Novel practical stereoselective synthesis of a bicyclic hydantoino-thiolactone as the key intermediate for production of (+)-biotin.

Bicyclic hydantoinothiolactone (1), as the key intermediate for production of (+)-biotin, has been efficiently and high-stereoselectively synthesized from the cheap starting material l-cystine via nine steps in 44% overall yield. In this new practical synthesis, there are two characteristic steps worthy of note. One step is TMSOTf-catalyzed efficient cyanation of (3 S ,7a R )-6-benzyl-5-oxo-3-phenyltetrahydro-1 H ,3 H -imidazo[1,5- c ]thiazol-7-yl acetate, the other step is DBU-catalyzed rapid isomerization of trans -isomer to cis -isomer of the bicyclic hydantoinothiolactone.