Unveiling the role of boroxines in metal-free carbon-carbon homologations using diazo compounds and boronic acidsElectronic supplementary information (ESI) available. See DOI: 10.1039/c7sc02264f, additional data is available from the University of Cambridge Data Repository Website: https://doi.org/10.17863/CAM.10823

By means of computational and experimental mechanistic studies the fundamental role of boroxines in the reaction between diazo compounds and boronic acids was elucidated. Consequently, a selective metal-free carbon-carbon homologation of aryl and vinyl boroxines using TMSCHN 2 , giving access to TMS-pinacol boronic ester products, was developed. By means of computational and experimental mechanistic studies the fundamental role of boroxines in the reaction between diazo compounds and boronic acids was elucidated.