Enollactones carboxylic acids

Base-catalyzed cyclocondensation (a) of alkynones with malonic esters and (b) of 1,3-diketones with acetylenic acids yields esters 27 of 2H-pyran-2-one-3-carboxylic acid or 5-acyl-2H-pyran-2-ones 29, respectively. In both cases, Michael additions are the primary steps, which afford 5-oxopentenoic esters 26 or 28 providing the 2H-pyran-2-one system by enolization and enollactone formation [12] ... 

Acylketenes l-(AIkoxy)enolethers a-Alkoxymethyleneketones Carboxylic acid isopropenyl esters Enolesters Enollactols Enollactones a, p-Ethyleneacetals a,0-Ethylenelactones a-Hydroxymethyleneketones 3-Keto-l, 2-en-l-olethers 3-Keto-l,2-en-l-ols a-Oxidoalcohols a,P-Oxidoketones Vinyl esters... 

---