Benzoic anhydride, Claisen condensation

Other methods of preparing flavone include the action of ethanolic alkali on 2 -acetoxy-a,/3-dibromochalcone 7 Claisen condensation of ethyl o-ethoxybenzoate and acetophenone, and cyclization of the resulting 1,3-diketone with hydriodic acid 8 and treatment of 3-bromoflavanone with potassium hydroxide in ethanol.9 Flavone has also been prepared from ethyl phenyl-propiolate by condensation with sodium phenoxide and subsequent cyclization with phosphorus pentachloride in benzene 10 by fusing o-hydroxyacetophenone with benzoic anhydride and sodium benzoate 11 by the dehydrogenation of 2 -hydroxychal-cone with selenium dioxide 12 and by the action of alkali on flavylium chloride.13... 

C-Acylations of C,H-acidic compounds have also been realized on insoluble supports. The few examples that have been reported include the C-acylation of support-bound ester enolates with acyl halides [9], Claisen condensations of polystyrene-bound ketones with benzoic acid esters, the C-acylation of nitriles with acyl nitriles or anhydrides, and the C-acylation of phosphonates with acyl halides (Entries 5-9, Table... 

An inspection of the mechanism of the condensation of ethyl isobutyrate with ethyl benzoate reveals that the essential feature of the acceptor molecule (ethyl benzoate) is that it be able to lose a negative ion (ethoxide ion in this case) in step 13 to form the 0-ketoester, Accordingly it has been found possible to carry out successful Claisen condensations between ethyl isobutyrate and other acceptor molecules such as benzoyl chloride, or benzoic anhydride.22 For all of these reactions we may generalize step 13 as follows ... 

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