signal appears as a singlet, from which it(1) and (2) by brominating their methyl(ethy1) esterpotassium salts. This latter reaction gave a mixture offour bromo-lactone esters (5)-(8), of which two [(5) and(6)J were identical with the products derived from directbromination. Compounds (7) and (8) were identicalwith the bromo-lactone esters obtained by brominationof the methyl(ethy1) ester potassium salts of the adduct(1) (Scheme 2).The formation of compounds (7) and (8) can be ex-plained on the basis of a Wagner-Meerwein rearrange-ment similar to that involved in the lactone formationCH +0-TABLE 3Chemical shifts (T) and coupling constants (Hz) for the isomeric bromo-lactones (5f), (6f), (7f), and (8f)rA - _- -Compound H o H E H A HB477 (d) 4.87 (s) 6.29 (d) 6.76 (4)4.9br (s) 6.16 6.87 (d) 6.4 (4)6.4 (m) 6.52 6-55 (d) 6.96 (9)6.2 (m) 6-45 6-62 (d) 6.92 (4)(6f) a(Of)(7f)(8f)a Methyl ester.follows that the ring protons at C-5 and -4 are endo,exo-disposed and the compounds have structure (4).The i.r.spectra of the bromo-lactone acids (5) and (6)showed characteristic absorptions for the Iactone groupat 1795-1820 cm-l and for the acid group at 1715-1725cm-1. The formation of the bromo-lactone acids fromthe adducts obtained at 0-20 "C may be explained interms of the mechanism described by Woodward andBaer.' This reaction can proceed only in the presence ofsome water and if the adduct (2) has the endo-configur-ation.Esterification of the bromo-lactone acids (5) and (6)with diazomethane yielded a mixture of two bromo-lactone esters, which were separated by fractional crystal-lization.These products were compared with the bromo-lactone esters obtained from a mixture of the adductsD. Gagnaire and E.1963, 2627.Payo-Subiza, Bull. SOC. chim. France,HD JCD JBD JBC JCE JAB4.3 (t) 4.5 4.6 0 0 11-65-01 (d) 0 4.6 0 0 11-63.86 (d) 3.0 0 4.5 1.6 10.865.36 0 4.5 0 1.6 10.2Ethyl ester.from exo- 7-oxabic yclo [ 2.2.13 hep t-fi-ene-2,3-dicarboxylicanhydride.'The stereochemistry of the bromo-lactone esters (5)-(8) was unambiguously confirmed by their n.m.r.spectra.Data for the products derived from the 2-(2-furyl)-5,5-dimethyl-l,3-dioxan-maleic anhydride adduct are givenin Table 3. The coupling constants of HA and HB(J 10-2-11.5 Hz) prove their exo-positions in all fourcases. Compounds (5) and (6) were distinguished from(7) and (8) by the Hc signal, which in (5) and (6) occurs a tlower field (by ca. 80 Hz), owing to deshielding by theoxygen atom. Moreover, the doublet corresponding toHD in (7) is at low field (T 3-8-3.9) owing to the com-bined effects of the two adjacent oxygen atoms. Asmight be expected on simple electronegativity groundsthe acetal proton in (8) produces a signal at lower field7 R. B. Woodward and H. Baer, J. Amer. Chem. SOC., 1948,70,1161610 J.C.S.Perkin I( s 46-47) than those in compounds (5)-(7). Furtherconfirmation is provided by the coupling constants of aUthe bromo-lactone esters (Table 3). Gagnaire and Payo-Subiza,G who examined a series of 7-oxabicyclo[2.2.1]-hept-2-ene derivatives, gave the following average valuesof the coupling constants for vicinal protons in these sys-tems: