Pyridinium ylids in synthesis. I. Alkylation of ylids and synthesis of ketones and acids.

Ylids generated by bases from pyridinium salts containing an activated methylene group can be C-alkylated in aprotic solvents. Reductive cleavage of the pyridine residue then affords alkylated ketones or esters. The reaction sequence constitutes an overall synthesis which is formally analogous to syntheses from β-keto esters. Alkylation of N-pyridinium phenacylid with phenacyl bromide gave chiefly 1,2,3-tribenzoylpropene, the tautomerism of which was examined.