Investigations on peri-, regio- and stereoselectivities in thermal cycloadditions involving C-(4-oxo-4H[1]benzopyran-3-yl)-N-phenylnitrones:: Role of steric factors and secondary interactions in 1,3-dipolar cycloadditions

Complete peri-, regio- and stereoselectivities in thermal reactions of C-(4-oxo-4H[1]benzopyran-3-yl)-N-phenylnitrones with both electron-rich and electron-deficient olefins have been investigated. This conjugated nitrone undergoes frontier-orbital (LUMO-dipole HOMO-dipolarophile) controlled exo-selecitve 1,3-dipolar cycloadditions; the stereo-chemical outcome is influenced predominantly by steric factors, besides secondary orbital and/or polar interactions. (C) 2000 Elsevier Science Ltd. All rights reserved.