bridge,endo, 0; bridge,exo, 4.2-5.0; exo,exo,11-11.4; endo,endo, 7, and endo,exo, 0-3.2 Hz. Then.m.r. spectra of compounds (5)-(8) are consistent withthese average values.The present findings indicate that the ratio of yields ofthe isomeric bromo-lactones (5)-(8) depends on twofactors: the steric effect of the alkyl-substituted 1,3-dioxan ring, governing the direction of initial attack ofbromine on the double bond; and the position of attackby bromine (at C-5 or -6).Compounds (5), (7), and (8)are formed by initial attack of the bromine on the acidsalt from the exo-side, at C-6 in the case of (5) and (7) andat C-5 in the case of (8). The esters (5) were obtainedfrom the endo-adducts (2) as the main product of thereaction with the bromine. The isomers (6) were onlyobtained from the endo-adducts (2a and f). The pre-dominance of the bromo-lactone esters (8) obtained fromexo-adduct is consistent with the previous observationsof greater steric hindrance by alkyl groups at C-4 and -6of the 1,3-dioxan ring than by those at C-5. Such stereo-chemical influence by the 1,3-dioxan-2-y1 substituentcontrols the preference for the formation of the isomericbromo-lactone esters (5), (7), or (8).EXPERIMENTAL1H N.m.r.spectra were determined with Varian XL-1001.r. spectra were determinedThe 2-(2-furyl)-and JEOL-60 H instruments.with a Unicam SP 200 spectrophotometer.1,3-dioxans were prepared according to the publishedprocedure.Prepayation of the Adducts ( 1) and (2) .--General procedure.All the adducts were prepared in the same manner. Sub-limed maleic anhydride (0.1 mol) was dissolved in diethylether, benzene, or toluene (100 ml) and an equivalent quan-tity of the 2-(2-furyl)- 1,3-dioxan derivative was added.The solution was kept at 0 "C or at room temperature forseveral days, or at 60-80 "C for between 15 min and 9 11.The crystals were filtered off and recrystallized.1-( 1,3-Dioxan-2-yl) -7-oxabicyclo[ 2.2.1 J hept-5-ene-2,Sdi-carboxylic anhydride.The exo-isomer (la) was obtained at76 "C (15 min) as white crystals (92%), m.p. 125-126"(from ethanol). The mixture of endo- (2a) (56%) and exo-isomers was obtained at 0 "C in diethyl ether ( 5 days) ; m.p.86-86"; yield 83% (Found: C, 57.0; H, 4.9. Calc. forC,,H,,O,: C, 57.1; H, 4.8%).1-(4-Methyl- 1,3-dioxan-2-yC)-7-oxabicycZo[ 2.2. IIhept-5-ene-2,3-dicarboxyZic anhydride. The exo-isomer complexed withmaleic anhydride was obtained at 70 "C (5 h); yield 89y0.Crystallization from propan-2-01 gave the pure exo-isomer(lb), m.p. 106-107' (Found: C, 58.5; H, 5-1. C13H1406requires C , 58.6; H, 5.2%). The mixture of endo- (45%)(2b) and exo-isomers was obtained at 0 "C (6 days) as whitecrystals, which were washed with diethyl ether; m.p.78-94" (Found: C, 57.8; H, 4.8%).1-(4,6-Dimethyl- 1,3-dioxan-2-yl)-7-oxabicycl0[2.2.l]hept-5-ene-2,3-dicarboxylic anhydride. The exo-isomer (lc) wasobtained at 75 "C in toluene (6 h); yield 88%; m.p. 109-109.6O (from propan-2-01). The mixture of endo-(36%) (2c)and exo-isomers was obtained at 0" (8 days) and was washedwith cold methanol; m.p. 87-89"; yield 68% [Found: C,58.4; H, 6.1 (for mixture); C, 60.2; H, 5.9 (for