A novel approach to d-biotin from cysteine, which a utilizes the nitrate oxide To enolthioether double bond cyclization for the formation of C2-C3 of the thiophane ring and the incorporation of the 3-N in the biotin molecule, Is described. the cis relation of the n-butyl side chain and the sulfur in respect to isoxazolidine ring in the bicycle diastereomers And is characterized by an NMR signal For