Preparation of dithiadiazafulvalene precursors: 2-piperidino-2,3-dihydro-1,3-thiazoles or 2-unsubstituted 2,3-dihydro-1,3-thiazoles from the reduction of the corresponding 2-piperidino mesoionic thiazoles

摘要

1469J. CHEM. SOC. PERKIN TRANS. I 1994 Preparation of Dith iad iazaf u Iva lene Precursors: 2-Pi perid ino-2.3-d i hyd ro- 1.3-thiazoles or 2-Unsubstituted 2.3-Dihydro-I ,3-thiazoles from the Reduction of the Corresponding 2-Piperidino Mesoionic Thiazoles Mohammed Bssaibka Albert Robert *ra and Abdel Aziz Souizib a Laboratoire de Chimie Structurale, URA CNRS 704, Campus de Beaulieu, 35042 Rennes Cedex, France Laboratoire de Synthese Organique, Faculte des Sciences de Kenitra, Maroc Depending on the experimental conditions, either the 2-piperidino-3-aryl-4-alkylthio-5-aryl-or -alkyl- 2,3-di hydro- 1.3-thiazoles 8 or the 2-unsubst ituted 3-aryl-4-al kylthio-5-aryl- or -alkyl-2,3-di hydro- 1.3-thiazoles 10 have been prepared starting from mesoionic 5-alkyl- or 5-aryl-2-piperidino-1,3-thiazole-4-thiolates 6.After alkylation of the mesoionic compound, the best conditions to isolate these two dihydrothiazoles were established from a mechanistic study of the reduction. Compound 8 is known to give dithiadiazafulvalenes' through its thiazolium tetrafluoroborate salts. We show here that such salts can also be obtained from 10. Although dithiadiazafulvalenest (DTDAF) are very good donors, their sensitivity to air is probably the reason why they have been so little We recently described a synthesis of DTDAF using mild reaction conditions and in which DTDAF was trapped as a charge transfer salt.' The key step of the reaction was the formation of DTDAF from thiazolium salt 12 obtained through the 2-amino-2,3-dihydro- 1,3-thiazole 8.During the preparation of these 2-amino-2,3- dihydrothiazoles 8, through the reduction of mesoionic thia- zoles 6 it appeared that contrary to what was observed with the corresponding 1,3-dithi0les,~ the major products obtained were the 2-unsubstituted dihydrothiazoles 10. We decided to study the mechanism of this reduction in order to design the best synthetic route to compounds 8 or 10. To us, such a study seemed to be of interest since, to the best of our knowledge, the only reported 2,3-dihydrothiazoles unsubstituted on the 2 position are dihydrothiamine (the reduced form of vitamin B,) and the derived phosphates.' Furthermore, it can be discounted that, like the corresponding 1,3-dithioles, the dihydrothiazoles 10 will be amphoteric derivatives giving, according to the experimental conditions, either 1,3-thiazolium anions or 1,3- thiazolium cation^,*^^ which could be of particular interest for DTDAF ~ynthesis.'