SYNTHESIS OF THE GRAPEVINE MOTH SEX-PHEROMONE BY GRIGNARD-SCHLOSSER CROSS-COUPLING - THE EFFECT OF THE ELECTROPHILE STRUCTURE ON THE STEREOISOMERIC RATIO IN THE REACTION-PRODUCTS

1-Acetoxy-2E,4Z-heptadiene (4) and 1-bromo-3E,5Z-octadiene (5) were ob tained with greater-than-or-equal-to 90 and 88-92 % configurational pu rity, respectively, starting from 2,4-heptadiyn-1-ol or 3,5-octadiyn-1 -ol. The Li2CuCl4-catalyzed cross-coupling of the allylic acetate 4 wi th 5-tert-butoxypentylmagnesium chloride affords 1-tert-butoxy-7E,9Z-d odecadiene (11) contaminated with greater-than-or-equal-to 25 % of min or stereoisomers in 54-60 % overall yield. Under similar conditions, t he homoallylic bromide 5 reacts with 4-tert-butoxybutylmagnesium chlor ide to give in 50-52 % yield another sample of diene 11 containing les s-than-or-equal-to 17 % of minor stereoisomers. If the latter coupling is carried out with enyne 8 instead of 5 followed by cis-hydrogenatio n of the triple bond in the resulting product, the configurational pur ity of diene 11 is as high as 84.7 % (approximately 45 % overall yield ). The reaction of 11 with Ac2O in the presence of FeCl3 leads directl y to the target 7E,9Z-dodecadienyl acetate (1) with somewhat lower con figurational purity than that of the starting ether 11.