The pyroglutamic acid derivative 4 was converted through several steps into 2S, 3R, 4S- epoxyproline 8. Key steps of the reaction sequence were the stereoselective epoxidation of 4 to 5 and the chemoselective reduction of the amide group of 5 with concomitant transformation of the acetal moiety into the N-benzyl protecting group without oxirane ring opening. The air sensitive benzyl derivative was transformed to the stable N-Boc prolinol ...