5.7- Dihydroxy-4-chromone

Chromone, 2,3-dichloro-7-methoxy-synthesis, 3, 825 Chromone, dihydromass spectra, 2, 23 Chromone, 3,5-dihydroxy-2-methyl-selective methylation, 3, 716 Chromone, 5,7-dihydroxy-2-methyl-prenylation, 3, 716 Chromone, 3,7-dimethoxy-2-methyl-reactions... 

D-Xylose and D-arabinose have been treated with a 0.5 M acetate buffer (pH 4.5) at reflux. Besides 2-furaldehyde, some catechols and unique chromones were isolated from the reaction mixture in small proportions. These included 3,8-dihydroxy-2-methylchromone and its precursor, 5,6,7,8-tetrahydro-3,5-dihydroxy-2-methyl-8-oxochromone. A trihydroxy-2-methylchromone was also isolated from the D-xylose reac-... 

The formation of such chromones as 3,8-dihydroxy-2-methyl-chromone by treating uronic acids or pentoses with dilute acid was reported by Aso,119 and studied by Popoff and Theander,120 who obtained a number of these compounds in 3.5% yield, as well as some catechols. Although nothing is yet known about the mechanism of formation of these compounds, the fact that the chromones contain 10 carbon atoms and are produced both from pentoses and uronic acids suggests that they may be derived from 2-furaldehyde or re-ductic acid, or produced from a decarboxylated intermediate. 

Dimer of 3,4-dihydro-4-(4 -hydroxyphenyl)-7-hydroxycoumarin. No data of the positive control (92) was reported. 6 4,4 -Dihydroxy-2,6-dimethoxydhihydrochalcone. c 5,7-Dihydroxy-3-(4-hydroxybenzyl)-4-chromone. 

Dimethoxycarbonyl- E6a, 152 (2-1 - 5-COOR — furan/Cu) Chromon 5,7-Dihydroxy-6-formyl-8-methoxy-2-methyl- E3, 106 (H - CHO)... 

PCS-catalyzed condensation of five molecules of malonyl-CoA to produce 5,7-dihydroxy-2-methyl chromone new to this plant (40). Another novel Aloe arborescens type III PKS that produces two hitherto unknown aromatic octaketides, SEK4 and SEK4b, has recently been reported (41). The application of plant cell cultures for the production of the polyketide hypericin from St. John s wort (Hypericum performatum, Hypericaceae) has been investigated (42). 

Some species in the Vicieae produce additional compounds to the main types. We found, for example, that the sweet pea, Lathyrus odoratus, proved to be almost unique in the tribe in synthesizing two 3-ethylchromones. Such chromones had not been found before in nature. Furthermore, one of them, 5,7-dihydroxy-3-ethylchromone, was significantly more fungltoxlc than plsatln (15). Last year, Fuchs and his co-workers at Wageningen (16) reported further phy-toalexlns in the sweet pea, two o-hydroxydlhydrochalcones, odoratol and methylodoratol. 

Fluoroalkyl chromone derivatives can be obtained from the base catalysed reaetion between 2,2-dihydropolyfluoroalkanoates and phenols. Initial loss of HF allows Michael addition of the phenol and subsequent cyclisation of the enol ether yields the heterocycle. m-Substituted phenols give the expected mixture of 5- and 7-substituted chromones, whilst dihydroxy aromatic compounds give polycyclic materials (94JFC263). In a more conventional approach Z-3-(aryloxy)-polyfluoroalkenoic adds, derived from Michael addition of phenols to polyfluoro-2-alkynoic acids, undergo intramolecular Friedel-Crafts acylation to 2-polyfluoro-alkylchromones (94JFC25). 

A more recent report on the use of PPE to promote cyclization of a P-naphthol has appeared. The reagent allowed product formation in excellent yield at room temperature. Such results were a great improvement to the reaction conditions and yield typically obtained in the Simonis chromone synthesis. 2,6-Dihydroxy-naphthol 35 gave chromone 36 in 98% yield. 

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