Visible-Light-Driven Strain-Increase Ring Contraction Allows the Synthesis of Cyclobutyl Boronic Esters |
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Authors: | Dr Raffael Davenport Dr Mattia Silvi Dr Adam Noble Dr Zied Hosni Dr Natalie Fey Prof Dr Varinder K Aggarwal |
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Institution: | School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS UK |
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Abstract: | There are a limited number of ring-contraction methodologies which convert readily available five-membered rings into strained four-membered rings. Here we report a photo-induced radical-mediated ring contraction of five-membered-ring alkenyl boronate complexes into cyclobutanes. The process involves the addition of an electrophilic radical to the electron-rich alkenyl boronate complex, leading to an α-boryl radical. Upon one-electron oxidation, ring-contractive 1,2-metalate rearrangement occurs to give a cyclobutyl boronic ester. A range of radical precursors and vinyl boronates can be employed, and chiral cyclobutanes can be accessed with high levels of stereocontrol. The process was extended to the preparation of benzofused cyclobutenes and the versatility of the boronic ester was demonstrated by conversion to other functional groups. |
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Keywords: | Borchemie Cyclobutane Metallatumlagerungen Photoredoxkatalyse Ringkontraktion |
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