1,1-Carboboration of Alkynes - Development of an Unusual Reaction

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In our preliminary work we could show that the utilization of strongly Lewis-acidic boranes with pentafluorophenyl substituents enormously enhanced the rates and scope of the 1,1-carboboration reaction. In this situation even die migrating aptitude of hydrogen is sufficient to convert simple terminal alkynes into their respective substituted alkenyl boranes. P-, S- and B-migration takes place under these conditions and one can even carry out 1,1-carboboration reactions of internal alkynes by means of C-C bond activation. These results shall now be used to achieve a substantial expansion of the 1,1 carboboration reaction scheme. We want to prepare extended pi-systems in this way. Subsequent oxidative deborylation will then lead to conjugated enones. Cyclic variants shall be prepared starting from vicinal diacetylenes. We propose the cyclization of unsaturated vicinal diacetylenes to give benzannulated products. One focus of the project will be the development of the chemistry of thiophenes, phospholes and boroles which should become available conveniently by 1,1-carboboration sequences starting from the respective readily prepared doubly acetylide substituted heteroatom containing precursors. Eventually, we have planned to develop simple syntheses to symmetrical and unsymmetrical S-, P- and B-containing cyclic five-membered pi-systems by the 1,1-carboboration scheme, which might potentially be of interest in organic materials science.