O-Acetylbenzoic acid

Cyclization reaction. The reagent, 90% acid provided by Pennsalt Manufacturing Co., was used to effect condensation of o-acetylbenzoic acid (I) with 1,2-dimethoxy-... 

Diphenylphosphoryl azide and triethylamine added to a soln. of o-acetylbenzoic acid in benzene at room temp., and stirred for several days - 3-azido-3-methylphthalide. Y 79%. F.e. and method (with NaNj, BU4NN3 or MejSiNj), also decomposition of the products, s. H. Takeuchi, S. Eguchi, J. Chem. Soc. Perkin Trans. I 1988, 2149-54. 

An initially cooled stirred mixture of phthalic anhydride, dry malonic acid, and triethylamine warmed to 80°, after 2.5 hrs. when gas-evolution has ceased cooled, poured into water, and 20%-HCl stirred in o-acetylbenzoic acid. Y 90%. M. S. Newman, S. Venkateswaran, and V. Sankaran, J. Org. Chem. 40, 2996 (1975). 

A mixture of phenylalanine, o-acetylbenzoic acid, acetic acid, and toluene refluxed 48 hrs., while the aq. condensate passes through a Dean-Stark trap -> N-protected phenylalanine (Y 82%) added to a mixture of 85%-hydrazine hydrate, acetic acid, and water, then refluxed 5 hrs. phenylalanine (Y 80%). F. e. s. C. A. Panetta and A. L. Miller, Synthesis 1977, 43. 

A recent application of the same principle deals with o-formylbenzoic and 6>-acetylbenzoic acids. These compounds exhibit ring-chain tauto-merism, the possible form for o-formylbenzoic acid being as follows ... 

Benzofuran-3(2/f)-ones (396) exist in the keto form but undergo ready enolization. Acetylation with acetic anhydride and sodium acetate affords 3-acetoxybenzo[6]furans, but reaction under acidic conditions usually supplies these products admixed with 3-acetoxy-2-acetylbenzo[6]furans. Alkylation usually furnishes a mixture of O- and C-alkylated products. 3-Acetoxy-6-methoxy-4-methylbenzo[6]furan, on Vilsmeier reaction, supplies the 3-chlorobenzo[6]furan-2-carbaldehyde, the product expected from an enolizable ketone (72AJC545). Benzofuran-3(2//)-ones react normally with carbonyl reagents. Grignard reagents react in the expected way and dehydration of the intermediate affords a 3-substituted benzo[6]furan. The methylene group is reactive so that self condensation, condensation with aldehydes and ketones and reaction with Michael acceptors all occur readily. 

Selenophenes (195) have been obtained by the condensation of phenacyl bromides with /S-aminovinyl selenoketones, readily obtained from chloroimmonium salts (194) (76S521). The reaction of o-methylselenobenzaldehyde with chloroacetone gives directly an excellent yield of 2-acetylbenzo[6]selenophene (196) (72BSF1643). However, the reaction with bromoacetic acid yields not only the corresponding 2-carboxylic acid (197), but also the self-condensation product (198). 

Cyclization of appropriate o-(telluroether)benzaldehydes in presence of pyridine and acetic anhydride gives 2-acetylbenzo[6]tellurophene (28) and benzoU>]tellurophene-2-carboxylic acid (29). The acid is then decar-boxylated to benzol A] tell urophene (27) by heating with copper in quinoline. 

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