5-endo cyclizations of NHC-boraallyl radicals bearing ester substituents : characterization of derived 1,2-oxaborole radicals and boralactones
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EPR studies of radical hydrogen abstraction reactions of N-heterocyclic carbene (NHC) complexes of alkenylboranes bearing two ester substituents revealed not the expected boraallyl radicals but instead isomeric 1,2-oaxborole radicals. Such radicals are new, and DFT calculations show that they arise from the initially formed boraallyl radicals by a rapid, exothermic 5-endo cyclization. These spectroscopic and computational discoveries prompted a series of preparative experiments that provided access to a novel family of robust NHC-boralactones. A one-pot procedure was developed to access the boralactones directly from an NHC-borane (NHC-BH3) and dimethyl acetylenedicarboxylate.
Dai , W , McFadden , T R , Curran , D P , Früchtl , H A & Walton , J C 2018 , ' 5- endo cyclizations of NHC-boraallyl radicals bearing ester substituents : characterization of derived 1,2-oxaborole radicals and boralactones ' , Journal of the American Chemical Society , vol. 140 , no. 46 , pp. 15868-15875 . https://doi.org/10.1021/jacs.8b09288
Journal of the American Chemical Society
Copyright © 2018 American Chemical Society. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1021/jacs.8b09288
DescriptionJ.C.W. thanks EaStCHEM for financial support, and D.P.C. thanks the U.S. National Science Foundation. Computational support was provided through the EaStCHEM Research Computing Facility.
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