2,6-Dimethoxy-4-hydroxyacetophenon

Dimethoxy-4 -hydroxyacetophenone Pancratium biforum (Amaryllidaceae) [bulb] COX (PGS), 5-LOX... 

Trimethoxydiazoacetophenone undergoes acid-catalysed cyclization to give 4,6-dimethoxy-3(2/ )-benzofirranone. Under the same conditions diazoacetophenone gives the intermolecular product 2-hydroxyacetophenone. The difference in reaction mechanism was attributed to the interaction of o-OMe with the diazomethyl group. 

Condensation of 4,6-dimethoxy-2-hydroxyacetophenone with diethyl carbonate and an alkoxide ion has now been shown to give the coumarin-3-carboxylic ester (245), and not 4-hydroxy-5,7-dimethoxycoumarin (246), as originally reported. Heating the ester with aqueous alkali resulted in hydrolysis and decarboxylation to (246). The well-established acid cyclization of salicyl-aldehyde with ethyl cyanoacetate to give coumarin-3-carboxylic acids has been studied in alkaline media and found to give the ester (247 X = O) and the imino-ester (247 X = NH). When the proportion of the cyano-ester was increased, high yields of the latter were obtained. "... 

Cyclic voltammetry showed the electrochanical oxidation of 3,5-dimethoxy-4-hydroxyacetophenone gave 3,4-di-hydroxy-5-methoxyacetophenone as the major product by a one electron oxidation process (20% isolated yield), but 30-40% estimated by thin layer chromatography [2864]. 

Preparation by bromination of 2,4-dimethoxy-6-hydroxyacetophenone with cupric bromide in refluxing chloroform-ethyl acetate mixture [1845,2922], (62%) [2922]. 

This problem prompted the development of second-generation photoinitiators for radical polymerization, which do not possess benzylic H atoms, such as a,a-dimethoxy-a-phenylacetophenone (1), a,a-diethoxyacetophenone (2), and the a-hydroxyacetophenone derivatives (3) and (4). These photoinitiators undergo photocleavage, in an analogous manner to benzoin ethers, as shown by various studies, " including free-radical trapping and laser flash photolysis. 

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