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 P n Bu₃ 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.