Intramolecular Cyclization of 3,3-Diarylpropenylamides of Electron-Deficient Alkenes: Stereoselective Synthesis of Functionalized Hexahydrobenzo[f]isoindoles

Intramolecular Diels-Alder reactions of various 3,3-diarylpropenylamides of electron-deficient alkenes to give hexahydrobenzo[f]isoindoles were investigated. Reaction of 1,1,2-ethenetricarboxylic acid 1,1-diethyl ester with 3,3-diaryl-2-propen-1-amines under the amide formation conditions gave the tricyclic compounds in sequential processes involving intramolecular Diels-Alder reaction. The reaction gave cis- and trans-fused tricyclic compounds selectively, depending on the substituents on the benzene ring, reaction temperature and solvent. In the reaction with dissymmetrically substituted 3,3-diaryl-2-propen-1-amines, trans-substituted aryl group reacted mainly as a styrene component. Amides of electron-deficient alkenic carboxylic acids such as fumarate do not undergo cyclization at room temperature sequentially and the reaction on heating gave trans-fused hexahydrobenzo[f]isoindoles. The origin of the observed stereoselectivity has been examined by the DFT calculations.