Chromone-3-carboxaldehydes 6-

Conversion of an aldehyde into a carboxyl group is effected with chromium trioxide-sulfuric acid in moderate yield. This is a synthetically valuable conversion because of the availability of chromone-3-carboxaldehydes (477). Photooxidation of the aldehyde (477 R = H, Me, Cl, OMe or OAc) in the presence of NBS gives high yields of 3-carboxylic acids (80SC889). 

Benzo[fe]xanthene-6,l 1,12-triones are readily available through the photo-induced 1,4-acylation of naphthoquinone with 2-hydroxybenzaldehydes followed by oxidation <02H(57)1915>. Chromone-3-carboxaldehyde reacts with o-benzoquinodimethane in a DA reaction with concomitant deformylation to give a diastereoisomeric mixture of tetrahydrobenzo[fc]xanthones oxidation can be accomplished with DMSO/I2 <02T105>. 

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... 

The —CH=C—CH=0 portion of chromone-3-carboxaldehydes acts as a heterodiene and adds on alkoxyethenes or dihydropyran to give usually (but not always) a mixture of stereoisomers differing in the configuration of C-3. The ratio of isomers varies but the ewdo-product predominates. Prolonged reaction at ambient temperature for 15 days may be necessary but in a sealed system, reaction progresses at 115°C over a couple of days [3164, 3054, 3055]. Heterodienes and their uses have been reviewed [B-42, 2455, 3067a, 3880]. 

The acid chlorides of several chromone-2-carboxylic acids have been used in the Freidel-Crafts reaction to prepare 2-aroyl-chromones which were pharmacologically active.Decarboxylation of a heterocyclic acid is often a facile reaction but removal of an aldehyde group is unusual. Chromone-3-carboxaldehyde (156) has been decarbonylated by heating with piperidine to give the acrylophenone (157), which cyclized again, with loss of piperidine and one carbon atom. ... 

Chromone-3-carboxaldehydes react with ethyl glycin-... 

Although chromone-3-carboxaldehyde is readily prepared, the 2-isomer is much less readily available. Selective reduction of methyl chromone-2-carbox-ylate with NaBH4 and MeOH has given the 2-hydroxymethyl compound, apparently without affecting the carbonyl group of the pyrone oxidation with... 

Terzidis M, Tsoleridis CA et al (2005) Chromone-3-carboxaldehydes in Diels-Alder reactions with indole-ortho-quinodimethane. Synthesis of tetrahydrochromeno[2, 3-b]carba-zoles. Tetrahedron Lett 46 7239-7242... 

Stephanidou-Stephanatou and co-workers reported a 4-picoline-catalyzed het-ero-Diels-Alder type cycloadditions of chromone-3-carboxaldehydes 124 with acetylenedicarboxylates 125, providing an one-pot synthesis of pyrano[4,3-c] chrotnenesl27, Scheme 3.42 [57],... 

Matha, M., Sundari, L.B.T., Rajanna, K.C., Saiprakash, P.K. Kinetics and mechanism of hydrogen peroxide oxidation of chromone-3-carboxaldehydes in aqueous acid and micellar media. Int. J. Chem. Kinet. 1996, 28(9), 637-648. 

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