Chromanes and Chromones

Deriv Diacetyleugenitol, mp 200-202 °C, by acetylation of eugenitol with AC2O-H2SO4 StL Mycobiont of Lecanora rupicola (L.) Zahlbr. 

HPLC Ri 5 MC Figs. 50CD, 51A Lit Himeck 1972b Huneck et al. 1992a 

Deriv Methyl leprarate, prisms (MeOH), mp 132-133 °C, from lepraric acid with CH2N2 StL Lepraria latebrarum (Ach.) Arnold, Roccella fuciformis (L.) DC. 

Deriv Acetyllobodirin, needles (MeOH), mp 172-173 °C, from lobodirin with AC2O-H2SO4 StL Roccellina cerebriformis (Mont.) Tehler. 

2-Methyl-5-hydroxy-6-hydroxymethyl-7-methoxychromone (2-Methyl-5-hydroxymeth)4-7-methoxychromon) 

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Ellis GP (1977) The ehemistry of heterocyclic compounds chromenes, chromanes and chromones. In Weissberger A, Taylor EC (eds). Wiley, New York, Chap II, pp 11 139... 

Both coumarin and chromone are converted by diborane then alkaline hydrogen peroxide into 3-hydroxy-chroman." " Catalytic reduction of conmarin or chromone satnrates the C-C double bond." For both systems, hydride reagents can of course react either at carbonyl carbon or at the conjugate position and mixtures therefore tend to be prodnced. Zinc amalgam in acidic solntion converts benzopyrones in 4-unsubstituted benzopyrylinm salts." ... 

Cyclobuta[fc]chroman-4-ols, derived from chromones by a [2+2] photocycloaddition to ethylene, are prone to acid-catalysed rearrangements. Elaboration of the parent system prior to rearrangement has enabled the marine sesquiterpene filiformin <96JOC4391>, the henzo-1,3-dioxan nucleus of averufin <96JOC9164> and cyclobuta[h][l]benzoxepin-8,9-diones <96CC1965> to be synthesised. 

In contrast to the benzoannelated nitrogen heterocycles, only a few kinds of benzoannelated systems without nitrogen have been described (Fig. 3.15). Five-mem-bered rings such as benzo[b]furans (336) [184, 461] and hydrobenzo[b]furans (337) (Scheme 3.41) [337, 462, 463] and six-membered rings like 4H-l-benzopyran-4-ones (4-chromones) (338) and 2H-l-benzopyran-2-ones (coumarines) (339) [96, 464, 465] 2,3-dihydro-4H-l-benzopyran-4-ones (chroman-4-ones) (340) [466] and 3,4-dihydro-lH-2-benzopyrans (isochromans) (341) [444] have been reported. 

The I3C spectra of chroman-4-ones are similar to those of the corresponding chromone, although the C-2 and C-3 resonances occur at much higher field, as expected of methylene... 

The directing effect of a substituent in a chroman is sometimes different from that in chromone for example, bromination of the 7-methoxy compounds yields the 8-bromo-chromone not the 6-bromochroman, and nitration of 8-hydroxychromone gives mainly the... 

An unusual oxidative breakdown of a p-tolyl group to a carboxylic acid (688) is accomplished in moderate yield without degrading the chroman system (51JCS76) and the stability of this system to oxidation (cf. chromone, Section 2.23.9.3) is further illustrated by the conversion of an ethyl to a carboxyl group in the formation of 2,4,4-trimethylchroman-2,7-dicarboxylic acid (689) (57JCS3060). 

Salicylaldehyde also reacts with enamines to form chromans, although these have not usually been isolated but rather have been oxidized directly to a chromone (66JOC1232). The synthesis has been applied to both cyclic and acyclic enamines and to 2-hydroxy-1-naphthaldehyde. The initial intermediate undergoes an intramolecular cyclization involving participation of the neighbouring hydroxyl group. 

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. 

The total reduction of the enone system present in chromone to the corresponding chroman is effected by hydrogenation and is a key step during the synthesis of 2-(aminomethyl)chromans (2-AMCs) for evaluation of their affinity for the dopamine (DA) D2 receptor <1997JME4235>. Luche reduction of a chroman-4-one is used during the synthesis of antagonists of leukotrine D4 <1998BML1791>. 

Rotenoids have a basic structural element involving fused chromone and chromane rings. The best-known rotenoid is the furanorotenoid rotenone (C501 Phe pyran-... 

The outcome of the reaction of phenols with 5-alkylidene Meldrum s acids 25 catalysed by Yb triflate in the synthesis of O-heterocycles is dependent upon the nature of the alkylidene unit. Two distinct Friedel-Crafts sequences are apparent in this mild and simple route to coumarins and dihydrocoumarins and to chromones and chroman-4-ones (i) C-alkylation - (9-acylation and (ii) C-acylation - (9-alkylation <06JOC409>. 

Chromone derivatives, in particular 2-spiro-chroman-4(lF/)-ones, are ubiquitous in nature and possess various biological activities which include antiarrhythmic, anti-HIV, antidiabetic, acetyl-CoA carboxylase (ACC) inhibitor, vanilloid receptor antagonist, growth hormone secretagogues, histamine receptor antagonist, and... 

Both flavanones and 2 -hydroxychalcones are oxidised to flavones in the absence of solvent by In salts supported on silica gel <05TL253> and the former also by Mn(OAc)3 <05SC2723>. Various 3-(perhaloacyl)chromones, which exist as a mixture with their covalent hydrates, have been obtained from 2-hydroxy-2-(perhaloalkyl)chroman-4-ones on heating with the formylating agent, diethoxymethyl acetate <05SL1164>. 

The dehydrogenation of 2 -hydroxychalcones and flavanones to flavones, of l-(2-hydroxyaryl)alk-2-en-l-ones and chroman-4-ones to chromones and of thiochroman-4-ones to thiochromones can be accomplished using iodine in hot DMSO <97HCM223>. E-3-Styrylchromones result from the oxidative rearrangement of 5-aryl-l-(2-hydroxyphenyl)penta-2,4-dien-l-ones with thallium(lll) nitrate <97LA2065>. Dimethyldioxirane converts flavanones into flavones by way of the 2-hydroxyflavanone. This approach enables flavans to be converted to a variety of flavonoids <97TL4651>. 

The iron-catalyzed synthesis of dihydro-2H-pyrans, 2H- and 4H-chromenes, chromones, isocoumarins and xanthenes were described in a broad review on the synthesis of heterocycles (14T4827), while the synthesis of 2H-pyran and chroman derivatives, coumarins and xanthone-type compounds was described in a review of recent progress on the chemistry of dimethyl acetylenedicarboxylate (14S537). The synthesis of several polysubstituted spirooxidole-2-amino-4H-pyrans, mainly through three-component reactions, was also described in a review on the synthesis of biologically active spirooxindoles (14T9735). 

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