Vinylic Organoboranes. 12. Synthesis of (Z)-1-Halo-1-alkenes via Hydroboration of 1-Halo-1-alkynes Followed by Protonolysis

Article abstract of DOI:10.1021/jo00287a017

Practical conditions have been developed for synthesizing (Z)-1-halo-1-alkenes from 1-halo-1-alkynes.The reaction of 1-halo-1-alkynes with dicyclohexylborane (Chx2BH) or with 9-borabicyclo<3.3.1>nonane (9-BBN) gives exclusively the corresponding B-((Z)-1-halo-1-alkenyl)dialkylboranes 1.No dihydroboration products were found.A general procedure is reported for protonolyzing 1 with AcOH, yielding the (Z)-1-halo-1-alkenes.The synthesis of these haloalkenes is particularly convenient using Chx2BH in pentane.In this solvent, the synthesis of Chx2BH, the subsequent hydroboration and protonolysis, and the removal of the borane residue with ethanolamine all go smoothly and rapidly with nearly quantitative yields.