REACTIONS OF 1,1-DIHALOALKENES WITH TRIORGANOZINCATES - A NOVEL METHOD FOR THE PREPARATION OF ALKENYLZINC SPECIES ASSOCIATED WITH CARBON-CARBON BOND FORMATION

Lithium trialkylzincates react with 1,1-dibromoalkenes 1 and 1-bromo-1-chloroalkenes 2 at -85-degrees-C in THF to give 1-bromoalkenes 5 and 1-chloroalkenes 7, respectively, upon hydrolysis. The intermediate (1-haloalkenyl)zincates 4 and 6 are stable at low temperature but, when allowed to warm to 0-degrees-C, they undergo a 1,2-alkyl migration reaction to afford alkenylzinc species 10. A variety of alkylation products 11 are obtained by the hydrolysis of 10. In the presence of (Ph3P)2Pd (5 mol%), alkenylzinc species 10 react smoothly with organic halides (AcCl, EtOCOCl, CH2=CH-(Me)Br, PhBr) to yield the corresponding coupling products 13-16.