A. Hassner et al., CINE SUBSTITUTION IN 2-OXABICYCLO[4.2.0]OCTANONES AND SUBSEQUENT UNUSUAL REARRANGEMENTS, Journal of organic chemistry, 61(12), 1996, pp. 4051-4058
Reaction of 2-chlorooxabicyclo[4.2.0]octanone 5 with several nucleophi
les was examined and found to differ significantly from those of carbo
n analog 1. MeO(-) and PhS(-) led either to products of cine substitut
ion 9 or of ring opening to cyclobutenones 8. With most enolates cine
substitution occured via C-alkylation of the intermediate oxidoallyl c
ation in spite of formation of a new C-C bond between two quaternary c
arbons; with nitroalkanes O-alkylation was preferred. With azide as a
nucleophile, further transformations occurred, among them an oxy-promo
ted electrocyclic cyclobutane opening, with incorporation of a phenyl
triazole unit and final formation of the unusual product 19a. Evidence
for a mechanism explaining formation of 19a was obtained by isolation
of intermediates. Thermolysis or photolysis of Se or 9b led via elect
rocyclic ring opening to a vinyl ketene which was trapped by MeOH, alk
enes, dienes, or oxygen to produce polyfunctional unsaturated esters 2
9 and 30 or 8-membered ring lactone 31, fused cyclobutanones 33 and 34
, pyranone 38, or gamma-lactone 39, respectively.