Mechanistic Insights Into the B(C ₆ F ₅ ) ₃ ‐catalyzed Wolff Rearrangement/[2 + 2] and [4 + 2] Cascade Cyclization of α‐Diazoketones With Imines

Presented herein is a DFT investigation of the B(C₆F₅)₃-catalyzed system involving the Wolff rearrangement/[2 + 2] and [4 + 2] cascade cyclization of α-diazoketones with imines. The study provides a detailed elucidation of ketene formation through B(C₆F₅)₃-promoted Wolff rearrangement of α-diazoketones, alongside the substrate-dependent chemoselectivity observed in cyclization with imines. The investigation reveals a three-step Wolff rearrangement process, involving B-O adduct formation, carbene species generation via N₂ extrusion and facile 1,2-migration. Computational studies successfully replicate the substrate-dependent chemoselectivity observed experimentally in the cyclization of the resulting ketene intermediate with different N-protected imines. Notably, N-tert-butoxycarbonyl imines exhibit preferential stepwise [2 + 2] cyclization, while N-tert-butylcarbonyl imines favor concerted [4 + 2] cycloaddition. The divergence in these reactions is rationalized through distortion/interaction analysis of critical transition states.