Synthesis of Allenes by 1,6‐Addition of Organocuprates to Acceptor‐Substituted Enynes: Scope and Limitations

Acyclic acceptor‐substituted conjugated enynes bearing sulfonyl sulfinyl, sulfonate, nitro, amide, cyano, and oxazolidino groups at the double bond were synthesized and the regioselectivity of their reaction with organocuprates was examined. All Michael acceptors except enynes with nitro and amide functions underwent 1,6‐additions, and the allenyl enolates thus formed were trapped with electrophiles in order to obtain the corresponding allenes. A qualitative reactivity scale for these reactions was established. The dependence of the regioselectivity of both the cuprate addition and the subsequent electrophilic capture on the acceptor group and the substitution pattern of the allenyl enolate were studied. Cyclic 2‐en‐4‐ynoates with endocyclic double bonds were synthesized and treated with organocuprates to afford an exocyclic allene in one case.