3-Hydroxy-2-arylacrylic acid ethyl ester

It has been shown that the lead tetraacetate-mediated 1,2-aryl shift of various meta-substituted / -cyclohexyl aryl ketones, e.g. (10), results in excellent yields of the corresponding rearranged esters (11). A unique reaction, providing 3-hydroxy-2-arylacrylic acid ethyl esters (14), has been observed between aryl aldehydes and ethyl diazoacetate in the presence of the iron Lewis acid [rj — (C5H5)Fe(CO)2(THF)BF4], It appears that the enol esters are formed by an unusual 1,2-aryl shift from a possible intermediate (13), which in turn is formed from the reaction of the iron aldehyde complex (12) with ethyl diazoacetate (see Scheme 4). 

Hossain et al have already found that the cyclopentadienyl dicarbonyl iron Lewis acid, [CpFe(CO)2(THF)] BF4 (108), catalyzes a variety of reactions including cy-clopropanation [34a], aziridination [34b], and Diels-Alder reactions [34c]. Recently, they have reported that the iron Lewis acid [CpFe(CO)2(THF)]+BF4 (108) catalyzed synthesis of 3-hydroxy-2- arylacrylic acid ethyl ester (106) [34d]. The product distribution of (108) is not affected in the presence of proton sponge, but is dependent on temperature and the nature of the substrate aldehyde. 

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