Research Progress in Asymmetric Hydrogenation of Small-Ring Compounds

Given that chiral three-and four-membered cyclic compounds are widely present as key structural units in bioactive molecules and are frequently employed as crucial intermediates in fields such as pharmaceutical development, their synthetic research holds a significant position in the realm of organic chemistry.Transition metal-catalyzed asymmetric hydrogenation reactions (including pressurized hydrogenation and transfer hydrogenation) are ideal methods for constructing chiral small-ring compounds owing to their remarkable catalytic efficiency, excellent enantioselectivity, and scalability.However, various challenges exist and slow down the related development.This review systematically summarizes the latest research progress in the field of asymmetric hydrogenation of small-ring compounds, with a particular focus on studies related to fourmembered ring substrates (such as β-lactams, cyclobutanones, cyclobutenones, and cyclobutenediones) and three-membered ring substrates (including gem-difluorocyclopropenyl esters and gem-difluorocyclopropenyl ketones).