Boron Conjugate Additions on Electron Deficient Olefins Towards Selective 1,3-Difunctionalization

The presence of carbonyl or imino groups in beta position with regard to the boryl moiety makes them suitable organoboron intermediates for difunctionalized purposes. Catalytic synthetic methodologies have recently been developed to introduce a boryl group at the beta-position of alpha,beta-unsaturated esters, ketones, aldehydes, amides, nitriles, as well as imines and oximes. The asymmetric version favours the chiral C-beta-B formation which can be eventually transformed into useful alcohols or acetyl functional groups. Alternatively, beta-boronate carbonyl or imino compounds can be prepared via alkylation of an enolate with alpha-haloboronates esters. The subsequent route for the preparation of the chiral beta-boronate derivatives required transesterification protocols that successfully provided a series of beta-oximo boronates, beta-imino boronates and beta-carbonyl boronates, with chiral boryl units. This review will enable the reader to understand catalytic and non-catalytic routes for the synthesis of beta-boronate carbonyl and imino compounds. The overall mechanistic insights and the perceptible influence of additives on these different synthetic processes, will be discussed. More emphasis will be placed on further applications of the beta-boronate compounds in the synthesis of diols or aminoalcohols, in particular where beta-chiral centres efficiently control further enantioselective transformation, despite their remote position.