Formal syntheses of (−)-isoretronecanol, (+)-laburnine, and a concise enantioselective synthesis of (+)-turneforcidine

The synthesis of functionalized pyroglutamates 15 and 16 could be achieved by the application of recently developed diastereodivergent asymmetric Michael addition reaction of iminoglycinate 7 to ethyl γ -silyloxycrotonate with >98:<2 diastereoselectivity followed by hydrolysis and lactamization. Formal syntheses of (−)-isoretronecanol and (+)-laburnine as well as a concise enantioselective synthesis of (+)-turneforcidine could be achieved from functionalized pyroglutamates 15 or 16 .