Pyrolysis of tricyclic cyclobutane-fused sulfolanes as a route to cis-1,2-divinyl compounds and their Cope-derived products

Abstract

Functionalisation of the double bond of 3-thiabicyclo[3.2.0]hept-6-ene 3, readily formed by hydrolysis of the [2+2] cycloadduct 1 of 3-sulfolene and maleic anhydride followed by oxidative bis-decarboxylation, gives tricyclic sulfones 5–7 and 9 with the bicyclo[3.3.0.0^2,4] skeleton. FVP of 3 results in stereospecific extrusion of SO₂ to give Z-hexa-1,3,5-triene which undergoes electrocylisation to give cyclohexa-1,3-diene while reaction of 3 with LiAlH₄ results in non-stereospecific extrusion to give Z- and E-hexa-1,3,5-triene. Upon FVP the tricyclic sulfones 5–7 and 9 lose SO₂ to give 7-membered ring products 16–19 by Cope rearrangement of the initially formed cis-1,2-divinyl intermediates 15. The 1,3-dipolar cycloaddition of nitrile oxides and a nitrone to the double bond of 3 gives tricyclic sulfones with the tricyclo[5.3.0.0^2,6] skeleton and a wider variety of these can be prepared by conventional reactions of 1. Upon FVP these lose SO₂ to give stable cis-1,2-divinyl compounds 23, 24, 37–40 and 41–44. The Diels–Alder adducts 48 and 49 have been prepared from 3 and these behave differently upon FVP, losing SO₂ and butadiene to give tetrasubstituted benzenes, in the latter case by way of an unexpected tetracyclic intermediate.