~We report here the mechanism of NaBH, reduction of mesoionic thiazoles 6, and described the best way to prepare either compounds 8 or 10.We have already shown that alkylation of a mesoionic dithiole 1 gives the dithiolium salt 2, which is quantitatively reduced by NaBH, to give a 2-aminodithiole 3. Tetrafluoro-boric acid converts 3 into the dithiolium salt 4 which is reduced by lithium aluminium hydride to give the 2-unsubstituted dithiole 5 (see Scheme l).' When mesoionic thiazoles 6 were the starting materials, alkylation followed by NaBH, reduction gave the 2-unsubsti- tuted dihydrothiazoles 10 directly.Only with R3= p-NO,-CsH, was the major product the corresponding 2-aminodihy- drothiazole 8, which was then easily reduced in situ under acidic conditions to give quantitatively the corresponding dihydro- thiazole 10. It seemed likely that the 2-aminodihydrothiazole 8 and the thiazolium salt 9 were intermediates leading to the dihydrothiazole 10 (see Scheme 2). However, in contrast to the observations with the dithiole series, the 2-aminodihydro- thiazoles 8 with R3# p-N02C,H, were unstable even under non-acidic conditions. Dithiadiazafulvalene = 2,2'-bi( 1,33HJ-thiazol-2-ylidene). 1' 2 31 iii t RgR'3: -sPip = piperidino i" WR2 YSw;H 5 4 Scheme 1 Reagents: i, R2X;ii, NaBH,, EtOH; iii, HBF,; iv, LiAIH4 The following experiments were designed in order to confirm the postulated mechanism of Scheme 2: (a) In order to establish that compounds 8 and 9 were in equilibrium we treated compound 7with NaBH, in CH,Cl,, in the presence of a large excess of piperidine to give the 2-piperidinodihydrothiazoles8 quantitatively.Similarly, in the presence of an excess of morpholine, the sole product isolated, in good yield, was the corresponding 2-morpholinodihydro- thiazole 11 (see Scheme 3). It was also shown that the reaction of the 2-piperidinodihydro- 1,3-thiazole 8d with morpholine gave the corresponding 2-morpholinodihydro- 1,3-thiazole 11 quantitatively. (b)In order to establish that compound 8 is an intermediate leading to compound 10, we prepared the former according to the experimental conditions shown in Scheme 3 (excess of piperidine) and subjected it to the experimental conditions described in Scheme 2 to give compound 10 quantitatively.(c) It was also possible to prove in one case that compound 9 is a likely intermediate which is then reduced to give compound 10. The reduction of the thiazolium iodide 7a according to the procedure described in Scheme 2 gave 10a together with a small quantity of the thiazolium iodide 9a which was isolated and characterized. The NaBH, reduction of 9a gave 10a quantitatively. Since the 2-unsubstituted dihydrothiazoles 10 were easily prepared, it was also of interest to prove their usefulness for the preparation of thiazolium tetrafluoroborate salts 12 which are key starting materials for the synthesis of DTDAF.When the dihydrothiazoles 10 were treated with a stoichiometric quantity J. CHEM. soc. PERKIN TRANS. 