Chandra Kanta Ghosh

Benzopyrans. Part 30. Synthesis of substituted xanthones from 3-acyl-2-methyl-1-benzopyran-4-ones

Abstract The xanthone 8 results from the base catalysed self-condensation of the chromone 1 . The chromone 2 gives the xanthones 9 and 11 with sodium and DMF-POCl 3 respectively, phenol 14 with NaOMe, and the pyran 22 with 2-thiomethylchromone 6 . The enamine 16 on Vilsmeier-Haak reaction affords the chloroxanthone 12 . The pyran 15 , isolated as a byproduct from the reaction of ω-acetyl-2-hydroxyacetophenone with HC(OEt) 3 -Ac 2 O, affords the xanthone 13 by refluxing with NaOMe in MeOH.

Heterocycles fused with the 2,3-bond of [1]benzopyran

Article de synthese couvrant la litterature correspondant au volume 103 des Chemical Abstracts

Benzopyrans - XXXIII. [4+2]Cycloaddition of N,N-dimethylhydrazones and anils of 2-unsubstituted and 2-methyl-4-oxo-4H-1-benzopyran-3-carboxaldehyde with N-phenylmaleimide

Abstract The chromone derivatives 1, 2 , and 4 give with N -phenylmaleimide the cycloadducts 5 , 12 , and 13 which are converted by palladised charcoal into 2-azaxanthone 6 , xanthones 14 and 15 , respectively. Treatment of the azaxanthone 5 with acidic ethanol produces a mixture of salicyloylpyridines 7–9 .

Base catalysed deacylative dimerisation of 3-acetylchromenone: a facile Diels–Alder reaction

That the key step in the title reaction id the Diels–Alder addition of 3-acetylchromenone (1) to its acyl–acyl rearranged isomer (9′a) is supported by the formation of 2-salicyloylxanthone (5) from the reaction of (9) with any of the chromenones (1)—(4)

Benzopyrans. 31. Reaction of 1,1-diacetyl-2-(6-methyl-4-oxo-4H-1-benzopyran-3-yl)ethylene with phenyldiazomethane☆

Abstract Phenyldiazomethane yields with the title alkene 1 a mixture of the trans -cyclopropane 6 , benzopyran 8 , pyrazole 9 , and cis -dihydrofuran 12 . The cyclopropane 6 thermally rearranges to a trans -dihydrofuran tentatively assigned the structure 4 .

Benzopyrans. Part 44. Synthesis of 3-(4-Oxo-4H-1-benzopyran-2-yl)indolizines

The pyridinium methylid (5), generated from 1-(4-oxo-4H-1-benzopyran-2-yl)methylpyridinium iodide (4) in the presence of a base, undergoes [3+2] cycloaddition with dimethyl acetylenedicarboxylate and ethyl propiolate, thecycloadducts rapidly aromatising to the indolizines (8) and (9), respectively. Similar cycloaddition of 5 with ethyl acrylate and acrylonitrile is also followed by dehydrogenation giving respectively the indolizines (9) and (10).

UNUSUAL CONDENSATION OF 2-(2-DIMETHYLAMINOVINYL)-1-BENZOPYRAN-4-ONE WITH DIMETHYL ACETYLENEDICARBOXYLATE: FORMATION OF 2,3-BIS(METHOXYCARBONYL)XANTHEN -9-ONE

Reaction of dienamine 2 (R = H and Me) with N -phenylmaleimide or chromone 3 gives xanthones 5 and 8, respectively, through initial [4 + 2] cycloaddition, whereas reaction with dimethyl acetylenedicarboxylate affords xanthone 13.

Benzopyrans. Part 43. Reactions of some simple condensates of 4-oxo-4H-1-benzopyran-3-carboxaldehyde with ethyl β-aminocrotonate

With ethyl β-aminocrotonate, the chromone 2A (X = H(A), Me(B), Cl(C)) gives a mixture of the dihydropyridine 4A and pyranopyridine 15A, 2B gives 4B, and 2C gives varying amounts of the substituted enamine 3C, pyridone 4C and benzophenone 8. 5-Hydroxy-5H-[1]benzopyrano-[4,3-b]pyridine 11 (< 3%) was obtained in each case. Palladised charcoal dehydrogenates dihydropyridines 4A and 4B to respectively 12A and 12B and ammonia converts 12A into the diazanaphthalene 13.

Benzopyrans. Part 38.1 Reactions of 4-Oxo-4H-1-benzopyran-3-carbaldehyde, -3-carbonitrile and -3-carboxylate with Chloroacetone and a Note on the Stereochemistry of Benzo[b]cyclopropa[e]pyrans

The title benzopyranones 1–3 give the benzo[b]furan 7 and the benzo[b]cyclopropa[e]pyrans 8 and 9 with chloroacetone in acetone containing anhydrous potassium carbonate and a catalytic amount of potassium iodide but give the 1-benzopyranones 10, 11 and 14 in dichloromethane in the presence of Brockman neutral alumina, respectively.

Benzopyrans. Part 23. Nitrogen heterocycles fused with or linked to 1-benzopyran from 3-acyl-2-methyl-1-benzopyran-4-one

The enamine (2), prepared from the title benzopyranone (1; R2= H, Me, and Ph) and dimethylformamide dimethyl acetal, on treatment with ammonia and hydroxylamine gives the fused pyridine (5) and pyridine 2-oxide (10), respectively. Hydrazine, phenylhydrazine, and guanidine undergo initial 1,6-addition to the enamine (2) ultimately giving the pyrazoles (14) and (15), and the pyrimidine (17), respectively. The pyridinioacetamidate (11), prepared from the enamine (2; R2= Me and Ph) and acetohydrazide, thermolyses to the fused pyridine (5). A refluxing ethanolic solution of the enamine (2; R2= Me and Ph) with ethyl glycinate forms the ester (18) which on treatment with ethanolic sodium ethoxide produces the azepine (20).