Reactions of β-nitro-substituted 1<i>H</i>-benzo[<i>f</i>]chromenes and benzofurans with nucleophiles

Abstract

A series of 3-alkoxy-2-nitro-2,3-dihydro-1 H -benzo[ f ]chromenes as a mixture of cis - and trans -isomers was obtained in the reaction of 2-nitro-1 H -benzo[ f ]chromenes with alcohols. The reaction with secondary cyclic amines and 3-amino-5,5-dimethylcyclohex-2-en-1-one proceeds trans -diastereoselectively to form Michael adducts of benzochromane structure. Conjugated addition involving anilines leads to (2-hydroxy-1-naphthyl) methyl-substituted β-nitroenamines. The nucleophilic dearomatization of 3-nitrobenzofurans under the action of primary aromatic amines was shown to involve sequential aza- and retro-oxa-Michael reactions. This reaction illustrates the high propensity of 3-nitrobenzofurans to open the furan cycle.