1 1994 Conclusions While mesoionic 2-piperidino- 1,3-dithioles 1 are alkylated i SYN-R3-YN-" Pip Pip 6 7 1 0a-c Ls QJ iii Pip = piperidino R' R' Aiii R'HSR2 Pip HsxN-R3 o--/ lld Pip = piperidino Scheme 3 Reagents: i, R2X; ii, NaBH,, CH2C12; iii, excess of piperidine; iv, excess of morpholine 10 12 Scheme 4 Reagents: i, Ph,CBF,, CH2C12 of triphenylcarbenium tetrafluoroborate, the corresponding thiazolium salts 12 were isolated and characterized (51-88) (see Scheme 4).and then reduced by NaBH, in EtOH to give exclusively the 2-piperidinodithioles 3, the corresponding mesoionic 2-piperidino-l,3-thiazoles6 lead to good yields of the 2-unsubstituted dihydrothiazoles 10 under the same conditions. A study of the mechanism of this reaction has allowed us to identify the best experimental conditions (CH2C12 solvent and excess of piperidine) to obtain good yields of the 2-piperidinodihydrothiazoles 8. We have also shown that the dihydrothiazoles 10 are good starting materials for the perparation of the thiazolium salts 12. Experimental 'H NMR spectra were recorded at 80 MHz on a Bruker WP 80 spectrometer and 13C NMR spectra at 75 MHz on a Bruker AM 300 spectrometer with tetramethylsilane as internal reference.Mass spectra were determined with a Varian Mat 3 1 1 Spectrometer. M.p.s were taken with a Kofler hot stage apparatus. Ether refers to diethyl ether. Mesoionic Thiazoles 6.-For R' = aryl, we prepared the derivatives according to ref. 10. For R' = Me, the following method was employed. Phenyl isothiocyanate (40 mmol) or p-nitrophenyl isothiocyanate (3 mmol) was added to a suspension of the dithiole 1 (R' = Me) (2 mmol) in dry C6H6 (100 cm3) and the mixture was refluxed for 15 h (R3 = Ph) or 8 h (R3 = p-N02C6H,). Evaporation of the solvent and addition of dry ether (100 an3)to the residue gave a precipitate which was filtered off and recrystallized from MeCN; 6 (R' = Me, R3 = Ph): 63, m.p. 146 "c; d,(CDCl,) 1.10 6 H, m, N(CH2),, 3.10 4 H, m, N(CH,),, 2.39 (3 H, s, SMe) and 7.49 (5 H, m, ArH); 6 (R' = Me, R3 = p-N02C6H4): 72, m.p.195 "C (MeCN) (Found: C, 13.8; H, 5.0; N, 12.4. C,,H,,- N202S requires C, 13.71; H, 5.11; N, 12.13); G,(CDCl,) 1.12 6 H, m, N(CH,),, 3.10 4 H, m, N(CH,),, 2.39 (3 H, s, SMe), 7.62 and 8.42 (4 H, AA'XX', p-N02C6H,). Thiazolium Cations 7a, 7b,7d, 7e and 7g-i.-R2X (X = Br or I) (25 mmol) was added to a suspension of compound 6 (5 mmol) in CH2Cl, (20 an3).The mixture, which became homogeneous, was left at room temperature for 12 h after which it was evaporated. For R3 = p-N02C6H4, addition of EtOH to the mixture precipitated the thiazolium salt 7 which was filtered off and washed with EtOH. The other salts 7 were obtained as oils which were carefully washed with dry ether and directly used for further reactions.7a (X = I), m.p. 200deg;C (EtOH) (Found: C, 43.95; H, 3.7; N, 7.3; C1, 6.2; I, 22.1. C2,H2,C1IN3O2S2 requires C, 43.80; H, 3.55; N, 7.27; Cl6.23; I, 22.19); G,(CDCl,) 20 (4, SCH,), 22, 24, 54 tm, N(CH,),, 130 (m, C-5), 133 (9, C-4), 168 (m, C-2), 125, 127, 129, 130.9, 131, 136, 142 and 149 (aromatic C). Yields and 'H NMR data for salts 7 are summarized in Table 1. Thiazolium Cations 7c and 7f.