Anionic Halocuprate(II) Complexes as Catalysts for the Oxaziridine-Mediated Aminohydroxylation of Olefins

Abstract

We have discovered that the oxaziridine-mediated copper-catalyzed aminohydroxylation reaction recently discovered in our labs is dramatically accelerated in the presence of halide additives. The use of this more active catalyst system enables the efficient aminohydroxylation of electronically and sterically deactivated styrenes, and also enables the use of non-stereogenic 3,3-dialkyl oxaziridines as terminal oxidants in the aminohydroxylation reaction. We present evidence that anionic halocuprate(II) complexes are the catalytically active species responsible for the increased reactivity under these conditions. This unexpected observation has led us to re-evaluate our mechanistic understanding of this reaction. Based upon the results of a variety of radical trapping experiments, we propose a modified mechanism that involves a homolytic reaction of the olefin with a copper(II)-activated oxaziridine. Together, the observation that anionic additives significantly increase the oxidizing ability of oxaziridines and the recognition of the radical nature of reactions of oxaziridines under these conditions suggest that a variety of new oxidative transformations catalyzed by halocuprate(II) complexes should be possible.

Recent Developments in Methodology for the Direct Oxyamination of Olefins

“…Both the regio-and chemoselectivity of this reaction can be rationalised by the Cu II /Cu III catalytic cycle proposed by the authors (Scheme 30). [52] The first step of the reaction is the homolytic addition of the alkene 75 to the metallo-oxaziridine 74, to generate the most stabilised carbon radical 76. Intramolecular radical-radical recombination then regenerates the catalyst and furnishes the oxyaminated product 77.…”

“…Anionic halocuprate complexes [CuA C H T U N G T R E N N U N G (F 6 acac) 2 ] were found to be highly active catalysts for this transformation, [52] as they are capable of oxyaminating electron-deficient styrenes with significantly higher yields and shorter reaction times.…”

Five-membered oxaza heterocyclic compounds on the basis of epoxides and aziridines

“…One-pot processes were treated as [4 + 3]-interaction of ambiphilic reagents where opening of the oxirane ring is followed by S N Ar reaction or oxa-Michael cyclization (Scheme 121). Benkovics et al [238] described a procedure for the synthesis of oxazolidines from oxaziridines 215 in the presence of anionic halocuprate(II) complexes (Scheme 122). The authors proposed two possible mechanisms for the reactions of oxaziridines with alkene substrates, two-step electrophilic (path a) and homolytic (path b; Scheme 123).…”

Synthesis of 2-Aryl- and 2-Vinylpyrrolidines via Copper-Catalyzed Coupling of Styrenes and Dienes with Potassium β-Aminoethyl Trifluoroborates

“…While pyrrolidine formation without ring-opening is feasible, it is also possible the ring could open and subsequently close prior to pyrrolidine formation. 44 …”