Alkynylation and Cyanation of Alkenes Using Diverse Properties of a Nitro Group

In the work being reported here, β-nitrostyrenes bearing an ethoxycarbonyl group at the β-position serve as scaffolds for the synthesis of α,β-difunctionalized alkenes. Nitrocinnamates undergo Michael addition reactions with versatile sp3- and sp2-nucleophiles such as alcohols, Grignard reagents, alkylcopper, and dialkylzinc to afford β-substituted nitroethane derivatives. However, various attempts to obtain a double bond via nitrous acid elimination failed because steric repulsion between the newly introduced sp3/sp2 substituent and the nitro group hampered the required anti-coplanar conformation. This problem was successfully overcome using a smaller sp-nucleophile such as lithium acetylide, potassium cyanide, or trimethylsilyl cyanide. While treatment of the adduct with a strong base did not lead to the elimination of nitrous acid, the weaker triethylamine efficiently afforded functionalized enynes and acrylonitriles in high yields.