Haloboration and Its Application to Organic Synthesis

Abstract

Although the haloboration reaction would be considered to provide useful application to organic synthesis, the reaction has not adequately developed for such purposes. Most recently, we found that B-halo-9-borabicyclo [3,3,1] nonane (B-X-9-BBN, X = Br or I) reacts with 1-alkynes stereo-, regio-, and chemoselectively. For example, the bromoboration of 1-alkynes with B-Br-9-BBN is very facile and complete within a few hours via a cis addition of the Br-B bond to the terminal triple bond. Such a reaction was confirmed to occur only at terminal triple bonds, but not at internal triple bonds, terminal and internal double bonds. The sequential treatments of the haloboration products afford convenient methodologies of obtaining 2-halo-1-alkenes, (Z)-l-alkynyl-2-halo-1-alkenes, (E) and (Z)-l,2-dihalo-1-alkenes, (Z)-δ-halo-γ,δ-unsaturated ketones, α-bromoaldehydes, 1,1-dialkylethenes, 1-halo-2, 2-dialkylethenes, trisubstituted ethenes and others. © 1985, The Society of Synthetic Organic Chemistry, Japan. All rights reserved.