exo-isomer).C1,H,,O, requires C, 60.0; H, 5-75y0].1-( 4,4,6-Trimethyl- 1,3-dioxan-2-yl)-7-oxabicyclo[ 2.2.1 Jhept-5-ene-2,3-dicarboxylic anhydride. The exo-isomer (Id) wasobtained at 70 "C in benzene (7 h); m.p. 104-106°. Themixture of endo- (2d) (26%) and exo-isomers was obtainedat 0-20' (21 days); m.p.90-93" [Found: C, 61.0; H, 8.0(for exo-isomer); C, 69.2; H, 5.8 (for mixture). C,,H,,O,requires C, 61-2; H, 6.15y0].The methyl half-ester corresponding to (Id) had m.p.118-120" (Found: C, 58.9; H, 6.9. Calc. for C1,H,,O,:C, 58-9; H, 6.75y0), vmX 1715 ( G O acid) and 1745 ( G Oester) cm-1, T [(CD,),CO] 3.68 (2H, q, J 6.0 Hz, H-5 and -6),4.72br (lH, s, J 1.5 Hz, H-4), 4.8 (lH, s, acetal H), 7.05 (lH,d, H-3), 7.22 (lH, d, J 9-15, H-2), 6.45 (3H, s OCH,), 4.26(lH, m, CH*O), 8.45-8-97 ( l l H , m, CH, and CH,), and0.5br (lH, s, C0,H).1-(4,5,6-Trimethyl- 1,3-dioxan-2-yl)-7-oxabZcycZo[2.2.1] hept-5-ene-2,3-dicarboxylic anhydride. The exo-isomer ( le) wasobtained at 70 "C (9 h) in benzene; yield 86% ; m.p.102-104". The mixture of endo- (2e) (24%) and exo-isomers wasobtained at 0" (34 days) ; yield 68% ; m.p. 82-92' [Found:C, 61.1; H, 6.0 (for exo-isomer); C, 58.2; H, 5-6 (for mix-ture).1-( 5,5-DiethyZ- 1,3-dioxan-2-yZ)-7-oxabicyclo[ 2.2.llhept-5-ene-2,3-dicarboxyZic anhydride. The exo-isomer (li) wasobtained at 70 "C (90 min); yield 95%; m.p. 109-111".The mixture (46% endo) was obtained in toluene (6 days) at0 "C; yield 89%; m.p. 87-89" (Found: C, 62.5; H, 6.4.Calc. for Cl6H,,O,: C, 62.3; H, 6.55%).1 - (6-Isopropyl-5, 5-dimethyl- 1 , 3-dioxan-2-yl) -7-oxabicycEo-[2.2.l]hept-5-ene-2,3-dicarboxylic anhydride. The exo-iso-mey (lg) was obtained at 0 "C (24 days; 75% yield) and at70 "C (7 h ; 84%); m.p. 103-104" (Found: C , 63.5; H, 7.1.C,,H,,O, requires C, 63.35; H, 6.9%).1-(5-Ethyl-5-unethyl- 1,3-dioxan-2-yl)-7-oxabicycZ0[2.2.1]-hept-5-ene-2,3-dicarboxylic anhydride. The exo-isomer (lh)was obtained at 75 "C (2 h); yield 95%; m.p.10'8-110".The mixture (50% endo) was obtained after 5 days at 0 "C;yield 92%; m.p. 92-93' (Found: C, 61.2; H, 6.2. Calc.for C,,H,,O,: C, 61.2; H, 6.1%). The adducts (lh) and(2h) are isomeric mixtures (isomers not isolated) withdifferent stereochemistry a t C-5 of the 1,3-dioxan ring.Brominatiort ofAdducts.-To a solution of the adduct (0.1mol) in chloroform or carbon tetrachloride (150 ml) wasadded bromine (5.5 ml) in one portion. The mixture waskept at room temperature for 24 h. Much hydrogen bro-mide was evolved in the case of adducts obtained at 0-20"C.The precipitate (4a, b, f , h, or i) was separated and wasidentical with the product of direct bromination of theadducts (1). The dibromo-anhydrides (4c, d, g, and e) arerather unstable and are hydrolysed readily at room tempera-ture, especially when exposed to air. By crystallization fromalcohols these products were converted into half-esters ordiesters (vmx. 1715 and 1735 cm-1). Concentration of themother liquor under vacuum yielded the ' endo '-bromo-lactone acid (v,,,, 17 15 and 1815 cm-l) .6-exo, 6-endo-Dibromo- 1-( 1,3-dioxan-2-yE)-7-oxabicyclo[2.2.l]hepta-2,3-dicarboxyZic anhydride (4a)was obtained from the mixture (la and