Catalytic preparation of aryl and allylboronic derivatives – BOROCAT

A novel synthetic methodology to access benzylboronic acids and esters has been developed, involving the coupling of the corresponding benzyl halides and pinacolborane (patent FR 2009 and PCT 2010). The main originality of this method is the use of a catalytic amount of metallic Mg as the only catalyst.

The catalytic boration of benzylic halides was made possible by pinacolborane, acting both as the reducing agent and as the borylating agent. The reaction constitutes a “catalytic Grignard-type coupling” and takes place in a single-step under mild conditions, in the absence of noble metals. These results open the perspective of applications to other halide derivatives such as aryl, heteroaryl and allyl halides.

The present project proposes the extension of the catalytic boronic coupling methodology with non expensive metals to the preparation of aryl- and allylboronic derivatives. These compounds are important intermediates, in particular for the Suzuki coupling reaction for the synthesis of non-symmetrical biaryl derivatives, sub-structures frequently met in the fields of pharmacy, crop science, fine chemistry and chemistry of materials.

The combined action of reducing metals such as Mg, Zn, Cu, Fe or Bi with several dialkoxyboranes or other boranes in the presence of additives will be examined in detail in order to define the best conditions for the catalyst recycling and therefore for the catalytic borationmethod.

The access to aryl- and allylboronic acids and esters still remains an unsolved problem from an industrial point of view. The proposed methodology should allow the preparation of the boronic acid derivatives under catalytic and mild conditions, in a environmentally clean process of reduced cost, avoiding both the use of noble metals and of cryogenic conditions.