Synthesis of axially chiral vinylallenes, and their subsequent reactions : silver(I) catalyzed enantioselective diels-alder reaction and aerobic oxidation

Abstract

The pursuit of highly enantioselective reactions for the generation of complex organic molecules with point/axial chirality is everlasting for synthetic organic chemists. Axially chiral vinylallenes are important structural motifs present in natural products and are versatile chiral synthons attributed to axial-to-point chirality transfer. In this work, a series of axially chiral vinylallenes were successfully synthesized and two subsequent reactions: enantioselective silver(I) catalyzed Diels-Alder reaction and aerobic oxidation of vinylallenes, are described.

A series of axially chiral vinylallenes (up to 98% ee) were generated in good yields (up to 81%) by reacting chiral propargylamines in acetonitrile at 40°C. The optically active vinylallenes underwent silver-catalyzed cycloaddition with maleimines and azodicarboxylates in water at 40°C to form different cycloadducts as single diastereomers in excellent yields (up to 82%) with excellent enantioselectivity (up to 97% ee).

The chiral vinylallenes also underwent silver-catalyzed aerobic oxidation in acetonitrile at 40°C and light-induced oxidative cyclization via singlet oxygen in toluene at room temperature upon irradiation by a 300 W xenon lamp. For aerobic oxidation, a series of achiral cyclopentenones were synthesized in good yields (up to 79%). For light-induced oxidative cyclization via singlet oxygen, a new series of chiral 2H-pyranones were synthesized in excellent yields (up to 98%) with good enantioselectivity (up to 83% ee).