1.3- Cyclohexanedione enol ethers

When the enol ether 184 of 1,2-cyclohexanedione is ozonolyzed, instead of the normal ozonide 185 one obtains the product 186 of an intramolecular cross-ozonation which was also synthesized as the normal ozonide from methyl 1-cyclopentenecarboxylate 187 (Scheme 63). 

Irradiation of isophorone and a 15-fold excess of enol ether 177 results in the formation of a diastereomeric mixture of adducts 178 in quantitative yield. On brief treatment with tetrabutylammonium fluoride, the mixture of photoadducts 178 undergo cyclobutane ring-opening to give two epimeric diketo esters 179 in 70% yield. The Claisen condensation of these diketo esters proceeds on treatment with sodium hydride in refluxing THF, and a single enolized trione 180 is isolated in good yield. This photochemical approach provides easy access to a series of bicyclic 1,3-cyclohexanediones. 

The synthesis of the 19-nor analog (83) of Sarett s ketone also takes place via nonaromatic intermediates, being carried out in accordance with Scheme 63 [663, 664]. The cyclic diene (77) required for the synthesis was obtained from the ethyl enol ether of 1,3-cyclohexanedione (76) by the Normant reaction and transketalization with ethylmethyldioxolan. Conden-... 

Acidification of the residual aqueous solution followed by extraction with ether permits the isolation of about 1 g. of the enol form of 3,5,5-trimethyl-l,2-cyclohexanedione (see Note 3). 

If the organic layer is dried over magnesium sulfate and fractionally distilled at this point, both 2,4,4-trimethylcyclo-pentanone and 2-formyl-2,4,4-trimethylcyclopentanone, b.p. 49-50° (2 mm.), By 1.4495, may be isolated. The pot residue from this distillation contains a small amount of the enol form of 3,5,5-trimethyl-l,2-cyclohexanedione which crystallizes from petroleum ether as white needles, m.p. 92-93°. 

---