Pheromones Via Organoboranes. 3. Vinylic Organoboranes. 10. Stereospecific Synthesis of (Z)- and (E)-6- and -7-Alken-1-Ols Via Boracyclanes

Abstract

Treatment of B-(E)-1-alkenylborinanes, obtained via monohydroboration of 1-alkynes with borinane, with iodine in the presence of a base results in the migration of one end of the cycloalkyl chain from boron to the adjacent carbon, producing intermediates containing the seven-membered borepane moiety, which undergo rapid deiodoboronation to afford the (Z)-6-alkenyl-1-boronate esters. These boronate esters, upon oxidation, provide (Z)-6-alken-1-ols. The procedure is successfully extended to B-(E)-1-alkenylborepane derivatives to produce (Z)-7-alken-1-ols. The preparation of (E)-6- and -7-alken-1-ols has been carried out via borinane and borepane derivatives. Borinane, as prepared previously, hydroborates cleanly 1-bromo-1-alkynes to provide the B-((Z)-1-bromo-1-alkenyl)borinanes. Treatment of these boron intermediates with sodium methoxide results in the displacement of bromine by one end of the boracycloalkyl moiety, producing the corresponding vinylboranes containing the seven-membered borepane moiety. The intermediates, upon controlled protonolysis, followed by oxidation, afford the (E)-6-alken-1-ols. The methodology was extended to borepane derivatives to provide (E)-7-alken-1-ols. The above procedures constitute a simple, very convenient, stereospecific, and general one-pot synthesis of (Z)- and (E)-6- and -7-alken-1-ols. The methodology has been applied to the synthesis of representative pheromones containing a (Z)- or an (E)-alkene moiety in good yields. © 1988, American Chemical Society. All rights reserved.