Electrophilic reactions of α-amino dienenitriles: regiochemistry and stereoselectivity of trisubstituted pentadienyl anions

Abstract

A pentadienyl anion 7a generated from 2-N-methylanilinohepta-3,5-dienenitrile reacted at the γ-site with halogenoalkanes to give predominantly the products 9γ–2γ having the 2Z,5E-configuration, while it reacted at the ε-site with conjugated aldehydes to give mainly the products 27ε–29ε having the 2Z,4E-configuration. An intermediate of the pentadienyl ion 7a having a lithium atom σ-bonded to the γ-carbon and chelated with the anilino group was proposed to account for the regio- and stereo-selectivities observed in the above reactions. The alkylation reactions in the presence of a dipolar co-solvent HMPA tended to enhance the 2Z-selectivity. The pentadienyl anions derived from the α-anilino dienenitriles 30–33 having different ε-substituents such as phenyl, phenylthio, benzyloxy and ethoxycarbonyl groups also reacted with halides and aldehydes both regio- and stereo-selectively.