Concise Generation and Diazo-Preserving Diversification of β-Diazoimines

Abstract

Irradiation of a mixture of vinyldiazo esters and azides with blue light, in the absence of any photocatalyst or additive, generates unconventional β-diazoimines. Mechanistically, the reaction involves the selective decomposition of vinyldiazo compounds under blue light to form singlet free vinylcarbenes, which undergo intramolecular [2+1] cyclization to produce unstable cyclopropene-1-carboxylates. These intermediates subsequently participate in a 1,3-dipolar cycloaddition with azides, followed by ring-opening via retro-1,3-dipolar cycloaddition to generate β-diazoimines. One-pot, diazo-preserving diversifications of β-diazoimines provide access to α-diazoesters bearing distal functional groups that are otherwise difficult to introduce. These transformations include nucleophilic addition and reduction to give γ-amino-α-diazoacetates, as well as oxidation to afford β-carboxamido-α-diazoesters. The synthetic potential of these unusual diazo compounds was demonstrated. For example, Rh(II)-catalyzed N–H insertion of γ-amino-α-diazoester afforded azetidine, while reduction of its diazo group with PⁿBu₃ promoted an intramolecular aminolysis to yield a γ-lactam product. Interestingly, controllable intramolecular 1,3-C–H and 1,4-N–H insertion reactions of β-carboxamido-α-diazoester were achieved using different catalyst systems, providing cyclopropane and β-lactam derivatives, respectively.