Showing papers by "Chandra Kanta Ghosh published in 1999"
TL;DR: In this paper, the authors showed that cycloadducts of dienamines with electrophilic acetylenes always undergo further transformations, resulting in the formation of xanthenone and substituted fumarate.
Abstract: Dienamine 1 with N-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
22 citations
Journal Article•
TL;DR: The surface of alumina is polar and contains immobile catalytic Bronsted and Lewis acid as well as base sites; the composition and nature of these sites can be altered by heating, and hydroxy groups on oxide surfaces are much weaker nucleophiles than the lattice oxide anions as mentioned in this paper.
Abstract: The surface of alumina is polar and contains immobile catalytic Bronsted and Lewis acid as well as base sites; the composition and nature of these sites can be altered by heating, and hydroxy groups on oxide surfaces are much weaker nucleophiles than the lattice oxide anions}. That is why alumina not only functions as a solid support for interacting reagents but also mediates several types of reactions e.g. Cannizzaro reaction. , Meerwein-Pondorf-Verley type reduction 7 including internal redox reaction of some ketols, epimerisation, Favorskii rearrange10 I . II . 12 I 11 ment, acy om , OXlrane, cyc opropylketone . rearrangements, skeletal rearrangement of quadri cyclanone l4 , spifting of ethylenic linkages l5 , selfcondensation of methylene aldehydes, methylene ketones l 6 and 3-acetylchromone I7 , deacetalisation and subsequent deformylation 18 and conversion of benzyl halide to dibenzyl ether l9 . Alumina mediated reactions of chloroacetone with 4-oxo-4H-I-benzopyran3-carbaldehyde, -3-c.arbonitrile and -3-carboxylate give the products different from those . ari sing from the respective reactions conducted ' in acetone containing anhydrous potassium carbonate The transformation of the title 4-oxo-4H-I-benzopyran (chromone) derivati ves 1-4, each containing three electropositive centres (namely C-2, formylor
3 citations
2 citations