-BrCH,C6F, (5 mmol) was added to a suspension of compound 6 (5 inmol) in CH2Cl, (20 cm3) and the reaction mixture boiled for 12 h. Evaporation of the mixture gave the salt 7 (X = Br) as an oil, which was washed with dry ether and used without further purification. Yields and 'H NMR data for salts 7are summarized in Table 1.2-Piperidino-2,3-dihydro-1,3-thiazoles8a-amp; (R3= p-NO,-C,H,).-Sodium borohydride (250 mg) was added to a suspension of compound 7 (5 mmol) in EtOH (20 cm3) at 0 "C. After 3 min, the product 8 was filtered off and recrystallized from MeCN; 8a (Found: C, 56.35; H, 4.95; N, 9.4; C1, 8.00. C,,H2,C1N,0,S2 requires C, 56.30; H, 4.95; C1,7.91; N, 9.38); 8b (Found: C, 61.7; H, 5.85; N, 9.9. C2,H2,N,02S2 requires J. CHEM. SOC. PERKIN TRANS. I 1994 Table 1 Physical data for 2-piperidino-I ,3-thiazolium salts 7 Yield () N(CH2)s R2 R' and R'X ~~~ ~ ~ ~ a I 95 1.65 (m, 6 H), 3.50 (m, 4 H) 2.00 (s, 3 H) 8.50 (s, 4 H), 7.55 (AB, 4 H) b I 94 1.65 (m, 6 H), 3.50 (m, 4 H) 2.00 (s, 3 H) 2.45 (s, 3 H), 7.50-8.50 (m, 9 H) c Br 97 1.67 (m, 6 H), 3.53 (m, 4 H) 3.58 (s, 2 H) 2.45 (s, 3 H), 8.48 (s, 4 H) d I 98 1.62 (m, 6 H), 3.47 (m, 4 H) 1.97 (s, 3 H) 7.67 (m, 9 H) e Br 96 1.62 (m, 6 H), 3.53 (m, 4 H) 0.85 (t, 3 H), 2.35 (q,2 H) 7.65 (m, 9 H) f Br 95 1.67 (m, 6 H), 3.58 (m, 4 H) 3.70 (s, 2 H) 7.65 (m,9 H) g I 97 1.60 (m, 6 H), 3.50 (m, 4 H) 1.97 (s, 3 H) 2.40 (s, 3 H), 7.00-8.00 (m, 9 H) h Br 96 1.60 (m, 6 H), 3.50 (m, 4 H) 0.85 (t, 3 H), 2.30 (q,2 H) 2.35 (s, 3 H), 7.12-7.92 (m, 9 H) i I 93 1.65 (m, 6 H), 3.45 (m, 4 H) 2.05 (s, 3 H) 2.57 (s, 3 H), 7.67 (m, 5 H) Table 2 Physical data for 2-piperidino-2,3-dihydro-1,3-thiazoles8 4dCDCld M.p./( T/"C) Yield () N(CH,), R2 H R' and R3 ~ ~ ~ ~ ~~~ ~~~~~~~~ a b c d 182 172 132 128 80 82 60 62 1.55 (m, 6 H), 2.60 (m, 4 H) 1.55 (m, 6 H), 2.62 (m, 4 H) 1.55 (m, 6 H), 2.55 (m, 4 H) 1.50 (m, 6 H), 2.55 (m, 4 H) 1.90 (s, 3 H) 1.87 (s, 3 H) 3.75 (s, 2 H) 1.85 (s, 3 H) 6.00 (s, I H) 5.98 (s, 1 H) 5.95 (s, 1 H) 5.85 (s, 1 H) 7.45 (AB, 4 H), 2.35 (s, 3 H), 7.33 (AB, 4 H) 2.15 (s, 3 H), 7.20-7.62 (m, 9 H) 7.55, 8.23 (AA'XX', 4 H) 7.55, 8.20 (AA'XX', 4 H) 7.30, 8.10 (AA'XX', 4 H) g 155 50 1.52 (m, 6 HI, 2.60 (m, 4 H) 1.90 (s, 3 H) 5.87 (s, 1 H) 2.30 (s, 3 H), 7.1CL7.30 (m, 9 H) Table 3 Physical data for thiazoles 10 M.p./(T/OC) Yield rA) R2 CH2 R' and R3 a 166 92 2.00 (s, 3 H) 5.25 (s, 2 H) 7.48 (AB, 4 H), 7.25,8.20 (AA'XX', 4 H) b 172 90 1.97 (s, 3 H) 5.23 (s, 2 H) 2.37 (s, 3 H), 7.36 (AB, 4 H), 7.23,8.20 (AA'XX', 4 H) c 120 70 3.67 (s, 2 H) 5.12 (s, 2 H) 1.97 (s, 3 H), 6.98, 8.13 (AA'XX', 5 