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α-Selective Ring-Opening Reactions of Bicyclo[1.1.0]butyl Boronic Ester with Nucleophiles
Lin Guo1, Adam Noble1, Varinder K Aggarwal1
1Bristol University, Department of Chemistry, Cantock's Close, Bristol, BS8 1TS, UK.
Abstract:
The reaction of bicyclo[1.1.0]butyl pinacol boronic ester (BCB-Bpin) with nucleophiles has been studied. Unlike BCBs bearing electron-withdrawing groups, which react with nucleophiles at the β-position, BCB-Bpin reacts with a diverse set of heteroatom (O, S, N)-centred nucleophiles exclusively at the α-position. Aliphatic alcohols, phenols, carboxylic acids, thiols and sulfonamides were found to be competent nucleophiles, providing ready access to α-heteroatom-substituted cyclobutyl boronic esters. In contrast, sterically hindered bis-sulfonamides and related nucleophiles reacted with BCB-Bpin at the β'-position leading to cyclopropanes with high trans-selectivity. The origin of selectivity is discussed.
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