Organoboranes. 29. A Convenient Synthesis of Alkyldibromoboranes and Dialkylbromoboranes via Hydroboration-Redistribution

Abstract

Trialkylboranes, obtained via hydroboration of terminal and cyclic alkenes with BH3-SMe2, undergo redistribution with boron tribromide at room temperature under the influence of a catalytic amount (7 mol %) of BH3SMe2 in n-pentane to afford the corresponding alkyldibromoboranes or dialkylbromoboranes, depending upon the stoichiometry, thus providing a convenient method for preparing these valuable derivatives. The reaction of trialkylboranes derived from internal alkenes such as tri-3-hexylborane is much slower. However, these derivatives could be transformed into the corresponding alkyldibromoboranes at 70 °C under neat conditions without significant isomerization. The complete conversion of tri-3-hexylborane into di-3-hexylbromoborane could not be achieved. © 1983, American Chemical Society. All rights reserved.