Pyranones tetrahydropyran-4-ones

The fused tetrahydropyran-2-one (566) is obtained from 2-methylcyclohexanone by Michael addition to methyl prop-2-enoate and reduction of the resulting keto ester (565 Scheme 216) (63JOC34). When the enamine derived from the cyclohexanone reacts with the unsaturated ester, a mixture of keto esters (565) and (567) is formed. The pyranone (568) is formed by reduction of the latter. 

Pyran-4-ones tend to give complex mixtures on chemical reduction, but catalytic hydrogenation usually gives the tetrahydropyran-4-one or the corresponding pyran-4-ol (63CR(256)1542). The influence of solvent on the nature of the product is exemplified by the reduction of 2,6-dimethylpyran-4-one, which in ethanol affords the fully reduced pyranone,... 

A Nazarov cyclisation of l-(3,4-dihydro-2//-pyran-6-yl)-3-phenylpropenones affords cyclopenta[Z)]pyranones (Scheme 9) <03OL4931> and the conjugated ethoxytriene 7 derived from tetrahydropyran-2-one also yields a fused cyclopentenone <03JOC9728>. 

---