Synthesis of (+)-Biotin

(+)-Biotin was synthesized from (3aS,4S,6aR)-1,3-dibenzyl-6-(3-methoxypropyl)-tetrahydrothieno[3,4-d]imidazol-2-one by chlorination with concentrated hydrochloride to give (3aR,8aS,8bS)-1,3-dibenzyl-2-oxodecahydroimadazo[4,5-c]thieno[1,2-a]thiolium chloride, which was subjected to condensation and ring opening, hydrolysis and decarboxylation with an overall yield of about 73%.