Stereospecific transformations of steroidal 2,3-aziridines into substituted amino-thiols and ring-A fused heterocycles

1'-Acetyl-2ß,3ß-dihydro- and 1'-acetyl-2a, 3a-dihydro-androst-2-eno[2,3-b]azirin-17-one reacted with thiobenzoic S-acid to give the expected trans-diaxial ring-opened products, together with unexpected N-benzoyl-aziridines arising from transacylation. A mixed thioanhydride is postulated in a reaction pathway leading to the latter products. Classical trans-diaxial ring-opening and cyclization concepts were exemplified in ring-expansion reactions of aziridine derivatives to give chemospecific and stereoselective routes to a range of ring-A fused thiazolines and ring-A fused imidazo[2,1-b]thiazolines.