Allenic zinc reagents (R1R2CCC(R3)ZnL) are efficiently prepared by the reaction of propargylic substrates (R1R2C(X)C⋮CH, X = MeSO2O, Cl, R2NCO2) with a variety of triorganozincates ((R3)3ZnM; R3 = 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, I2, NCS, and chlorosilanes) regioselectively at the γ position to afford the corresponding propargylic derivatives (R1R2C(El)C⋮CR3, El = RCH(OH), RCO, I, Cl, R3Si) in high yields. Silicon containing allenic zinc reagents R1CHCC(CH2SiMe3)ZnL and R1CHCC(SiPhMe2)ZnL are readily prepared by the reaction of propargylic carbamates (R1CH(OCONPh2)C⋮CH) with (TMSCH2)3ZnLi and by the reaction of bromoproparglic mesylates R1CH(OSO2Me)C⋮CBr with (PhMe2Si)3ZnLi, respectively. Successive treatment of these reagents with electrophiles affords functionalized organosilicon compounds of high synthetic utility.

Treatment of terminal alkynes bearing a remote leaving group with MNR(2) (M = Li, Na, K) gives bicyclo[n.3.0]-1-alkenes (n = 3, 4). The tandem cyclization proceeds through a mechanism involving exo-cyclization of an alkynylmetal intermediate and intramolecular C-H insertion of the resulting carbenoid.

The reaction of 5-hexynyl tosylate (3a) with alkynyllithium (RC⋮CLi; R = Ph, TMS) gives enynes 5 and 6. The reaction proceeds through a mechanism involving a novel exo-type cyclization of 6-lithio-5-hexynyl tosylate to form cyclopentylidene carbene. Enyne 6 is produced by the addition of RC⋮CLi to the carbene, whereas rearrangement of the carbene to cyclohexyne followed by carbolithiation with RC⋮CLi gives enyne 5. The formation of cyclopentylidene carbene and cyclohexyne as intermediates is clearly demonstrated by trapping experiments with cyclohexene (and triethylsilane) and with 1,3-diphenylisobenzofuran, respectively. Alkynyllithiums derived from 3-butynyl and 6-heptynyl p-fluorobenzenesulfonates (19a,b) undergo a similar exo-type cyclization to give cyclopropylidene and cyclohexylidene carbenes, respectively.

reactions of organo-metal compounds reactions of organo-metal compounds O 0350 -062General 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 are prepared by reaction of propargylic substrates with a variety of triorganozincates. They undergo a subsequent coupling reaction with a variety of electrophiles (e.g. aldehydes) regioselectively at the γ-position to afford the corresponding propargylic derivatives. This is a general method for the three-carbon homologation reaction giving anti-homopropargylic alcohols. By using silicon-containing allenic zinc reagents, this method provides functionalized organosilicon compounds of high synthetic utility.-(HARADA, T.; KATSUHIRA, T.; OSADA, A.; IWAZAKI, K.; MAEJIMA, K.; OKU, A.; J.

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