Chromone-2-carbonyl chlorides

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-carbonyl chloride (496) reacts readily with a Grignard reagent to yield a ketone (497) without the need to add iron (III) chloride or to maintain the temperature at -70 °C (81JCS(P1)2552> as is customary in order to suppress the formation of f-alcohol. 

The preparation of chromone-2-carbonyl chlorides from the acid and thionyl chloride often leads to the trichloride (498) as a byproduct (61JGU523) but this is suppressed when a few drops of DMF are added (72JMC865) or phosphorus pentachloride and cyclohexane are used (73BSF2392). When the trichloride is treated with water, an amine or acid, it rearranges to 4-chlorocoumarin (499) (63JGU1806). 

Analogous results were observed in the Arbuzov reactions of chromone 2-carbonyl chloride with trialkyl phosphites (equation 21) In this case the acyl carbonyl group is... 

Reactions—There are four main synthetic uses for chromone-2-carbonyl chlorides ... 

Chromone-2-carbonyl chloride reacts with enamines to form ketones which may be cyclised with hydrazine to pyrazoles [32] such as (71) or (72) according to the conditions. 

Chlorocoumarin may be prepared by the reaction of chromone-2-carboxylic acid with thionyl chloride [169] or oxalyl chloride [55]. 4,4-Dichlorochromen-2-carbonyl chloride which is formed first, reacts with water to give a 91 per cent yield of 4-chlorocoumarin (92) with simultaneous release of carbon monoxide [161]. 

Addition of a proton to carbonyl oxygen produces a hydroxy-benzopyrylium salt chromones undergo this protonation more easily than the coumarins, for example passage of hydrogen chloride through a mixture of chromone and coumarin in ether solution leads to the precipitation of only chromone hydrochloride (i.e. 4-hydroxy-1-benzopyryhum chloride). O-AUcylation requires the more powerful alkylating agents ... 

The one-pot synthesis of 2-substituted-3-carboxychromones is readily attained by the reaction of 3-oxo-3-(2,6-di luorophenyl)propanoates and acyl chlorides (13CC5313) and of 3-[2-(methoxymethoxy)phenyl]propio-lates and aldehydes followed by DDQ oxidation of the formed chroma-nones (13T647), via transition metal-free approaches. Palladium(II) -catalyzed cascade carbonylative cyclization of 2-bromophenols and terminal alkenes gives chromones 44 in moderate to good yields. Variation on the amine used in the catalytic system led to aurones 45 as major products (Scheme 74) (13TL1802). 

Chromone-2-carbonyl azide (67) may be prepared in excellent yield either by adding sodium azide to a solution of the acyl chloride (68) in dioxan, or by the action of nitrous acid on the hydrazide (69) [157], A Curtius reaction on the azide led to an interesting series of derivatives of 2-aminochrbmone (70, R = OEt, Me, CCI3, NEta and similar groups), whose reactions have been studied [175-179]. 

The formation of the 4,4-dichlorochromen compounds which have been mentioned several times in this review, is another example of reaction at the pyrone carbonyl group. Thionyl chloride reacts with the pyrone group of chromone-2-carboxylic esters to give 4,4-dichlorochromen-2-carboxylates (81) [162], a reaction which may be reversed by means of aqueous sodium bicarbonate at room temperature [168]. 

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