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.