b) or from ( l a ) ;yield 97%; m.p. 235-236" (Found: C, 35.1; H, 3.1; Br,Cl,H,,O, requires C, 61.2; H, 6-15y0].Dibromide adducts1975 61138.6.Cl,Hl,Br,O, requires C, 34.95; H, 2.9; Br, 38.8%);7 [(CD,),CO] 4.85 (lH, s, acetal H), 5.0 (lH, s, H-4), 5.28 (lH,7.2 Hz, H-2), 6.0 (lH, d, J 7.2 Hz, H-3), 6.1-6.6 (4H, m,OCH,), 7.2-8-2 (lH, m, CH), and 8.5br (lH, d, CH). Thecorresponding 2-ethyl ester had m.p. 165-167" (Found: C,36-5; H, 4-0; Br, 34-6. Cl,Hl,Br,O, requires C, 36.7; H,3-95; Br, 34.9%).5-exo,6-endo-Dibromo- 1-(4-methyZ-1,3-dioxaut-2-yZ)-7-oxa-bicyclo[2.2.l]heptane-2,3-dicarboxylic anhydride (4b) was ob-tained from ( l b ) ; m.p. 207-209" (decomp.); 96% yield(Found: C, 36-7; H, 3-4; Br, 37.2. Cl,Hl,Br,O, requiresC, 36.65; H, 3.3; Br, 37.5y0), J2,3 3.1, J 5 , , 7.1 Hz.5-exo,6-endo-Dibromo-l-( 5-ethyl-5-methyl- 1,3-dioxan-2-yZ)-7-oxabicyclo[2.2.l]heptane-2,3-dicarboxylic anhydride (4h),obtained from (lh), %had m.p.233-234" (decomp.) ; 98%yield (Found: C, 39-6; H, 3.9; Br, 35.2. C15H18Br206requires C, 39-6; H, 3-95; Br, 35.21y0).5-exo, 6-endo-Dibromo- 1- (5,5-diethyl- 1,3-dioxan-2-yZ) - 7-oxabicycZo[2.2.l]heptane-2,3-dicarboxylic anhydride (44 , ob-tained from (li) or the isomeric mixture, had m.p. 206-208"(Found: C, 39.5; H, 4-3; Br, 33.0. Cl,H,,Br20, requiresC, 39.7; H, 4.15; Br, 33.1%). The corresponding diethylester had m.p. 243-244" (decomp.) (Found: C, 44-1; H,5.7; Br, 29.3. C,,H,,Br,O, requires C, 44.3; H, 5.55; Br,29.5%) ; vmx. 1735 cm-1 (CO ester), J2,3 3-3, J S a 6 9.4 Hz.Diethyl 5-exo, 6-endo-Dibromo- 1-(4,6-dimethyZ- 1,3-dioxan-2-yl)-7-oxabicycZo[2.2.l]heptane-2,3-dicarboxylate, obtainedfrom (lc) (yield 67y0), had m.p.161-163" (Found: C, 42.0;H, 5.0; Br, 30.9. C1,H,,Br2O, requires C, 42.1; H, 5-05;Br, 31.2%).The monoethyl ester of 5-exo, 6-endo-dibromo- 1-( 6-iso-propyl-5,5-dimethyl- 1,3-dioxan-2-yl) -7-oxabicyclo[2.2. I] -heptane-2,3-dicarboxylic acid, obtained from (lg) (yield78%), had m.p. 144-145O (Found: C, 43.0; H, 5.1; Br,30-0. Calc. for C,,H,,Br,O,: C, 43.2; H, 5-3; Br, 30*3~0),v , , ~ ~ 1712 (CO acid) and 1738 cm-1 (CO ester), T [(CD,),CO]0.8 (lH, s, CO,H), 4.8 (lH, s, acetal H), 4.95 (lH, s, H-4),d, J 3.0 Hz, H-5), 6.6 (lH, d, J 3.0 Hz, H-6), 5.75 (lH, d, J5.17 (lH, d, J 3.6 Hz, H-5), 5-57 (lH, d, J 3.6 Hz, H-6), 5.75(lH, d, J 7.2 Hz, H-2), 5.97 (lH, d, J 7.2 Hz, H-3), 5.85 (2H,q, J 6-8 Hz, MeCH,), 6.2-6.6 (2H, q, J 11.7 Hz, OCH,),6.85 (lH, d, J 3.6 Hz, OCH), ca.8.0 (IH, m, CH), 8.75 (3H,t, J 6.8 Hz, CH,Me), 8.85 (3H, s, Me-ax), 9.2 (3H, s, Me-eq),and 9.0 (6H, d, J 6.75 Hz, Me,C).Bromo-lactone Acids (Esters) .-To a stirred mixture of theappropriate adduct (0.1 mol) and water (or an alcohol) (200ml) in an ice-salt bath, potassium hydroxide (0.15-0.21mol) in water (50 ml) was added. The solution was cooledto 0-5 "C and bromine was added dropwise with constantstirring until a faint colour persisted. Care was taken tomaintain the temperature of the mixture below 5 "C.Acidification with hydrochloric acid produced a crystallineprecipitate (7), which was collected, washed several timeswith water, and crystallized from ethanol. The bromo-lactone acids (esters) (5)-(8) were