Synthesis of chiral allyl and propargyl boronates by organocatalytic carbene insertion to carbon-boron bonds

Abstract: This thesis describes the development of a novel organocatalytic method for the synthesis of chiral allyl- and propargyl- organoboron compounds with high enantioselectivity. These organoboron species are versatile building blocks in asymmetric synthesis.We have developed a new efficient homologation method of alkenyl boronic acids. This reaction affords enantiomerically enriched trifluoromethylated allylboronates. These organoboron species were used in allylboration of carbonyl compounds, imines and indole derivatives. The reactions proceeded with a remarkably high stereoselectivity to give homoallylic alcohols and amines. In addition, the chiral allylboronic acids can be oxidized to the corresponding alcohols with retention of the configuration.Based on the homologation of alkenylboronic acids a new three-component reaction is developed. This reaction involved coupling of alkynyl boronates, diazo compounds and ketones in the presence of chiral organocatalysts. This coupling proceeds with high selectivity under mild reaction conditions. The three-component coupling reaction is based on a homologation–allylboration sequence. The process is suitable for synthesis of CF3- and TMS-substituted allenols with excellent diastereo- and enantioselectivity. Application of aromatic, cyclic and non-cyclic ketones leads to formation of chiral tertiary allenols.We have also studied the effects of boronic acid esters on the outcome of the homologation reaction. It was found that a facile transesterification of the boronate precursors with the organocatalyst, BINOL derivatives, is a prerequisite of the successful homologation reaction.