[5,6-Dihydro-6-methoxy-2H-pyran-3(4H)-one, a building block for the synthesis of CNS agents]

The phenyl-pyranyl-piperidin derivative 5, prepared from the title compound 2, shows a strong stimulating effect in animals. Reactions of 2 with 2-amino-phenylcarbonyl derivatives or phenylhydrazine can lead to [3,2-b] as well as [3,4-b] annulated pyranes. Regioselective reactions in 2- or 4-position of 2 are successful after conversion to the enamine 14a, the silylenolether 24 and the lithioenamine 29. Cycloadditions, cyclocondensations or electrophilic aldoleractions yield the pyrano-pyranes 16 and 19a, resp., or the hydroxybenzyl- and hydroxybenzylidenpyranes 25 and 30, resp.