Pheromones via Organoboranes. 2. Vinylic Organoboranes. 8. Applications of the General Stereoselective Synthesis of (E)-Disubstituted Alkenes via Thexylchloroborane-Dimethyl Sulfide to the Synthesis of Pheromones Containing an (E)-Alkene Moiety

Article abstract of DOI:10.1021/jo00376a043

Various (E)-pheromones of the general structure (E)-X-alken-1-yl acetates, (E)-X-alken-1-ols, and (E)-X-alken-1-als have been prepared via thexylchloroborane-dimethyl sulfide (ThxBHCl*SMe2).Hydroboration of acetate-functionalized alkenes with ThxBHCl*SMe2 gives cleanly the corresponding thexylalkylchloroboranes (ThxBRCl, B).Hydridation of B with potassium triisopropoxyhydride (KIPBH) at -78 deg C gives cleanly the corresponding thexylalkylboranes (ThxBRH, C).These are quenched immediately with 1-halo-1-alkynes to give B-(cis-1-halo-1-alkenyl)thexylalkylboranes (D).Treatment of D with sodium methoxide results in the displacement of bromine by the alkyl group on boron to produce B-(trans-1-alkyl-1-alkenyl)thexylborinates (E).Protonolysis of E with acetic acid provides (E)-X-alken-1-yl acetates in high yields and in >99percent isomeric purities.Treatment of (E)-X-alken-1-yl acetates with base affords the corresponding (E)-X-alken-1-ols.Oxidation of (E)-X-alken-1-ols with dimethyl sulfoxide activated by oxalyl chloride or the complex of dimethyl sulfide and chlorine produces (E)-X-alken-1-als quantitatively.By properly choosing the starting functionalized alkenes and 1-halo-1-alkynes, various (E)-pheromones can be prepared easily.The present procedure appears to be general.There does not appear to be any limitation on the length of the carbon chain or the position of the double bond in the target molecules.