Construction of Chiral Cyclic Compounds Enabled by Enantioselective Photocatalysis

Abstract

Chiral cyclic molecules are some of the most important compounds in nature, and are widely used in the fields of drugs, materials, synthesis, etc. Enantioselective photocatalysis has become a powerful tool for organic synthesis of chiral cyclic molecules. Herein, this review summarized the research progress in the synthesis of chiral cyclic compounds by photocatalytic cycloaddition reaction in the past 5 years, and expounded the reaction conditions, characters, and corresponding proposed mechanism, hoping to guide and promote the development of this field.

Roles of Nonadiabatic Processes, Reaction Mechanism, and Selectivity in Cu-Catalyzed [2 + 2] Photocycloaddition of Norbornene and Acetone to Oxetane

“…The [2 + 2] photocycloaddition reaction is a typical photochemical reaction for the formation of four-membered rings, which can occur either by direct excitation of substrates or through photocatalysts. − One of the most famous photocycloadditions is the Paternò-Büchi reaction, which involves carbonyl derivatives and alkenes to form oxetanes (Scheme a). − This reaction is activated by direct excitation of carbonyl derivatives and subsequent CC double bond engagement . Li et al advanced this photocycloaddition by direct excitation of noncovalent complexes comprising alkene and carbonyl substrates under visible-light irradiation, providing fresh insights into the extensively studied Paternò-Büchi reaction (Scheme b) .…”

“…However, these photocycloaddition reactions without photocatalysts are generally limited by the direct excitation of specific substrates. For the general synthesis of oxetanes via the Paternò-Büchi reaction, a good option is using photocatalysts, among which organometallic complexes are excellent candidates because of their strong light absorption, excellent chemical stability, and long triplet-state lifetime. ,,,,− Becker et al reported a visible-light-driven intramolecular aza Paternò-Büchi reaction to produce azetidines from imines and alkenes using an Ir photocatalyst (Scheme c) . The selective activation of the alkene moiety is triggered by energy transfer from the Ir complex.…”