1,2-Thiazines and related heterocycles. Part 3. The mechanism and regioselectivity of the cycloadditions of N-sulphinylamino compounds with dienes

Abstract

A kinetic investigation indicates the mechanism of reaction of ethyl N-sulphinylcarbamate with 1,1′-bicyclohexenyl to be pericyclic. It is argued that N-sulphinylamino compounds, in general, cycloadd to dienes by a similar mechanism. Contradictions in the literature concerning the regioselectivity shown in the reactions of N-sulphinylamino compounds with unsymmetrical dienes are resolved. The suitability of Hückel frontier orbitals in accounting for observed regioselectivities is investigated. For the systems studied it is possible to define regioselectivity ratios for the reactions which are independent of the nature of the transition state. A consideration of the regioselectivity ratios given by various parameterisations of the NSO group, together with the probable nature of the transition state, shows that the regioselective behaviour of sulphinylamino compounds is comprehensible in the frontier orbital approximation.