1,2-Thiazines and related heterocycles. Part 4. The mechanism and periselectivity of the cycloadditions of N-sulphinylaminoazines with 1,4-epoxy-1,4-dihydronaphthalenes

Abstract

A kinetic investigation indicates that the cycloadditions of various N-sulphinylaminoazines, reacting as heterodienes, to 1,4-epoxy-1,4-dihydronaphthalene and its bridgehead methylated derivatives are pericyclic. The cycloadditions of the unsymmetrical 2- and 3-(N-sulphinylamino)pyridines are strongly periselective giving only the peri-isomers coupled via sulphur and ring positions 1 and 2, respectively. This selectivity can be accounted for in terms of Hückel orbitals if all π-interactions are considered; the frontier orbital approximation fails on account of the close spacing of orbital energies that occurs in extensively conjugated compounds.