H)d 124 88 2.00 (s, 3 H) 5.12 (s, 2 H) 7.00-7.62 (m, 9 H) e 70 82 1.07(t,3H),2.47(q,2H) 5.15(s,2H) 7.00-7.65 (m, 9 H) f 139 95 3.70 (s, 2 H) 5.20 (s, 2 H) 7.28-8.00 (m, 9 H) g 103 94 2.00 (s, 3 H) 5.12 (s, 2 H) 2.35 (s, 3 H), 7.05-7.60 (m, 9 H) i Oil 85 2.05 (s, 3 H) 5.02 (s, 2 H) 2.15 (s, 3 H), 7.00-7.35 (m, 5 H) C, 61.80; H, 5.89; N, 9.83); amp;(Found: C, 51,l; H, 3.9; N, 8.1; F, (500 mg) was slowly added to a suspension of compound 7 (5 18.35.C22H2,F5N302S2requires C, 50.97; H, 3.95; N, 8.00; F, mmol) in EtOH (20 cm3) after which the reaction mixture was 18.40). Yields, m.p.s and 'H NMR data for 2-piperidino-2,3- stirred for 5 min and then treated with HCl(6 mol dmP3; 4 cm3).dihydro-1,3-thiazoles8 are summarized in Table 2. After 10 min, the precipitate was filtered off and recrystallized from EtOH. 10a (Found: C, 52.55; H, 4.0; C1, 9.8; N, 7.7. 2-Piperidino-2,3-dihydro-l,3-thiazoles8d and 8g (R3# p-C16H13C1N202S2 requires C, 52.67; H, 3.59; N, 7.68; C1, NO2C,H4).-To a solution of 7 (5 mmol) in CHzC12 (25 an3), 9.72); lob (Found: C, 59.38; H, 4.7; N, 8.1. Cl7Hl6N2OZS2 piperidine (25 mmol) and sodium borohydride (10 mmol) were requires C, 59.15; H, 4.73; N, 8.22); 1Oc (Found: C, 47.0; H, added, successively. The reaction mixture was stirred for 20 min 2.55; N, 6.45; F, 21.9. C,,H1,F5N2O2S2 requires C, 46.91; H, at room temperature and washed with NaOH (1 mol dmP3; 2.65; N, 6.51; F, 21.77).Yields, m.p.s and 'H NMR data for 5 x 25 cm3). The organic phase was dried (Na2S04) and dihydrothiazoles 10 are summarized in Table 3. concentrated. Compound 8, precipitated by addition of ether (25 cm3) was recrystallized from EtOH; 8d (Found: C, 62.25; 2,3-DihydrothzizzoZes 1Od-i (R3# p-NO2C,H4).-NaBH4 H, 5.6; N, 7.1; C1,9.1; M', 402.0990. C2,H2,CIN2S2 requires (250 mg) was added to a solution of compound 7 (5 mmol) in C, 62.59; H, 5.75; C1,8.80; N, 6.95; M,402.09911); G,(CDCI,) EtOH (25 an3).Compound 10 either formed a precipitate in 16 (q, SCH,), 24,25,46 tm, N(CH2),, 93 (d, C-2), 117 (q, C- which case it was filtered off and recrystallized from EtOH, or 4), 132.2 (t, C-5), 122, 124, 126, 128, 128.5, 131, 132.7 and 145 the mixture was diluted with water (75 cm3) and extracted with (aromatic C); m/z 402 (M') and 318 (M -N(CH,),+}.8g ether (2 x 25 cm3). The extract was then washed with water, (Found: C, 69.1; H, 6.85; N, 7.3. C22H,,N,S, requires C, 68.99; dried (Na2S04) and evaporated to give an oily residue which H, 6.93; N, 7.41). Yields, m.p.s and 'H NMR data for was sufficiently pure (NMR analysis) to use without further 2-piperidino-2,3-dihydro-1,3-thiazoles 8 are summarized in purification. 1Od (Found: C, 59.9; H, 4.55; Cl, 10.95; N, 4.5; Table 2. M', 319.0253. Cl6H1,C1NS2 requires C, 60.10; H, 4.38; C1, 11.09; N, 4.38; M, 319.02562); m/z 319 (M') and 155 (p-2,3-Dihydrothiazoles 1Oa-c (R3 = p-N02C,H4).