Enones cyclic, from diketone

Cyclic enone, 12 185 Cyclic ethers, 10 567, 569 12 663 polymerization, 14 271 Cyclic fatigue, in ceramics, 5 633-634 Cyclic gas generators, 6 786-787, 789, 827 Cyclic halides, 19 56 Cyclic hexakis(thio-l,4-phenylene), melt polymerization of, 23 705 Cyclic hydrocarbons, 13 687 Cyclic hydroxyalkyl alkyl peroxide, 18 454 Cyclic ion exchange operation, 14 408-413 Cyclic ketones, 12 176, 177 14 590-592. See also Cyclic 1,2-diketones physical properties of, 14 591t hydroxyalkyl hydroperoxides from, 18 450... 

MSA can be used as a powerful, safe, and recyclable catalyst for the condensation reaction of cyclic 1,3-diketones with arylaldehydes (Scheme 3.25). Firstly, synthesis of 2,2-(arylmethylene)bis(3-hydroxycyclohex-2-enone) from reaction of cyclic 1,3-diketones with several aromatic aldehydes was expected, but, as can be seen from Scheme 3.25, under the given conditions, 2,2 -(arylmethylene)bis(3-hydroxycyclohex-2-enone) was not formed and cyclic 1,3-diketones with aldehydes were effectively cyclized to give 9-aryl-substituted 1,8-dioxooctahydroxanthenes. 

The photochemical reactivity of P-ketoesters is different form that of P-diketones. Irradiation of a P-ketoester in the presence of an alkene produces oxetane via the ketone carbonyl instead of the desired cyclobutane ring system. Therefore, it is necessary to covalently lock the ketoesters as the enol tautomers. To this end, silyl enol ethers, 129 and 132a, and enol acetates, 130 and 132b, were prepared, but these substrates still fail to undergo the desired intramolecular [2 + 2] photocycloaddition with olefins. The only new products observed in these reactions result from the photo-Fries rearrangement of the cyclic enol acetate (130 to 131) and cis-trans isomerization of both acyclic substrates 132a/b. However, tetronates are appropriate substrates for both intermolecular and intramolecular photocycloadditions with olefins. In addition, enol acetates and silyl enol ethers of p-keto esters are known to undergo [2 + 2] photoaddition with cyclic enones (vide infra). 

An intramolecular variant of this process allows preparation of the cyclic diketones 197 from starting yn-enones (Scheme 87) [125]. Some typical ex-... 

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