Aza‐Büchner–Curtius–Schlotterbeck Reaction Enables Selective Construction of Quaternary Carbon Centers

ABSTRACT Herein, we report the Aza‐Büchner–Curtius–Schlotterbeck reaction (ABCS)– a novel method for the uncatalyzed C─C insertion reaction of photogenerated donor‐donor diazo compounds into aryl aldimines. The transformation proceeds under very mild conditions and high chemoselectivity, favoring C─C over C─H insertion pathways. In a single step, two C(sp 2 )─C(sp 3 ) bonds are formed, granting access to homologated imines bearing a newly constructed quaternary carbon center in good yields. Subsequent hydrolysis gave homologated aldehydes, enabling versatile downstream transformations. The diazo intermediate is generated using a continuous‐flow microreactor, enhancing both safety and scalability. Mechanistic insights, supported by density functional theory (DFT) calculations, reveal the origins of the observed selectivity and reactivity.