Synthesis of 4-Isoxazolines via Visible-Light Photoredox-Catalyzed [3 + 2] Cycloaddition of Oxaziridines with Alkynes

Abstract

A method for [3 + 2] cycloaddition of oxaziridines with alkynes to form 4-isoxazolines via visible-light photoredox catalysis is described. This method is a greener, atom-economical reaction that tolerates various functional groups and provides good to excellent yield. Moreover, the cyclization products can be conveniently converted into tetrasubstituted allylic alcohols and enamines. A mechanistic study suggests that the reaction involves photoredox-catalyzed in situ generation of a nitrone from the oxaziridine by SET.

Tandem Reactions of Ynones: via Conjugate Addition of Nitrogen‐, Carbon‐, Oxygen‐, Boron‐, Silicon‐, Phosphorus‐, and Sulfur‐Containing Nucleophiles

“…N ‐Oxides, including quinoline N ‐oxides or isoquinoline N ‐oxides, N ‐methylnitrones and in situ generated N ‐oxides, could be incorporated in the final products. Usually, no metal catalyst was required (Scheme ).…”

“…In 2017, the Woo group developed a visible‐light photoredox‐catalyzed [3+2] cycloaddition for the synthesis of 4‐isoxazolines 104.4 [Eq. (104‐1)].…”

Recent Advances on Metal-Free, Visible-Light- Induced Catalysis for Assembling Nitrogen- and Oxygen-Based Heterocyclic Scaffolds

“…Woo group [75] unveiled that nitrones can be also generated in situ from oxaziridines in photoredox conditions. They described synthetic method for the preparation of 4-isoxazolines 162 in a visible-light photoredox-catalyzed [3 + 2] cycloaddition of oxaziridines 160 with alkynes 161 (Scheme 22a).…”

Recent Advances in the Catalytic Asymmetric Reactions of Oxaziridines

“…Moreover, arynes have also been subjected to the oxaziridine to afford a set of dihydrobenzisoxazoles via the [3+2] cycloaddition [ 96 ]. Recently, the Woo group reported a visible-light photoredox-catalyzed [3+2] cycloaddition of oxaziridines via the C-O bond cleavage [ 97 ]. This methodology was a greener, atom-economical reaction of a set of oxaziridines and alkynes and afforded various 4-isoxazolines in good to excellent yield.…”