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Mechanistic Insights Into the B(C6F5)3-catalyzed Wolff Rearrangement/[2 + 2] and [4 + 2] Cascade Cyclization of
Haili Wen1, Yanshu Luo1, Yuanzhi Xia1
1College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, 325035, China.
Abstract:
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.
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