Cyanocuprates, reactions with enynes

Additional routes to a-allenic-a-amino acids were described more recently and utilize radical [136] or transition metal-catalyzed [137] allenylations, in addition to copper-promoted Michael additions [15b]. Thus, sterically demanding amino acid derivatives (e.g. 151) are accessible via a 1,6-addition reaction of lithium di-tert-butyl-cyanocuprate with acceptor-substituted enynes of type 150 (Scheme 18.48). 

So-called lower order cyanocuprates RCu(CN)Li do not generally react with acceptor-substituted enynes. An exception is the cuprate t-BuCu(CN)Li which undergoes anti-Michael additions with 2-cn-4-ynoates and nitriles (equation 61)151. The mechanistic aspects of this very unusual reaction are unknown radical intermediates and electron transfer steps have not been found. 

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