Asymmetric hydrogenation and transfer hydrogenation in the enantioselective synthesis of flavonoids

Abstract

Asymmetric hydrogenation (AH) and asymmetric transfer hydrogenation (ATH) are versatile synthetic methodologies widely employed in the preparation of chiral compounds. In this review, we explore the applications of AH and ATH in the total synthesis of natural flavonoids and their analogues, highlighting the limitations and opportunities in the field. Regarding AH, the hydrogenation of the CC bond of chromenes and cinnamic acid derivatives leads to isoflavans, flavans, flavanones and homoisoflavones with excellent enantioselectivity. Analogously, the ATH of CO and CC/CO bonds results in enantioenriched alcohols, which upon oxidation, deoxygenation or cyclization allow the synthesis of a myriad of flavonoids, isoflavonoids and homoisoflavonoids with excellent yields and ee values.