m-Chloroperbenzoic acid → 3-Phenylsulfinyl-6-(1-hydroxyethyl)-7-oxobicyclo[3.2.0]-hept-2-en-2-carboxylic acid, diphenylmethyl ester

To a solution of 200 mg of 3-phenylthio-6-(1-hydroxyethyl)-7-oxobicyclo[3.2.0]hept-2-en-2-carboxylic acid, diphenylmethyl ester, in 15 mL of methylene chloride at -50° under nitrogen was added 90 mg of m-chloroperbenzoic acid in 3 mL of methylene chloride. The solution was stirred at -40° for 45 min and then warmed to room temperature over a 45 min period. The mixture was partitioned between methylene chloride and aqueous sodium sulfite. The organic layer was washed twice with bicarbonate, then brine, then dried over sodium sulfate and evaporated to dryness. The crude reaction product was purified by preparative thin layer chromatography two 20×20×0.2 cm silica gel plates, eluting with 5% methanol in methylene chloride, to afford 144 mg (69.6%) of 3-phenylsulfinyl-6-(1-hydroxyethyl)-7-oxobicyclo[3.2.0]-hept-2-en-2-carboxylic acid, diphenylmethyl ester, a diastereomeric mixture, as a colorless glass. IR (Nujol mull): 1780, 1710, 1600, 3400 cm-1 ; NMR (220 MHz; CDCl3 indicative of a 3:1 mixture of diastereoisomers at sulfur): δ 1.15 (3H, d, J=6.5, major isomer), 1.30 (3H, d, J=6.5, minor isomer), 2.3-3.0 (3H, m), 3.3-3.6(1H, m), 3.93 (1H, m, major isomer), 4.02 (1H, m, minor isomer), 4.52 (1H, m, minor isomer), 4.68 (1H, m, major isomer), 6.95 (1H, s), and 7.2-7.7 (15H, m). ##STR25##