Formal Alkenylation and Amination of 2-Nitrobenzofurans with Fumaric Acid Amide Ester under Metal-Free Conditions

An inorganic base promoted metal-free formal alkenylation and amination of 2-nitrobenzofurans is established with fumaric acid amide ester derivatives. The cascade strategy provides the 2-alkenyl and 3-amino substituted benzofurans via Michael addition/cyclization/nitrous acid elimination/N-demethoxylation/C-N bond cleavage and isomerization sequence. The desired 2-(3-aminobenzofuran-2-yl)malonate derivatives are obtained in moderate-to-good yields with high stereoselectivity under mild reaction conditions (up to 71 % yield and >20 : 1 Z : E). The structure of the products is assigned from the single crystal x-ray structural analysis.