Haloboration of o‐Alkynyl Phenols Generates Halogenated Bicyclic‐Boronates**

Abstract

Benzoxaborinines are intermediates en‐route to bicyclic boronates that are important active pharmaceutical ingredients (APIs). Herein, the haloboration of o‐alkynyl‐phenols using BX3 (X=Cl or Br) is disclosed as a route to form C4‐X‐benzoxaborinines with good functional group tolerance. Computational studies indicated that there are two similar in barrier mechanisms: (i) double alkyne haloboration followed by retro‐haloboration; (ii) concerted trans‐haloboration involving an exogenous chloride source. The C4‐halide in these benzoxaborinines is useful, with a one‐pot haloboration‐Negishi cross coupling protocol effective to form benzoxaborinines with an alkyl or an aryl at C4. Therefore this method is a useful addition to the toolbox for synthesising bicyclic‐boronates that are attracting increasing attention as APIs.