Chromanones 4-hydroxy

Chromanone, 3-acetamido-2-methyl-reduction, 3, 729 Chromanone, 3-amino-synthesis, 3, 734 Chromanone, 3-arylidene-thermoisomerization, 3, 722 Chromanone, 3-benzylidene-thermolysis, 3, 728 Chromanone, 3-bromo-2-hydroxy-benzofuran from, 3, 729 Chromanone, 6,8-dimethyl-hydroxymethylation, 3, 731 Chromanone, 2,3-epoxy-as synthon, 3, 735... 

The mechanisms of the cyclisation of 2 -hydroxychalcone derivatives which can lead to flavanones, flavones and aurones have been reviewed <95MI1> and the formation of 3-hydroxy- chromanones and -flavanones from l-(2-hydroxyphenyl)-2-propen-l-ones via the epoxide has been optimised <96JOC5375>. 

Kohar, I. Southwell-Keely, P. T. Reduction of 8a-hydroxy-2,2,5,7 8-pentamethyl-6-chromanone. Redox Report 2002, 7, 251-255. 

Chromanones,4 In the presence of this amine 4-mcthyl-6-hydroxy-2-pyrone (1) undergoes decarboxylative dimerization to form a coumarochromanone (2) in 42 yield. The pyrone group in 2 undergoes decarboxylative Diels Alder reactions (8, 32G 9, 175 176) with acetylenes to form 4-chromanoncs (3). 

The rings in the reduced chromanone (174) are cis- fused and the pyranone ring is chair-shaped. The axial 2-hydroxy group is intermolecularly hydrogen bonded to the carbonyl group (81JCS(P1)1096). 

Dehydration of isochromanols has to be carried out with care because of the relative ease with which the resulting isochromenes undergo polymerization under acidic conditions. Potassium hydrogen sulfate is a suitable reagent in some cases, and p-toluenesulfonic acid has also been used (71MI22400). The initial hydroxy compounds are available from iso-chromanones by reduction or by the action of a Grignard reagent. 

The catalytic reduction of some chromanones has been shown to yield mixtures consisting largely of 4-hydroxy-1-oxadecalin, together with significant amounts of 1-oxadecalin and... 

The compounds covered in this section include dihydropyranones, tetrahydropyranones and their benzologues (dihydrocoumarins, chromanones and isochromanones). The area of greatest interest is undoubtedly the chromanones because of their relationship to a number of natural products and presumably also because of their ease of formation, stability and value as precursors of other heterocycles. Tetrahydropyran-2-ones comprise one of those nebulous areas of heterocyclic chemistry and usually feature in text books as 5-lactones under derivatives of hydroxy acids. 

A 2,2-disubstituted chromanone results from the condensation of o-hydroxyacetophenone with diethyl oxalate. The initially formed 1,3-diketone cyclizes spontaneously to ethyl 2-hydroxy-4-oxochroman-2-carboxylate (77LA1707). The enolate also reacts with aliphatic ketones to give 2,2-disubstituted chroman-4-ones via the diol (79TL3685). 

Coumarins and isocoumarins appear to be of varied origins. Simple coumarins, such as umbelliferone, are formed by the shikimic acid pathway in which hydroxylation of p-hydroxycinnamic acid occurs. Other coumarins, for example alternariol (690), are derived from a polyketide unit, as are a number of chromanones, chromones, pyranones and isocoumarins (B-78MI22400). The biosynthesis of 5-hydroxy-2-methylchromone has been shown to involve the chromanone (60JCS654). However, isocoumarins are also derived from the mixed acetate-shikimate route, through initial cyclization of the polyketide and subsequent lactonization. 

With the enantioselective intramolecular benzoin reaction established as a synthetic tool, and in combination with our efforts in the synthesis of bioactive natural products bearing a quaternary a-hydroxy ketone unit (Davis and Weismiller 1990 Heller and Tamm 1981), such as the 4-chromanone derivative (S)-eucomol (Bohler and Tamm 1967 Crouch et al. 1999), a catalytic asymmetric synthesis of various 3-hydroxy-4-chromanones brought about by the chiral triazolium salts 127, 123b and 102 as pre-catalysts was investigated (Enders et al. 2006d). The sterically different pre-catalysts were chosen in order to adjust the catalyst system to the steric and electronic properties of the substrates 128. A screening of the reaction conditions indicated 10 mol% of the... 

Ishikawa et al. reported that ( )-quinine-catalyzed asymmetric intramolecular oxo-Michael addition (IMA) of 7-hydroxy-8-tigloylcoumarin gave cis-2,3-dimethyl-4-chromanone systems with high enantioselectivity and moderate diaster-eoselectivity, especially when chlorobenzene was used as a solvent. " Therefore, total synthesis of (+)-calanolide A (1) was achieved by application of the (—)-quinine-catalyzed asymmetric IMA. However, the synthetic route starting from 1,3,5- trimethoxybenzene was too long (13 steps with 3.5% overall yield) to practice. Finally, the authors improved and shortened the original synthetic route by application of Mgl2-assisted demethylation. 

Oxidation of chroman-4-one and its thio analogue with Mn(OAc)3 gives the 3-acetates and subsequent basic hydrolysis yields the 3-hydroxychroman-4-one. Enzymatic hydrolysis of the 0-heterocycle using Amano PS lipase in a phosphate buffer selectively cleaved the (+)-isomer <03TA1489>. Enol ethers derived from chroman-4-one are converted into the 3-hydroxy-chromanone with high enantioselectivity, optimal with the pentyl ether, using a modified Sharpless asymmetric dihydroxylation reaction <03JOC8088>. 

SYNS 1,2-BENZODiHYDROPYRONE (FCC) 2-CHROMANONE DIHYDROCOUMARIN 3,4-DIHYDROCOUMARIN o-HYDROXY-HYDROCIN-NA.MIC ACID-A-LACTONE FEMA No. 2381 MEULO-TIN MELILOTOL NCI-C55890 2-OXOCHROMAN... 

In contrast to thionyl chloride, which is commonly used as a reagent in organic synthesis, the application of seleninyl chloride (112) is limited to a few reactions. Thus, the new selenium-bridged chromanones 113 were prepared by the condensation of this chloride with enaminones of the 2-hydroxy-phenylethanone type 114 [57] (Eq. 24). 

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