3.5 g of (S)-mandelic acid and 90 cm3 of a mixture of acetonitrile and water (99/1 by volume) are added to 7.15 g of (1RS,4aRS,7aRS)-4,4-diphenylperhydrothiopyrano[2,3-c]pyrrole 1-oxide. After stirring, the resulting solution is allowed to stand for 48 hours at room temperature. The crystals obtained are drained, washed with the acetonitrile-water mixture and then dried. The crystals are taken up in 200 cm3 of a boiling acetonitrile-water mixture and after filtering while still hot, the solution obtained is allowed to stand for 5 hours at room temperature. The crystals are drained, washed twice with 10 cm3 of acetonitrile and then dried. 1.5 g of (1R*,4aR*,7aR*)4,4-diphenylperhydrothiopyrano[2,3-c]pyrrole 1-oxide (S)-mandelate are obtained; [α]D 20 =-228°, (c =0 44; acetic acid). The filtrate is allowed to stand for 20 hours at room temperature, the crystals obtained are drained, washed twice with 5 cm3 of acetonitrile and then dried. 0.62 g of (1R*,4aR*,7aR*)-4,4-diphenylperhydrothiopyrano[2,3-c]pyrrole 1-oxide (S)-mandelate is obtained; [α]D 20 =-230°, (c =0.45; acetic acid).
