L. Meerpoel et al., FACE SELECTIVITY OF THE DIELS-ALDER ADDITIONS AND CHELETROPIC ADDITIONS OF SULFUR-DIOXIDE TO 2-VINYL-7-OXABICYCLO[2.2.1]HEPT-2-ENE DERIVATIVES, Helvetica Chimica Acta, 77(3), 1994, pp. 869-881
Racemic 6-ethenyl-7-oxabicyclo[2.2.l]hept-5-en-2-one (23), 5-ethenyl-7
-oxabicyclo[2.2.1]hept-5-en-2-one (25) and their ethylene acetals 24 a
nd 26, respectively, were derived from the Diels-Alder adduct of furan
to 1-cyanovinyl acetate (27). The Diels-Alder additions of 26 to dime
thyl acetylenedicarboxylate, to methyl propynoate, to N-phenylmaleimid
e, and to methyl acrylate were highly exo-face selective, as were the
cycloadditions of methyl propynoate to dienones 23 and 25 and of dimet
hyl acetylenedicarboxylate to ethylenedioxy-diene 24. The cheletropic
additions of SO2 to 23-26 gave exclusively the corresponding sulfolene
s 57-60 resulting from the exo-face attack of the semicyclic dienes un
der conditions of kinetic and thermodynamic control.