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 D 2 O 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 γ 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.