Carbonyl Imines from Oxaziridines: Generation and Cycloaddition of NOC Dipoles

Abstract

Cycloaddition reactions of nitrones,i azides,ii and related 1,3-dipolar species iii have become recognized as powerful tools for the construction of compounds with great utility in organic synthesis, chemical biology, and materials science. The conceptual model that underpins our understanding of this broad class of reactions was first formalized by Huisgen in 1963. iv This seminal contribution to organic chemistry provided chemists with a unified framework for understanding the structure and reactivity of 1,3-dipolar compounds, and also predicted the structures of several elementary 1,3-dipoles that were unknown at the time. Subsequent research has identified cycloaddition reactions of many of these predicted 1,3-dipolar species.v However, carbonyl imines (e.g., 3, Scheme 1) have remained elusive in the half-century since Huisgen’s initial prediction. Although these unusual dipoles have been postulated to be intermediates in the photochemical decomposition of nitroarenes,vi no compounds resulting from dipolar cycloadditions of carbonyl imines have previously been reported. In this communication, we demonstrate that carbonyl imines can be efficiently generated by Lewis acid-catalyzed rearrangement of N-sulfonyl oxaziridines and trapped by cycloaddition with a variety of dipolarophiles.