6- Ethyl-3- chromone

Chromone-2-carbaldehyde, 3-methyl-synthesis, 3, 709 Chromonecarbaldehydes Knoevenagel condensation, 3, 711 Chromone-3-carbaldehydes mass spectra, 3, 615 oxidation, 3, 709 reactions, 3, 712 Schiff bases, 3, 712 synthesis, 3, 821 Chromone-2-carbonyl chloride Grignard reaction, 3, 711 Chromonecarboxamide, N-tetrazolyl-antiallergic activity, 3, 707 Chromone-2-carboxylic acid, 3-chloro-ethyl ester... 

Chromone-2-carboxylic acid, 8-cyano-6-methyl-ethyl ester... 

Grignard reaction, 3, 711 Chromone-2-carboxylic acid, 7-phenyl-ethyl ester reduction, 3, 704... 

A modification of the K-R reaction was introduced by Mozingo. This method involved reacting an o-hydroxyacetophenone with an ester in the presence of metallic sodium to form a 1,3-diketone. Treatment of the diketone with an acid then delivered the chromone via an intramolecular cyclization reaction. This method was applied to the preparation of 2-ethylchromone (21). 0-hydroxyarylketone 22 was allowed to react with ethyl propionate (23) in the presence of sodium metal.The resulting sodium enolate was then quenched with acetic acid to deliver the 1,3-diketone 24. Upon heating 24 in glacial acetic acid and hydrochloric acid, 2-ethylchromone (21) was delivered in 70-75% overall yield. 

Alkylation of the dihydroxyacetophenone, 44, with epichloro-hydrin results in condensation of two molecules of the phenol with the latent glycerol (45). Reaction of the intermediate with ethyl oxalate affords the chromone ester, 46. Saponification leads to the bronchiodilator cromoglycic acid (47). The agent is usually administered by oral insufflation as its extremely insoluble disodium salt. 

This was later extended to the synthesis of novel pyrimido-[l,3-a]-pyrimidines under solvent-free conditions ethyl-2-armno-4-aryl-l,4-dihydro-6-phenylpyrimidine-5-car-boxylates react regioselectively with 3-formyl chromone or diethyl (ethoxymethylene) malonate, without solvent, to afford pyrimido-[l,3-a]-pyrimidines [92] (Scheme 8.66). 

A similar route to 3-substituted chromones and isoflavone (R = Ph) Scheme 5.10 relies upon a Claisen-Hke condensation between the enolate of a 2-hydroxyphenyl ketone and ethyl formate (methanoate) (Scheme 5.11). 

This chromone has been prepared by the condensation of ethyl propionate with o-hydroxyacetophenone using sodium.2,3... 

A bromine atom on the benzene ring of chromones takes part in the Rosenmund-von Braun reaction to give moderately good yields of the nitrile, for example ethyl 8-cyano-6-methylchromone-2-carboxylate (545) (72JCS(Pl)779). Iodochromones and iodoflavones undergo the Ullmann reaction to form bis-compounds, some of which occur naturally or are related to such biflavonoids (B-75MI22302, 72JMC583). 

An unusual oxidative breakdown of a p-tolyl group to a carboxylic acid (688) is accomplished in moderate yield without degrading the chroman system (51JCS76) and the stability of this system to oxidation (cf. chromone, Section 2.23.9.3) is further illustrated by the conversion of an ethyl to a carboxyl group in the formation of 2,4,4-trimethylchroman-2,7-dicarboxylic acid (689) (57JCS3060). 

A chlorocarbonyl group ortho to a fluorine atom activates the halogen towards nucleophilic displacement. In the synthesis of a number of polyfluorinated chromones the 1,3-diketo side-chain is introduced using ethyl acetoacetate in the presence of magnesium ethoxide. Cyclization occurs on addition of sulfuric acid (70JOC930). 

A number of 2,3-fused chromones have been prepared from ethyl chloroformate and acetylsalicylic acid, a source of the mixed anhydride of formic and salicylic acids, and piperidinocycloalkenes (69JCS(C)935). A plausible mechanism is outlined in Scheme 165. It has not proved possible to isolate the chromanone (460) but the formation of 3-acetyl-2-methylchromone from 2-pyrrolidinopropene lends support to the intermediacy of the chromanone. The migration of the acyl group from oxygen to carbon is supported by the synthesis of 3-benzoyl-2-methylchromone rather than 3-acetylflavone from benzoylsalicylic acid and the pyrrolidinopropene. 

The introduction of a substituent into ethyl acetoacetate is reported to favour the formation of chromones (31JCS2426) though this is not always the case. 

However, the 1,3-diketone (470) has been isolated from the high temperature reaction between 3-dimethylaminophenol and ethyl benzoylacetate (64CR(259)1645>. Subsequent cyclization with acid yielded the chromone. It is likely that the hydroxydiphenylketone arises... 

Acetic acid, (3,5,6-trichloro-2-pyridinyloxy)-as herbicide, 2, 513 Acetic formic anhydride chromone synthesis from, 3, 820 Acetoacetic acid ethyl ester... 

Benzopyrylium perchlorate, 3-ethyl-reduction, 3, 662 Benzopyrylium salts 13C NMR, 3, 590 chromene synthesis from, 3, 756 chromone synthesis from, 3, 829 electrophilic substitution, 2, 49 mass spectra, 3, 618 reactions... 

Bromo 4-hydroxy-2//-chromene-2-thione 769 can be converted to the corresponding 2-(ethylthio)chromone upon treatment with ethyl iodide in the presence of K2C03 (Equation 318) <2004BML6083>. 

Kumar et al. were successful to hydrogenate 2-substituted thiochromones (113) to thiochromanones (114) with use of an excess amount (30 wt%) of 10% Pd-C in ethyl acetate at room temperature, although the chromones with an electron-donating sub-... 

Treatment of enamines with the mixed anhydride 213 obtained from acetylsalicylic acid and ethyl chloroformate yields chromones 214 (equation 90) thiochromones are similarly produced from S-acetylthiosalicylic acid112. 

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