3-Benzyl-4-chromones

In a different approach dihydrochalcones have been transformed to 3-benzyl-4-chromones. Treatment of (37) with ethyl formate and sodium led to (38) which on hydrogenation and selective demethylation yielded racemic 4 -0-methyl-3,9-dihydropunctatin (18) (25). A modified method... 

Other possible intermediates are 3-benzyl-4-hydroxycoumarins. Starting from the parent compound (41) the reaction to 3-benzyl-4-chromone (42) is achieved in moderate yield by reduction with diborane, followed by oxidation with sodium bichromate in aqueous sulfuric acid 42). 

Chromone, 2-amino-3-chloro-synthesis, 3, 713 diacetate, 3, 714 Chromone, 3-aroyl-photochemistry, 3, 695 Chromone, 2-benzhydryl-3-benzoyl-photoenolization, 3, 695 Chromone, 3-benzoyl-2-benzyl-photoenolization, 3, 695 Chromone, 3-benzoyl-2-methyl-synthesis, 3, 823 Chromone, 2-benzyl-in photochromic processes, 1, 387 Chromone, 3-benzyl-photolysis, 3, 695 Chromone, 3-bromo-synthesis, 3, 828 Chromone, 3-bromoacetyl-ring opening, 3, 713 Chromone, 3-bromo-2-methyl-reactions... 

Several chromones such as 2-benzyl-3-benzoylchromone, 39, are photochromic, proceeding to relatively stable hydrogen-bonded enols such as 40.43S... 

Treatment of the chroman-4-one 1 with benzyl chloride in DMF at 100°C gave the corresponding benzyl ether 2. When the reaction temperature was raised to 153°C, however, the products obtained were the chromone 3 and the flavone 4. It was subsequently shown that the same type of rearrangement could be effected simply by heating 1 with benzyl chloride in DMF containing potassium carbonate. 

Chromone-3-carboxaldehydes react with benzylic ylides to yield diastereomeric mixtures of 3-styrylchromones in which the (Z)-isomer is predominant <03NJC1592> subsequent DA reactions with maleimides under microwave irradiation are stereoselective with the... 

Amino-5-(2-hydroxy-benzoyl)-E9b/2, 170f. [2-(CO-NH2) 4H-chromon + Guanidin] 2-Benzyl-5-nitro- E9b/1, 33 [0HC-CH(N02)-CH0 + Ar—acetamidine] Pyrimido l,6-a]benzimidazol ... 

The carbon chain functionalised with the chromone nucleus characterises the patented saccharin derivatives 412 as agents for treating disorders of the central nervous system. As an example, the synthesis of (R)-(-)-[2-[4- (benzyl [7-(benzyloxy)-6-methoxy-3,4-dihydro-2ff-chromen-2-yl]methyl-amino)-2-butynyl]-l,2-benzisothiazol-3(2ff)-one S,S-dioxide (412 = H,... 

Benzopyrylium Salts. - Dichloromethoxybutane has been used in the cycliz-ation of the benzyl phenyl ketone (134) to give (after addition of perchloric acid) the pyrylium salt (135). The latter reacted normally with methylamine to form the isoquinolinium salt (136). A complex series of transformations has been suggested to account for the formation of the pyrylium salt (138) by the reaction of the chromone (137) with malononitrile-acetic anhydride. ... 

Higher esters of oxalic acid have been used, as, for example, the butyl [60] and the phenyl [15, 61]. Phenolic ketones other than the acetophenones lead to 3-substituted chromone-2-carboxylic acids although the yields are sometimes lower propiophenones give 3-methyl acids [7,14, 55,62,63] and benzyl aryl ketones lead to 3-phenylchromone-2-carboxylic acids [55]. 

The benzyl ketones required for this synthesis are usually prepared by a Hoesch reaction between a benzyl cyanide and a mono- or poly-hydric phenol. When the benzyl cyanide is labelled with isotopic carbon at the nitrile group, it is possible to prepare a C-4 labelled chromone [80] which may be useful in further metabolic studies (Figures 2.3). 

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