Stereoselective Syntheses of Benz[f]isoindoline‐Derivatives by Intramolecular Cycloadditions of Styrenes to Olefins

Abstract

Abstract The N‐allyl‐N‐cinnamyl amide 10 undergoes thermal cyclization to a 2:1‐mixture of the trans ‐ and cis ‐benz( f )isoindolines 11a and 12a . By comparison, the thermolysis of the corresponding bis‐cinnamylamide 14 proceeds in a highly stereoselective manner to give the cis ‐fused[4+2]‐adduct 16a . Similarly, the trans ‐fused stereoisomeric adducts 30a and 31a were obtained with high stereochemical control on heating the N‐allyl‐N‐diphenylallyl amide 28 . The thermal transformations 4 → 5 + 6a and 17 → 18a + 20a show the competitive formation of [2+2]‐adducts. An alternative approach to (substituted) benz[ f ]isoindolines 16 via the all‐ cis ‐isomer 24a has been developed. The described structures have been assigned on the basis of spectral evidence, chemical correlations and by X‐ray‐diffraction study of the isomer 16b . These results illustrate the utility of substituent interactions in order to direct intramolecular cyclo‐additions at will towards either endo ‐ or exo ‐products.