Organocopper compounds, reactions with dienes

As in the case of addition reactions of carbon nucleophiles to activated dienes (Section HA), organocopper compounds are the reagents of choice for regio- and stereoselective Michael additions to acceptor-substituted enynes. Substrates bearing an acceptor-substituted triple bond besides one or more conjugated double bonds react with organocuprates under 1,4-addition exclusively (equation 51)138-140 1,6-addition reactions which would provide allenes after electrophilic capture were not observed (cf. Section IV). 

Whereas these and other reports did not indicate the possibility of 1,4-cuprate additions to activated dienes, Yamamoto and co workers" showed in their seminal contributions that this is indeed feasible while the reaction of methyl sorbate with the Gilman cuprate M-Bu2CuLi provided exclusively the 1,6-addition product, the reagent formed from butylcopper and the Lewis acid boron trifluoride led to the 1.4-adduct as the major product (equation 15). The synthetically veiy useful organocopper compounds RCu have been named Yamamoto reagents. In certain cases, the regioselectiv-... 

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