That the key step in the title reaction is 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).

C K GHOSH

A BHATTACHARYYA

C BANDYOPADHYAY

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

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

Journal of the Chemical Society, Chemical Communications

Dienamine 1 with W-phenylmaleimide and chromenone 14 as well as 15 produces, through initial [4 + 2]cycloaddition, xanthenones 10 and 18, respectively. Initial Michael addition of 1 to chromenones 14 and 16, and dimethyl acetylenedicarboxylate (DMAD), triggers the formation of xanthenone 19, 4-azaxanthenone 26 and substituted fumarate 49, respectively. Initial [2 + 2]cycloadducts of dienamines 1-3 with electrophilic acetylenes always undergo further transformations. Thus, 1 with DMAD, dibenzoylacetylene and ethyl propiolate (EP) ultimately gives xanthenones 33, 34 and 37, respectively, the latter being admixed with flavone 43. Enamine 2, cyclisable to xanthenone 11, gives 33 and 35 with DMAD, and 37 and 44 with EP. Reaction of 3 with DMAD affords 36 exclusively. © The Royal Society of Chemistry 1999.

Journal of the Chemical Society - Perkin Transactions 1

Benzopyrans. Part 41.1 Reactions of 2-(2-dimethylaminovinyl)-lbenzopyran-4-ones with various dienophiles

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.

Unusual condensation of 2-(2-dimethylaminovinyl)-1-benzopyran-4-one with dimethyl acetylenedicarboxylate: Formation of 2,3-bis(methoxycarbonyl)xanthen-9-one

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-POCl3 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-Ac2O, affords the xanthone 13 by refluxing with NaOMe in MeOH. © 1993.

Journal	Journal of the Chemical Society, Chemical Communications
Publisher	-
ISSN	0022-4936