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

The selective introduction of a boron unit in an organic framework opens new perspectives in both building block design and functionalization protocols. The presence of carbonyl or imino groups in β 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 β- position of α,β-unsaturated esters, ketones, aldehydes, amides, nitriles, as well as imines and oximes. The asymmetric version favours the chiral Cβ-B formation which can be eventually transformed into useful alcohols or acetyl functional groups. Alternatively, β-boronate carbonyl or imino compounds can be prepared via alkylation of an enolate with α-haloboronates esters. The subsequent route for the preparation of the chiral β-boronate derivatives required transesterification protocols that successfully provided a series of β-oximo boronates, β-imino boronates and β-carbonyl boronates, with chiral boryl units. This review will enable the reader to understand catalytic and non-catalytic routes for the synthesis of β-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 β-boronate compounds in the synthesis of diols or aminoalcohols, in particular where β-chiral centres efficiently control further enantioselective transformation, despite their remote position.