GENERAL-METHOD FOR PREPARATION OF ALLENIC ZINC REAGENTS BY 3-CARBON HOMOLOGATION OF TRIORGANOZINCATES - CONVERGENT 3-COMPONENT COUPLING OF PROPARGYLIC SUBSTRATES, TRIORGANOZINCATES, AND ELECTROPHILIC REAGENTS

Allenic zinc reagents (R(1)R(2)C=C=C(R(3))ZnL) are efficiently prepare d by the reaction of propargylic substrates (R(1)R(2)C(X)C=CH, X = MeS O(2)O, Cl, R(2)NCO(2)) with a variety of triorganozincates ((R(3))(3)Z nM; R(3) = alkyl, alkenyl, aryl, M = Li, MgCl). Treatment of the allen ic 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 p ropargylic carbamates (R(1)CH(OCONPh(2))C=CH) with (TMSCH(2))(3)ZnLi a nd 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 r eagents with electrophiles affords functionalized organosilicon compou nds of high synthetic utility.