Silylcuprations allenes

Scheme 3.24. Silylcupration and stannylcupration of allenes under kinetic and thermodynamic control [37c, 67, 95, 96].

See Ref. 28d. The product allenes obtained by treatment of silylcuprates with propargyl subtrates are susceptible to silylcupration. 

Significantly, silylcuprates react with carbamates with syn stereoselectivity59, similar to their reactions with organocuprates62, whereas other nucleofugal groups, such as acetate or methanesulfonate, are displaced in an anti fashion23,27,57. Thus, both enantiomeric (or epimeric) allenes can be obtained from the same propynyl alcohol precursor. 

A route to 3-silylmethyl-l,4-alkadienes involves silylcupration of allenes and trapping of the ensuing organocopper species with allyl phosphate. 

Allenes are obtained from the 1,6-addition to sulfonyl enynes. Actually, acetylene itself is receptive to attack by silylcuprate reagents, giving rise to fZ -alkenylsilanes after trapping with electrophiles. ... 

Silylcupration of Allenes. As a type of activated alkene, allenes undergo silylcupration with reagent (1) to give either vinyl-or allylsilanes. Simple alkylallenes react quickly at —78 °C to give allylsilanes cleanly (eq 7). In this case the silyl group is transferred to the less substituted carbon of the allene. 

Silylcupration of allene with (PhMe2Si)2CuLi followed by treatment of the intermediate cuprate with H" ", carbon electrophiles, and CI2 affords the corresponding vinylsilanes (eq 9). However, reaction of the intermediate cuprate with I2 affords an allylsilane, from which other more highly substituted allylsilanes are readily obtainable (eq 9). In reaction with substituted allenes, the product ratio (vinylsilane vs. allylsilane) is dependent upon the degree of substitution. ... 

Silylcupration of Styrenes and Dienes. Styrene reacts with the silylcuprate (1), but more slowly than with allenes and acetylenes. Nevertheless, the intermediate copper species can be trapped with electrophiles like allyl diphenyl phosphate (eq 16). ... 

C=0 and >C=S bonds. Silylcuprates give allyl and vinylsilanes with allenes... 

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