H~LLAR AUKS~ and PETER YATES. Can. J. Chem. 59,2510.6-Acetoxy-2,6-dimethyl-2,4-cyclohexadienone (1) and maleic anhydride in boiling benzene give a single adduct, exo-5-acetoxy-1,5-dimethyl-6-oxobicyclo[2.2.2]oct-7-ene-endo-2,3-dicboxylic acid anhydride (2). With propiolic acid 1 gives exo-5-hydroxy-1,5-dimethyl-6-oxobicyclo[2.2.2]octa-2,7-diene-2-carboxylic acid (15). The high stereoselectivity and regioselectivity of these reactions is interpretable in terms of orbital overlap, closed-shell repulsion, steric, and van der Waals -London effects.-

"Modified" Wessely oxidation of 2,6-dimethylphenol with lead tetraacetate in the presence of acrylic acid, cinnamic acid, cis-β-bromoacrylic acid, trans-β-bromoacrylic acid, methyl hydrogen maleate, methyl hydrogen fumarate, and tiglic acid followed by intramolecular cycloaddition gives exo-6-hydroxy-4,6-dimethyl-5-oxobicyclo [2.2.2]oct-7-ene-exo-2-carboxylic acid lactones. Analogous products have been obtained from o-cresol. Structural assignments have been made on the basis ofthe ir, uv, and 1H nmr spectra of the products; analysis of the last shows that the geometry of the bicyclo[2.2.2]octenone system is distorted by the presence of the lactone ring. Chemical transformations of two of the products from the "modified" Wessely oxidation–intramolecular cycloaddition sequence have demonstrated that this route may be used to prepare regioisomers or stereoisomers of products obtained by the conventional Wessely oxidation–intermolecular cycloaddition sequence.

A number of sulfoxides derived from 3-benzylthiopropionic acid, S-benzylcysteine, and S-phenylcystelne have been synthesized and exposed to typical Pummerer reaction conditions. Cyclization of the S-benzyl sulfoxides to six-membered or seven-membered heterocyclic rings (1,3-thiazin-4-ones and 1,3,6-oxathiazepines) is observed only in acetic anhydride solvent and only after conversion of the carboxyl group to an amide or peptide. Cyclization of S-phenylcysteinyl amides to β-lactams could not be achieved. The thiazolidine isomers of the six- and seven-membered rings have been synthesized and found not to be intermediates in the acetic anhydride reactions. The thiazolidines do rearrange to the six- and (or) seven-membered rings in anhydrous trifluoroacetic acid solvent. S-Benzylphthalimidocysteinylglycine sulfoxide, a 3:2 mixture of epimers at sulfur, affords a 3:2 mixture of isomeric thiazinones. A mechanism for these cyclizations is proposed, and it is suggested that the configuration at sulfur controls the configuration at the new asymmetric centre in the product.

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