Dasgupta, AyanPahar, SanjuktaBabaahmadi, RasoolGierlichs, LukasYates, Brian F.Ariafard, AlirezaMelen, Rebecca L.2025-12-162025-12-161615-4150ORCID:/0000-0003-2383-6380/work/198195214https://hdl.handle.net/1885/733795517Decomposition of donor-acceptor diazo compounds leads to the formation of reactive carbene intermediates. These can undergo a wide variety of carbene transfer reactions to yield synthetically useful products. Herein, we report a selective borane catalyzed cyclization reaction from the combination of two different diazo compounds to afford N-substituted pyrazoles. The selective decomposition of the more reactive α-aryl α-diazoester and subsequent reaction with a vinyl diazoacetate produces N-alkylated pyrazoles in a regioselective manner. Catalytic amounts of tris(pentafluorophenyl)borane (10 mol%) were employed to afford the pyrazole products (36 examples) in yields from 59 to 80%. Extensive DFT studies have been undertaken to interpret the mechanism for this reaction which was found to go through two tandem catalytic cycles, both catalyzed by B(C6F5)3. (Figure presented.).AD and RLM would like to acknowledge the EPSRC for an Early Career Fellowship for funding (EP/R026912/1). SP gives thanks to the Newton-Bhabha fellowship for funding. AA, BFY and RB thank the Australian Research Council (ARC) for project funding (DP180100904) and the Australian National Computational Infrastructure Digital Research Services, IT Services at and the University of Tasmania for the generous allocation of computing time. RLM and AA would like to thank Universities Wales for the award of Global Wales International Research Mobility Funding. AD and RLM would like to acknowledge the EPSRC for an Early Career Fellowship for funding (EP/R026912/1). SP gives thanks to the Newton‐Bhabha fellowship for funding. AA, BFY and RB thank the Australian Research Council (ARC) for project funding (DP180100904) and the Australian National Computational Infrastructure Digital Research Services, IT Services at and the University of Tasmania for the generous allocation of computing time. RLM and AA would like to thank Universities Wales for the award of Global Wales International Research Mobility Funding.8enPublisher Copyright: © 2021 The Authors. Advanced Synthesis & Catalysis published by Wiley-VCH GmbHCarbeneDensity Functional TheoryDiazoesterPyrazoleTris(pentafluorophenyl)borane2021-11-2510.1002/adsc.20210131285120827811