extracted from themother liquor with chloroform.The organic layer waswashed with aqueous 3% sodium hydrogen carbonate,aqueous 5% sodium thiosulphate, and water, then evapor-ated. The residue was crystallized from alcohol. Byfractional recrystallization from ethanol (or propan-2-01) theisomeric bromo-lactone esters were separated. Compounds(7) and (8) crystallized as fine needles, whereas (5) formedrhombohedra which melted without decomposition to aclear liquid. In contrast, (7) melts with complete decom-position.Methyl esters of the bromo-Zactone acids. Diazomethanewas distilled into an ethereal solution of the bromo-lactoneacid. After the reaction had ceased, the ether was boiled offand the solid recrystallized from ethanol.Speci-men 1H n.m.r.parameters for the four isomeric bromo-lactone esters (5)-(8) are given in Table 3. The i.r. spectrashowed v,,, 1730-1735 (CO ester) and 1800-1820 cm-l(CO lactone).MethyZ 5-exo-Bronzo-4- (1,3-dioxan-2-yl)-3-methoxycarbon-yZ-7-oxabicyclo[2.2.l]heptane-2,6-carbolactone (5a) was ob-tained from (2a) in 45% yield; m.p. 164165" (from ethanolas a second crop) (Found: C, 43.1; H, 4.2; Br, 21.9.Cl,H,5Br0, requires C, 43.0; H, 4-15; Br, 22.0%).5-exo-Bromo-3-carboxy- 1- ( 1,3-dioxan-2-yl) -7-oxabicycZo-[2.2.l]heptane-2,6-carboZactone (6a) was obtained from themixture of (la) and (2a) in 7.5% yield; m.p. 212-214"(from chloroform-ethanol as fourth crop) (Found: C, 41.7;H, 3.6; Br, 22.6.C12Hl,Br0, requires C, 41.25; H, 3.7;Br, 2%9y0).7-endo-Bromo- 1-( 1,3-dioxan-2-yl)-6-methoxycarbonyl-2-oxabicyclo[2.2.l]heptane-5,3-carbolactone (7a) was obtainedfrom (la) in 86y0 yield; m.p. 238-239" (decomp.) (fromethanol) (Found: C, 43.2; H, 4.2; Br, 21.9%).5-exo-Bromo-3-ethoxycarbonyl-4- (4-methy Z- 1,S-dioxan- 2-yl)-7-oxabicyclo[2.2.l]heptane-2,6-carbolactone (5b) was ob-tained from the mixture of (lb) and (2b) in 32% yield; m.p.139-141' (from ethanol as a second fraction) (Found: C,45-9; H, 4.9; Br, 20.5. C15Hl,Br0, requires C, 46.05;€3, 4-85; Br, 20.46y0).7-endo-Bromo-6-carboxy- 1-(4-methyl-1,3-dioxan-2-y1)-2-oxabicycZo[2.2.l]heptane-5,3-carbolactone (7b) was obtainedfrom the complex of maleic anhydride with (lb) in 41%yield; m.p.182-183" (from methanol) (Found: C, 43.0;H, 4.3; Br, 21.8%).7-endo-Bromo-6-ethoxycarbonyl-3- (4-methyl- 1,3-dioxan-2-yZ)-2-oxabicyclo[2.2.l]heptane-5,3-carbolactone (8b) was ob-tained from the complex of maleic anhydride with (lb) in12% yield; m.p. 220-221" (from ethanol as a second frac-tion) (Found: C, 46.1; H, 4-7; Br, 20.5%).5-exo-Bromo-4- (4,6-dimethyl- 1,3-dioxan-2-yl)-3-methoxy-carbonyl-7-oxabicyclo[2.2.l]heptane-2,6-carboZactone (5c) wasobtained from the mixture of (lc) and (2c) in 23% yield;m.p. 183-184" (from ethanol as a second fraction) (Found:C, 46-1; HI 5.0; Br, 20.2y0).7-endo-Bromo- 1-(4,6-dimethyZ- 1,3-dioxan-2-yZ)-6-ethoxy-carbonyl-2-oxabicycZo[2.2.1] heptane-5,3-carbolactone (7c) wasobtained from (lc) in 71% yield; m.p.229-231O (fromethanol) (Found: C, 47.2; H, 5.2; Br, 19.6. C,,H,,BrO,requires C, 47.4; H, 6.2; Br, 19.75y0).5-exo-Brorno-3-ethoxycarbonyl-4-(4,4,6-trirnethyZ-l,3-di-oxan-2-yZ)-7-oxabicyclo[2.2.l]he~tane-2,6-carbolactone (5d)was obtained from the mixture of (Id) and (2d) in 18% yield;m.p. 176-177" (from ethanol) (Found: C, 48.5; H, 5.6;Br, 18.8. C,,H,,BrO, requiresc, 48.7; H, 5.5; Br, 19.05%).7-endo-Bromo-6-methoxycarbonyl-3- (4,4,6-trimethyZ- 1,3-di-oxan-2-yl) -2-oxabicycZo[2.2.l]he~tane-5,3-carboZactone (8d)was obtained from (Id) in 71% yield; m.p. 208-209O (frommethanol) (Found! C , 47.2; H, 5.2; Br, 19.1%).7-endo-Bromo-6-ethoxycarbonyl- 1- (4,5,6-trimethyZ- 1 , 3-dz-oxan-2-yl)-2-oxabicyclo[2.2.l]he~tane-5,3-carboZactone (7e)was obtained from (le) in 24% yield; m.p.190-191"(decomp.) (from ethanol) (Found: C , 48.6; H, 5.6; Br,Spectral data for the isomeric bromo-Zactone esters.19*0y0)612 J.C.S. Perkin I7-endo-Bromo-6-methoxycarbonyl-3- (4,5,6-trimethyZ- 1,3-di-oxan-2-yJ)-2-oxabicycZo[2.2.l]he~tane-B, 3-carbolactone (8e)was obtained from (le) in 15% yield; m.p. 214-215" (fromethanol) (Found: C, 47-2; H, 5.1; Br, 19.6%).7-endo-Bromo- 1-( 6-isopropyZ-5,5-dimethyZ- 1,3-dioxan-2-yZ)-6-methoxycarbonyl-2-oxabicycZo[ 2.2.13 heptane- 5,3-carbo-Zactone (7g) was obtained from (lg) in 18% yield: m.p. 179-181' (from ethanol as a second crop) (Found: C, 49.9; H,5.9; Br, 18.2. C,,H,,BrO, requires C, 49.9; H, 5-75; Br,18.45y0).7-endo-Bromo-3- (6-isopropyZ-5, 5-dimethyl- 1,3-dioxan-2-yl)-&methoxycarbonyZ-2-oxabicycZo[2.2.1] heptane- 5,3-carbo-Zacfone (8g) was obtained from (lg) in 72.5y0 yield; m.p.228-229' (from propan-2-01) (Found: C, 49.9; H, 5.8;Br, 18.3%).5-exo-Bromo-4-( 5,5-diethyl-lI3-dioxan-2-yl)-3-methoxy-ca~bonyZ-7-oxabicyclo[2.2.l]heptane-2,6-carboZactone (5i) wasobtained from the mixture of (li) and (2i) in 43% yield;m.p. 166-168' (from ethanol) (Found: C, 48.6; H, 5.6;Br, 19.0%).7-endo-Bromo- 1-( 5,5-diethyl- 1 3-dioxan-2-yl) -6-methoxy-carbonyl-2-oxabicycZo[2.2.l]he~tane-5,3-carbolactone (74 wasobtained from (li) in 84% yield; m.p. 207-209' (fromethanol) (Found: C, 48.5; H, 5.4; Br, 19.4y0).5-exo-Bromo-4-(5,5-dimethyZ- 1,3-dioxan-2-yl)-3-melhoxy-carbonyl-7-oxabicyclo[2.2.l]he~tane-2,6-ca~bolactone (5f) wasobtained from the mixture of (If) and (2f) in 41% yield;m.p. 164-165" (from methanol) (Found: C, 46.0; H, 5.0;Br, 20.2%).5-exo-Bromo- 1-(5,5-dimethyl- 1,3-dioxan-2-yZ)-3-ethoxy-carbonyl-7-oxabicycZo[2.2.1] heptane-2,6-carbolactone (6f) wasobtained from the mixture of (If) and (2f) in 11% yield;m.p. 150-151' (from ethanol as a fourth crop) (Found:47-3; H, 5.2; Br, 19.5%).7-endo-Bromo- 1-(5,5-dimethyZ- 1 , 3-dioxan-2-yE)-6-methoxy-carbonyZ-2-oxabicycZo[2.2.1] heptane-5,3-carboZactone (7f) wasobtained from (If) in 86% yield; m.p. 223-224' (fromethanol) (Found: C, 46.1; H, 5.0; Br, 20.0y0).carbonyl-2-oxabicycZo[2.2.l]he~tane-5,3-carboZactone (8f) wasobtained from (If) in 13-5y0 yield; m.p. 170-171" (fromethanol as a second crop) (Found: C, 46.2; H, 5.1; Br,20.4%). The n.m.r. data of compounds (5f), (6f), (7f), and(8f) are given in Table 3.I acknowledge financial support by the Institute ofPolymer Chemistry, Polish Academy of Sciences.[4/1639 Received, 6th August, 197417-endo-Bromo-3-( 5,5-dimethyl- 1,3-dioxan-2-y1) -6-methoxy
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