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Dibenzopyranones

The dibenzopyranone ring system may be viewed as a chromone with an additional fused benzene ring and thus generally related to the antiasthmatic mediator release inhibitor cromolyn (see Chapter 11). Two dibenzopyranones have in fact been investigated for this indication in the clinic. Friedel-Crafts cyclization of the substituted cresyloxybenzoic acid (2-1) in sulfuric acid leads to the dibenzopyranone (2-2). The methyl group is then oxidized to a carboxylic acid by means of chromic acid. The acid is then converted to its sodium salt, xanoxate sodium (2-3) [2]. [Pg.516]

The reaction of phenols with alicyclic 1,3-dicarbonyl compounds in phosphorus oxychloride or sulfuric acid also leads to 3,4-fused coumarins (40JA2405). Dehydrogenation to the dibenzopyranone occurs on heating with sulfur or with palladium-charcoal (73CB62). [Pg.800]

Formation of the isochroman system is considered to trigger the synthesis of the dibenzopyran (17, X = H2) by the acid catalysed cyclisation of c/s-enediynes (16, X = H2). In a similar manner, the carboxyl function in (16, X = O) promotes cylisation to a dihydropyranone derivative which is followed by a Myers cycloaromatisation to the dibenzopyranone (17, X = O) (95TL9165). [Pg.281]

Directed remote metalation (DreM) of biaryl amides and O-carbamates, conceptually based on the complex-induced proximity effect (CIPE) [15] provides, especially in view of their link to transition metal-catalyzed cross coupling regimens [16], general and versatile routes to fluorenones (16 —> 15, Scheme 4) [5,17] and biaryl amides (16 —> 17) [18] whose features are overriding Friedel-Crafts reactivity and yield enhancement in comparison to Suzuki-Miyaura coupling routes for highly hindered biaryls, respectively. Additional features of the O-carbamate DreM result is potential further DoM of 17 with appropriate phenol protection and cyclization to dibenzopyranones [18]. [Pg.109]

Another approach to ring closure reaction is the o-arylation of substituted phenoxide ions by o-bromobenzonitrile followed by Si02-catalysed lacto-nization. The phenoxide ions of the amino acid (S)-tyrosine, protected as A, O-diacetyl methyl ester, does not racemize under the standard SRN1 conditions and can be used to obtain the optically active benzo[c]chromen-6-one (the O-acetyl is hydrolyzed in the reaction media to furnish the phenoxide ion) (Sch. 43). Racemic dibenzopyranones are obtained by the reaction of the anion from the TV-acetyl methyl ester of (R)-hydroxyphe-nylglycine with o-bromobenzonitrile 2-cyano-4,5-dimethoxybromobenzene (65 and 79% respectively) [110]. [Pg.520]

The Suzuki-Miyaura tactic carried out on solid support (Scheme 28) [52] provides routes to small libraries of condensed heterocycles. Thus, Merrifield resin with the LeznofF-linked bromobenzene derivative 78 undergoes cross-coupling under normal solution-phase conditions with boron pinacolate 79 or boronic acid 80, prepared by DoM, to afford phenan-thridines 81 or, via 82 and some manipulation, dibenzopyranones 83 in good yields and with high purities. The Stille solid-support reaction has also been successfully executed [53]. [Pg.346]

This anionic remote Fries rearrangement provides a general route to highly substituted biaryls 146 which, due to steric effects, may be difficult to prepare directly by Suzuki-Miyaura cross-coupling, as evidenced in the comparison with the synthesis of dibenzopyr-anones 147 (Scheme 39) [66]. The efficient acid-catalyzed cyclization to dibenzopyranones shows broad scope both for unusually substituted (148-150, Scheme 40) and various heterocyclic analogues (151-153, Scheme 40) [65, 67]. [Pg.353]

Scheme 40. Dibenzopyranones and heterocyclic analogues by anionic remote Fries rearrangement. Scheme 40. Dibenzopyranones and heterocyclic analogues by anionic remote Fries rearrangement.
Dibenzo[/>, J]pvran-6-ones are formed by the Pd-catalysed cyclisation of aryl 2-iodobenzoates, whereas 2-iodobenzyl arylacetates afford 3-aryldihydroisocoumarins under the same conditions <07T10889>. The same dibenzopyranones are formed by way of a Suzuki cross coupling involving functionalised salicylates, derived from a formal [3+3] cyclisation between l,3-bis(silyl enol ethers) and 3-silyloxy-2-en-l-ones, and subsequent lactonisation (Scheme 32). In a variant route, the pre-lactonisation biaryl is derived from the bis(silyl enol ethers) and 3-aryl-3-silyloxyenones <07JOC6255>. [Pg.415]

Stereoselective Preparation of Hexahydro dibenzopyranones and intermediates therefor... [Pg.88]

Archer, R.A. Day, W.A. Stereoselective Preparation of Hexahydro dibenzopyranones and Intermediates Therefor 1978 US 4,102,902 Archer, R.A. Lemberger, L. Hexahydro-dibenzo[b,d]pyran-9-ones as Antiasthmatic Drugs 1978 US 4,087,546... [Pg.177]

Dibenzo-/ -dioxins 1086 Dibenzodioxocines 1308, 1309, 1311 Dibenzofurans, formation of 1289, 1291 Dibenzopyranones, formation of 1257 Dibenzoylmethane enol, IR spectrum of 382... [Pg.1485]

A DoM-Suzuki-Miyaura cross-coupling combination was established [35a] for the construction of dibenzopyranones 102 (Scheme 14.23), aclass of condensed heterocycles represented in bioactive as well as naturally occurring molecule domains. [Pg.1101]

Thus, cross-coupling of the DoM-derived benzamide boronic acid 99 with bro-mobenzenes 100, which may also be prepared by DoM chemistry, furnishes biaryls 101 that under either HCl or BBrj/HOAc conditions produce the methyl ether or free phenol dibenzopyranones 102, respectively. Establishment of regiochemistry by DoM in the thereby derived biaryls 103 and hence the unusually substituted... [Pg.1102]

Recently, an example of intramolecular formation of Ar-Ar bonds has been reported, consisting in the preparation of dibenzopyranone derivatives by a highly selective, Pdfacacf /CuCl-mediated tandem reaction [70]. Substituted 2-nitrobenzoic acids and methyl 2-bromo benzoate derivatives are used as starting materials. [Pg.636]

In 2013, Shi and coworkers described the first example of phenolic hydroxy group-directed C-H carbonylation to prepare lactones (Scheme 3.25) [50]. Using 5mol% Pd(OAc)2, 10mol% Cu(OAc)2, 2equiv. of Na2C03, and O.Sequiv. of PivOH, dibenzopyranones could be synthesized from 2-arylphenols under an atmospheric pressure of CO and air. The reaction is of wide substrate scope, whereas the steric hindrance and electronic character of phenolic aromatic ring are critical to the yield. [Pg.78]


See other pages where Dibenzopyranones is mentioned: [Pg.515]    [Pg.516]    [Pg.54]    [Pg.382]    [Pg.61]    [Pg.1501]    [Pg.166]    [Pg.166]    [Pg.538]    [Pg.644]    [Pg.215]    [Pg.215]    [Pg.93]    [Pg.253]   
See also in sourсe #XX -- [ Pg.353 ]




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Dibenzopyranone formation

Stereoselective Preparation of Hexahydro dibenzopyranones and intermediates therefor

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