General method for preparation of allenic zinc reagents by three-carbon homologation of triorganozincates: Convergent three-component coupling of propargylic substrates, triorganozincates, and electrophilic reagents

Allenic zinc reagents (R(1)R(2)C=C=C(R(3))ZnL) are efficiently prepared by the reaction of propargylic substrates (R(1)R(2)C(X)C=CH, X = MeSO(2)O, Cl, R(2)NCO(2)) with a variety of triorganozincates ((R(3))(3)ZnM; R(3) = alkyl, alkenyl, aryl, M = Li, MgCl). Treatment of the allenic zinc reagents with D2O gives the corresponding deuteroallenes with high deuterium incorporation. The allenic zinc reagents thus prepared undergo a coupling reaction with a variety of electrophiles (aldehydes, acyl chlorides, I-2, NCS, and chlorosilanes) regioselectively at the gamma position to afford the corresponding propargylic derivatives (R(1)R(2)C(El)C=CR(3), El = RCH(OH), RCO, I, Cl, R(3)Si) in high yields. Silicon containing allenic zinc reagents R(1)CH=C=C(CH(2)SiMe(3))ZnL and R(1)CH=C=C(SiPhMe(2))ZnL are readily prepared by the reaction of propargylic carbamates (R(1)CH(OCONPh(2))C=CH) with (TMSCH(2))(3)ZnLi and by the reaction of bromoproparglic mesylates R(1)CH(OSO(2)Me)C=CBr with (PhMe(2)Si)(3)ZnLi, respectively. Successive treatment of these reagents with electrophiles affords functionalized organosilicon compounds of high synthetic utility.