-NaBH4 C1C6H4CS+); G,-(CDC13) 17 (9, SMe), 60 (t, c-2), 129.6 (m, Table 4 Physical data for thiazolium tetrafluoroborate salts 12 M.p./(T/OC) Yield () R2 12a 12c 12d 12f 1 12i 132(EtOH) 90 145(EtOH) 260 98(EtOH) Oil 72 70 88 56 85 51 2.05 (s, 3 H) 3.83 (s, 2 H)" 1.97 (s, 3 H) 3.67 (s, 2 H)" 1.95 (s, 3 H) 2.05 (s, 3 H) " 'H NMR in CD,CN.C-4), 131 (t,C-5), 122.6, 123.5, 124, 128.1, 128.9, 131.2, 133and 145 (aromatic C); 10e (Found: C, 60.8; H, 4.6; Cl, 10.6; N, 4.1. C,,H,,ClNS, requiresC, 61,17; H,4.79; C1,10.6;N,4.20); 10f (Found: C, 54.4; H, 2.7; C1,7.2; N, 2.8. C,,H13ClF,S, requires C, 54.38; H, 2.70; Cl, 7.30; N, 2.70); 1 (Found: C, 68.2; H, 5.7; N, 4.7. C,,H,,NS, requires C, 68.05; H, 5.81; N, 4.73). The obtained oil 1 was used directly for further reactions without purification.Yields, m.p.s and 'H NMR data for the dihydrothiazoles 10 are summarized in Table 3. Thiazolium Salts 12.-Triphenylcarbenium tetrafluoroborate (4 mmol) was added to a solution of the dihydrothiazole 10 (4 mmol) in CH,Cl, (30 cm3) at 0 "C. After the reaction mixture had been stirred for 2 h it was diluted with anhydrous ether (50 cm3) to precipitate the thiazolium salts 12. These were filtered off and recrystallized from EtOH. 12a (Found: C, 42.8; H, 2.7; N, 6.5; Cl, 7.4. C,,Hl,BC1F,02S, requires C, 42.64; H, 2.68; Cl, 7.87; N, 6.22); 12d (Found: C, 47.1; H, 3.1; C1, 8.6; N, 3.4. C,,Hl3BC1F4NS2 requires C, 47.37; H, 3.23; C1, 8.74; N, 3.45); Gc(CDC1,) 18 (q, SMe), 137.2 (m, C-5), 144 (q, C-4), 152 (d, C-2), 126.3, 126.5, 129.6, 129.9, 131.3, 131.7, 137.3 and 140 (Arc); 12g (Found: C, 53.0; H, 4.2; N, 3.6.C17H,,BF,NS, requires C, 52.89; H, 4.25; N, 3.70). Thiazolium salts 12c and 12f were insufficiently stable to be purified, being easily thermolysed during recrystallization from EtOH to give the corresponding DTDAFs. The oil 12i obtained was directly used for further reactions without purification. Yields, m.p.s and 'H NMR data for thiazolium salts 12 are summarized in Table 4. Mechanistic Study.-Equilibrium between 8d and 9d: Form- ation of 2-Morpholino-2,3-dihydro-1,3-thiazole11 (R' = p-C1C6H4, R2 = Me, R3 = C,H,). Morpholine (20 mmol) was added to a solution of 2-piperidino-2,3-dihydro-1,3-thiazole8d (2 mmol) in CH,Cl, (10 cm3). The reaction mixture was stirred for 30 h at room temperature and then washed with water (3 x 20 cm3) dried (Na2S0,) and evaporated.Addition of ether (10 cm3) to the residue precipitated compound 11(R' = p-C1C6H4, R2 = Me, R3 = C6H5) which was recrystallized from MeCN (9379, m.p. 145 "C (Found: C, 59.8; H, 5.2; C1,8.8; N, 7.1. C,oH,,CIN,OS, requires C, 59.31; H, 5.23; C1, 8.75; N, 6.92); amp;(CDC13) 1.94 (3 H, S, SCH,), 2.69 4 H, m, N(CH,),O, 3.80 4H, t, N(CH,),O, 5.88 (1 H, s, H) and 7.16- 7.56 (9 H, m, aromatic H); GC(CDC1,) 16 (q, SCH,), 45.66 tm, N(CH,),O, 92 (d, C-2), 117 (9,C-4), 132 (t, C-5), 123, 125, 126, 128.1, 128.7, 131, 133 and 145 (aromatic C). Isolation of the Intermediate 9a. After isolation of the dihydrothiazole 10a according to the process described above, refrigeration of the filtrate obtained for 48 h, precipitated J.CHEM. SOC. PERKIN TRANS. 