Oxygen 2- alkyl-4-pyrones

Another ingenious route for the generation of the dipolar species involves the carbonyl-0-alkylation or 0-silylation of 3-oxygenated 4-pyrones. The example below shows 0-methylation of a kojic acid derivative, then deprotonation of the 3-hydroxyl using a hindered base to trigger the dipolar cycloaddition. 

O-Alkylation of pyridones can be effected with diazomethane 2-pyridone forms 2-methoxypyr-idine. Frequently O- and iV-alkylation occur together 4-pyridone with CH2N2 yields 4-methoxypyridine and l-methyl-4-pyridone. Et30+ and similar active alkylating agents also alkylate the carbonyl oxygen of pyridones and pyrones. 

As previously described, ethers can be alkylated photochemically at the carbon alpha to the ether oxygen. In compounds having both an ether and a carbonyl function a "competitive alkylation process may take place. Tetrahydro-y-pyrone can serve as a good model for this "competitive alkylation between a ketone and an ether. This molecule has a ketone function having two methylene groups at its alpha positions, and an ether function having also two adjacent methylenes. When tetrahydro-y-pyrone was left in sunlight with 1-octene the 1 1 adduct was obtained in about 70 % yield. Alkylation occurred at the carbon alpha to the carbonyl function (24) ... 

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