Vinylic Organoboranes. 11. A Highly Stereospecific and Regiospecific Synthesis of Trisubstituted Alkenes via Organoboranes

Article abstract of DOI:10.1021/jo00261a005

A highly stereospecific synthesis of trisubstituted alkenes using (E)- and (Z)-2-(1-substituted-1-alkenyl)-1,3,2-dioxaborinanes is presented. (E)-2-(1-Substituted-1-alkenyl)-1,3,2-dioxaborinanes (1), as described previously, readily react with organolithium or Grignard reagents in diethyl ether at -78 deg C to form the corresponding "ate" complexes.Treatment of these "ate" complexes with iodine in methanol induces the migration of the alkyl group from boron to the adjacent carbon, followed by a base-induced deiodoboronation to afford stereodefined trisubstituted alkenes in good yields (50-82percent) and in excellent stereochemical purities (<*>97percent).Similarly (Z)-2-(1-substituted-1-alkenyl)-1,3,2-dioxaborinanes (2), easily obtainable by a previous procedure, react with organolithium or Grignard reagents, followed by treatment with iodine and base, to produce the stereoisomeric trisubstituted alkenes in good yields (65-82percent) and in excellent isomeric purites (<*>97percent).These two procedures provide a convenient route to any of the six possible trisubstituted alkenes, R1CH=CR2R3.