O-hydroxychalcones

Synthesis ol benzopyran-4-ones (llavones) (rom o-hydroxychalcones or from benzoturan-3-ones... 

Bravo et al. reported that the carbonyl-stabilized arsonium ylides reacted with -hydroxybenzaldehydes to give o-hydroxychalcones (12). 

Thus, the alternative direction of the reaction of or o-hydroxychalcone 5 is not associated only with a specific influence of hydroxyl group, but most likely is due to several other reasons. Indeed, the presence of a hydroxyl group in other fragments of an unsaturated ketone does not change the reaction direction. 

Oxidation of o-hydroxychalcones (90) using PIDA under basic conditions (KOH-MeOH) affords cis- or trans-3-hydroxyflavanone (91) selectively via its dimethylacetal [69] [Eq. (20)]. 

Synthesis of benzopyran-4-ones (flavones) from o-hydroxychalcones or from benzofuran-3-ones (see 1st edition). 

A solvent-free synthesis of flavones has been achieved that simply involves the MW irradiation of o-hydroxydibenzoylmethanes adsorbed on montmorUlonite KIO clay for 1-1.5 min. Rapid and exclusive formation of flavones occurred in good yields (Scheme 8.61) [165]. The intramolecular Michael addition of o-hydroxychalcones on a silica gel surface has also been reported [166]. 

These same compounds (149 R = aryl) have also been prepared from o-hydroxychalcones and ethylenediamine <88MI 906-01 >. 2,3-Dihydro-5,7-dimethyl-l,4-diazepine is obtained in 56% yield on heating 4-phenylsulfonyl-3-penten-2-one with ethylenediamine at 100 °C in the absence of solvent <85JHC405>. This reaction provides an alternative to the vinamidinium route to 5,7-disubstituted-1,4-diazepines described above. The phenylsulfonyl groups of 2,3-bis(phenylsulfonyl)-l-propene (150) both activate the double bond to Michael addition and behave as a leaving group. These... 

In particular, the key intermediate product 381 in the synthesis of wighteone was prepared by the oxidative rearrangement of 3 -iodotetraalkoxychalcone 380 [474] and the key step in the synthesis of ( )-indatraline involved the HTIB-promoted diastereoselective ring contraction of a 1,2-dihydronaphthalene 382 to construct the indane ring system 383 (Scheme 3.152) [475]. A similar oxidative rearrangement of 3-cinnamoyl-4-hydroxy-6-methyl-2/7-pyran-2-ones with HTIB in dichloromethane followed by cycliza-tion was used by Prakash and coworkers for the direct conversion of o-hydroxychalcones into isoflavone derivatives [476]. 

A selenium dioxide induced oxidative cyclization of the 2 -hydroxychalcone 745 is a key step in the total synthesis of ( )-5 -methoxyhydnocarin-D (Scheme 189) <2005T4149>. DMSO containing catalytic amounts of iodine also effectively promotes the oxidative cyclization of 2 -hydroxychalcones to afford flavones <1996CHEC-II>. The DMSO-iodine mediated cyclization of the bis(2 -hydroxychalcone) 746 is a key step in the synthesis of the natural atropisomer4 4 ",7,7 -tetra-O-methylcupressuflavone (Equation 298) <1997TL1087>. Likewise, silica gel supported indium(in) halides catalyze the oxidative cyclization of 2 -hydroxychalcones to afford flavones in excellent yield (Equation 299) <2005TL253>. 

A wide range of 4-thio-substituted 2-aryl-4H-chromenes is formed when 2-hydroxychalcone derivatives react with various thiols (Scheme 27). Two new C-S and C-O bonds are formed in this catalyst-free domino reaction (13T2430). Chiral phosphoric acids catalyze the photocyclization reduction of 2-hydroxychalcones (13CEJ13658) and the 1,4-reduction of racemic 2,4-diaryl-2H-chromen-2-ols (13CEJ9775), both in the presence of the Hantzsch ester, to provide 2,4-diaryl-4H-chromenes in good yields and with excellent enantioselectivity. 

Pears (Pyrus communis) were cultivated by the Phoenicians and later by the Romans. There are now in excess of 500 named varieties worldwide. The total phenolic content of some cultivars of pears has been shown to be between 1235 and 2500 mg/kg in the peel and 28-81 mg/kg in the flesh (Galvis-Sdnchez etal. 2003). The phenolic composition of pears is very similar to that of apples containing 5-0-caffeoylquinic acid, 4-O-p-coumaroylquinic acid, procyanidins and quercetin glycosides. The main difference in the phenolic content of apples and pears is the presence of hydroquinone glucoside (arbutin) (Figure 7.24) in pears and the hydroxychalcones in apples (Spanos and Wrolstad 1992). The average... 

Hydroxychalcone, SCI. co-Salicylideneacetophenone. co-o-Hydroxybenzylideneacetophenone. (2-Hydroxystyryl)phenyl ketone [644-78-0]... 

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