O-Hydroxy-acetophenone

C. Flavone. To a solution of 16.6 g. (0.069 mole) of the crude diketone in 90 ml. of glacial acetic acid, contained in a 250-ml. conical flask, is added, with shaking, 3.5 ml. of concentrated sulfuric acid. The mixture is heated under a reflux condenser on a steam bath for 1 hour with occasional shaking and is then poured onto 500 g. of crushed ice with vigorous stirring. After the ice has melted, the crude flavone is collected on a filter, washed with water (about 1 1.) until free from acid, and finally dried at 50°. The yield of product is 14.5-15 g. (94-97%) m.p. 95-97°. The over-all yield of flavone based on o-hydroxy-acetophenone is 59-68%. The product may be recrystallized from ligroin as in Method 1. 

Benzoylation, of o-hydroxy-acetophenone, 32, 72 of malonic ester, 37, 20 with benzoic-carbonic anhydride,... 

The tendency for antimony to achieve CN six is shown by the behaviour of organohaloantimony(V) compounds to substitution by oxo ligands. Jha et al.93 have employed the bidentate ligands acetylacetone, 8-hydroxyquinoline, salicylaldehyde, o-hydroxy-acetophenone and 2-hydroxynaphthaldehyde HL (equation 22). 

A relevant neighbouring group participation was noted in the oxidative cyclization of o-hydroxy-acetophenone [23] and o-hydroxy-dibenzoylmethane. 

Benz[6]indeno[2,l-e]pyrandiones are readily available by the acylation of o-hydroxy-acetophenone with monomethyl phthalate and subsequent Baker-Venkataraman rearrangement <02TL4515>. 

PA, phenyl acetate o-HAP, o-hydroxy acetophenone p-HAP, p-hydroxy acetophenone PH, phenol CA, catechol HQ, hydroquinone AA, acetic acid. 

This type of reaction was first used by Dilthey and Fischer69 in connection with the mechanism of the type in Section II, D, 2. By analogy with the well-known formation of benzopyrylium salts from methyl(ene) ketones and o-hydroxybenzaldehyde or o-hydroxy-acetophenone,340 benzoylacetone (84, R = Me, R = H, R" = Ph) and acetophenone (85, RIV = Ph, R" = H) afforded in the presence of acetic anhydride and sulfuric acid, 2-methyl-4,6-diphenylpyrylium sulfoacetate. The interesting feature of this reaction is that a unique product is obtained (i.e., only the carbonyl group of the diketone adjacent to the phenyl enters the condensation, although two such groups are available) R and R" could be reversed, but they are not.69-69 Similarly, dibenzoylmethane (84, R = R" = Ph, R =H) afforded 2,4,6-triphenylpyrylium with acetophenone in 80% yield.69... 

Banerji Goomer [116] introduced a general method for the synthesis of flavones in which the key step of the synthesis was the aroylation of O-hydroxy-acetophenones (236) to / -ketones (237) using very mild reaction conditions [Fig. (5)]. Subsequent cyclization of 237 yielded flavones (238) and the authors succeeded in preparing a series of 7 flavones in yields of between 84-91 %. More recently Bois et al., [117] using a similar approach but with improved reaction conditions synthesised 5-hydroxyflavones in a single step reaction from 2,6-dihydroxyacetophenone by treating with aroyl chloride in the presence of excess base. 

Kim et al. have transformed successfully MBH acetates into o-hydroxy-acetophenone derivatives via treatment with 1,3-dicarbonyl compounds in the presence of K2CO3 (Scheme 3.78). 

Acetophenone electrolyzed at room temp, in 1 2 trifluoroacetic aciV/-methylene chloride containing tetraethylammonium fluoroborate at a Pt-anode o-hydroxy-acetophenone. Y 85%. F. e., also ar. acylaminatioii (cf. Synth. Meth. 29, 334), s. Y.-H. So, J.Y. Becker, and L.L. Miller, Chem. Common. 1975, 262. 

Dialkylchroman-4-ones are readily prepared from enolates of o-hydroxy-acetophenones and ketones (Scheme 50). ... 

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