1 1994 R' and R3 H 7.60 (AB, 4 H), 7.85,8.48 (AA'XX', 4 H) 9.97 (s, 1 H) 2.60 (s, 3 H), 7.83, 8.48 (AA'XX', 4 H)" 9.97 (s, 1 H)" 7.37-7.70 (m, 9 H) 9.80 (s, 1 H)7.60-7.75 (m, 9 H)" 10.00 (s, 1 H)" 2.40 (s, 3 H), 7.20-7.62 (m, 9 H) 9.85 (s, 1 H)2.70 (s, 3 H), 7.15-7.55 (m, 5 H) 9.65 (s, 1 H) compound 9a. This was filtered off and recrystallized from EtOH (5), m.p. 188 "C (Found: C, 39.1; H, 2.6; C1,6.8; I, 25.3; N, 5.7. C,,Hl,C1IN2O,S, requires C, 39.16; H, 2.46; Cl, 7.22; I, 25.86; N, 5.70). GH(CDC1, and CF,CO,H); 2.08 (3 H, s, SCH,), 7.66 (4 H, AB, p-ClC,H,), 7.87, 8.53 (4 H, AA'XX', p- NO,C,H,) and 10.13 (1 H, s, CH); G,(CDCl, and CF,C02H) 18 (9, SCH,), 140 (tq, C-5), 145 (9, C-4), 159 (d, C-2), 125, 125.5, 128, 130.3, 130.4, 139, 140.5 and 150(ArC).Preparation of Compound 10d from Compound 8d. Sodium borohydride (50 mg) was added to a solution of 8d (1 mmol) in EtOH (25 cm3). The reaction mixture was stirred for 2 min, diluted with water (75 cm3) and extracted with ether (2 x 25 cm3). The combined extracts were washed, dried (Na,SO,) and concentrated. Addition of EtOH (5 cm3) to the residue precipitated compound 1Od which was recrystallized from EtOH (90), m.p. 124 "C; GH(CDC1,) 2.00 (s, 3 H, SMe), 5.12 (2 H, s, CH,) and 7.00-7.62 (9 H, m ArH). Preparation of Compound 10a from Compound 9a. Sodium borohydride (25 mg) was added to a suspension of compound 9a (0.5 mmol) in EtOH (5 cm3).The reaction mixture was stirred for 5 min after which the precipitate was filtered off, washed with EtOH and recrystallized from EtOH to yield 10a (90), m.p. 166 "C; dH(CDC13) 2.00 (3 H, S, SMe), 5.27 (2 H, S, CH,), 7.25,8.20 (4 H, AA'XX',p-NO,C,H,) and 7.47 (4 H, AB, P-clc, H4). References 1 M. Bssaibis, A. Robert, P. Le Magueres, L. Ouahab, R. Carlier and A. Tallec, J. Chem. Soc., Chem. Commun., 1993, 601. 2 J. Metzger, H. Larive, R. Dennilauler, R. Barelle and C. Gaurat, Bull. SOC.Chim. Fr., 1964,11,2857. 3 F. G.Bordwell and A. V. Satish, J. Am. Chem. SOC.,1991,113,985. 4 V. Goulle, S. Chirayil and R. P. Thummel, Tetrahedron Lett., 1990, 31, 1539. 5 G.V. Tormos, 0.J. Neilands and M. P. Cava, J. Org. Chem., 1992, 57, 1008. 6 A. Souizi and A. Robert, Tetrahedron, 1984,40, 1817. 7 H. Hirano, J. Pharm. SOC.Jpn., 1958,78,1387; G.E. Bonvicino and D. J. Hennessy, J. Am. Chem. SOC.,1957,79,6325. 8 J. Nakayama, K. Fujiwara and M. Hoshino, Bull. Chem. SOC.Jpn., 1976,49,3567. 9 D. Lorcy, M. P. Le Paillard and A. Robert, Tetrahedron Lett., 1993, 34,5289. 10 A. Souizi and A. Robert, Synthesis, 1982, 1059. Paper 3/07565F Received 24th December 1993 Accepted 1st March 1994