15.8 g of (S)-(+)-mandelic acid and 750 cm3 of a mixture of acetonitrile and water (99/1 by volume) are added to 32.3 g of (1RS,4aRS,7aRS)-4,4-diphenylperhydrothiopyrano[2,3-c]pyrrole 1-oxide, followed by 5.0 cm3 of water. After making lukewarm, the solution obtained is allowed to stand for 48 hours at room temperature. The crystalline suspension is filtered, and the filtrate, concentrated to dryness, gives a meringue which is taken up in 200 cm3 of the boiling acetonitrile-water mixture. The solution obtained is allowed to stand for about 20 hours at room temperature. The crystals are drained, washed with acetonitrile, dried and then again taken up in 200 cm3 of an acetonitrile-water mixture (98/2 by volume). The resulting solution is allowed to stand for about 20 hours at room temperature. The crystals are drained and dried. 9.4 g of (1R*,4aR*,7aR*)-4,4-diphenylperhydrothiopyrano[2,3-c]pyrrole 1-oxide (S)-(+)-mandelate are obtained; [α]D 20 =+337°(c=0 45; acetic acid)
