4-Pyrones ring opening with base

Pyrones are in many ways best viewed as unsaturated lactones, and as such they are easily hydrolysed by aqueous alkali 4-pyrones, too, easily undergo ring-opening with base, though for these vinylogous lactones, initial attack is at C-2. ... 

The method described is that of Miles, Harris, and Hauser2 and is an improvement over the earlier procedure of Hauser and co-workers.3,4 In the earlier method the dianion of benzoylacetone, formed by the action of alkali amide in liquid ammonia, was treated with methyl anisate to yield 1 -(/>-methoxyphenyl)-5-phenyl-l,3,5-pentanetrione (61% based on the ester). This compo ir d has also been prepared by the base-catalyzed ring opening of 2 - f -mcthoxyphenyl) -6-phenyl -4 pyrone however, no yield is reported.5... 

A dihydro-derivative (4) of strobiline (M+ 193) was also obtained. In the mass spectrometer, the pyrrolidine ring is opened to give fragments of m/z 165 and 164 (base peak), followed by a retro-Diels-Alder reaction to give fragments of m/z 137 and 136, respectively. The location of the two additional hydrogen atoms was deduced from the relative u.v. extinctions of (3) and (4), which is consistent with the dihydro-y-pyrone skeleton in the latter compound. This was confirmed by 3H n.m.r. spectra that showed no vinylic protons. 

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