Ring Expansion Reactions of Electron-Rich Boron-Containing Heterocycles
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AbstractThe potassium salts of the dianions of isomeric compounds bis-benzocycloborabutylidene, 1, and the ladder diborole 2 were reacted with carbon dioxide (CO2) and carbon monoxide (CO) and the ring expansion products fully characterized. Both dianions 1 and 2 react rapidly with carbon dioxide to form the same insertion product, 3, in which the boron-containing rings are expanded to six-membered rings. Compound 3 is a B–O analogue of binaphtholate. Only dianion 2 reacts cleanly with the weaker electrophile CO, producing a product (4) in which only one of the boron-containing rings is expanded through formal insertion of CO into a B–C bond. The X-ray structures of both 3 and 4 are reported, and reasonable paths to their formation are proposed.
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Organometallics, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/acs.organomet.5b00390.