Pyrandione, pyrone

Acylated Meldrum s Acid Pyrandione Pyrone (Yield)... 

The procedure described here offers a general route to a variety of unsymmetrically substituted y-pyrones from Meldrum s acid.2 Substitution at the 2-position depends on the acid chloride chosen, while substitution at the 5-position is derived from the vinyl ether. A variety of substituted y-pyrones have been synthesized by utilization of this method as illustrated in the Table. The intermediate pyrandione is believed to arise through the addition of the vinyl ether to an acyl ketene that results... 

Reversibility of the spectral changes under irradiation and the photostability of the compound without the phenoxy substituent suggested a photochromic para-ana-quinone transformation of 9-phenoxy-pyrone (9-phenoxynaphthacene [12,11 -bc]-2,8-pyrandione) (Table 7.10, Scheme 22).48... 

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