Falguni Chattopadhyay

Novel formation of 6-acyl-5-(2-pyrrolyl)-3H-pyrrolizines by base-catalysed condensation of pyrrole-2-aldehyde with methyl ketones

Abstract Pyrrole-2-aldehyde undergoes condensation with methyl ketones in aqueous ethanolic alkali in a 2:1 mole ratio yielding 6-acyl-5-(2-pyrrolyl)-3 H -pyrrolizines as novel products in moderate yield.

Novel conversion of 3-(α-hydroxybenzyl)flavones to 3-benzoylchromones and 3-cyanoflavones with NaN3/TFA

Abstract On treatment with NaN 3 /TFA, 3-(α-hydroxybenzyl)flavones are converted to 3-benzoyl- chromones and 3-cyanoflavones, plausible mechanisms for which have been suggested.

Simple Diastereoselective Synthesis of (2S*,2′R*,3′R*,4S*)-2,3′-Diphenylspiro[chroman-3,2′-oxiran]-4-ols and (2S*,2′S*,3′S*,4S*)-2,3′-Diphenylspiro[chroman-3,2′-oxiran]-4-ols

Oxiranes (epoxides) are very versatile building blocks in organic synthesis, and they can be opened up with a wide range of nucleophiles. Nucleophilic addition to epoxides plays a pivotal role in the stereoselective preparation of 1,2-difunctional compounds. It has been one of the most thoroughly studied reactions of epoxides, and for this different promoters and conditions have been developed. 1,3-Disubstituted and 1,2,3-trisubstituted 2,3-epoxyalcohols belong to an important group of epoxy compounds, as opening of their epoxy ring can lead to interesting compounds having three contiguous stereogenic centers. This fascinating aspect is the key factor for their use as precursors for the synthesis of a wide range of important and useful organic molecules. Two main routes for synthesis of 2,3-epoxyalcohols are i) epoxidation of allyl alcohols, and ii) chemoselective ketone reduction of a,b-epoxyketones. Both allyl alcohols and a,b-epoxyketones are readily available compounds, and those belonging to the latter type are generally prepared by a very simple reaction, viz., epoxidation of a,b-unsaturated ketones with hydrogen peroxide and alkali. It is worthwhile to mention here that for the reduction of a,b-epoxyketones, along with the chemoselectivity, the stereoselectivity of the reactions plays a very important role in the transformation steps necessary for achieving the targeted synthesis. This has led to the development of a good number of methods for chemoselective and stereoselective reduction of a,b-epoxyketones. E-3-Benzylideneflavanones (1) prefer a conformation in which the 2-aryl group is axially oriented. Sodium borohydride reduction of 1, studied in our laboratory, was

Novel formation of spirocyclic oxazolines in the reaction of some (E)3-(4-methoxybenzylidene)flavanones with NaN3/c.H2SO4-HOAc

On treatment with NaN3/c.H2SO4-HOAc, some (E)-3-(4-methoxybenzylidene) flavanones yield a new type of flavonoid-derived spirocyclic oxazolines in moderate yield. A plausible mechanism for formation of these products is suggested.

Synthesis of (4S*,5S*)-diphenyl-1,3,4,5-tetrahydro-2H-[1]benzopyrano [4,3-d]pyrimidine-2-thiones by base-catalysed cyclocondensation of (E)-3-benzylideneflavanones with thiourea, and determination of their monoacetylation site

Base-catalysed cyclocondensation of (E)-3-benzylideneflavanones with thiourea has been found to be highly stereoselective, producing (4S*,5S*)-diphenyl-1,3,4,5-tetrahydro-2H-[1]benzopyrano[4,3-d]pyrimidine-2-thiones in high yield, the structure of one of which has been determined by X-ray crystallography. Just like 4,6-diaryl-3, 4-dihydropyrimidine-2(1H)-thiones, the said products also undergo monoacetylation on treatment with Ac2O. The site of acetylation in both of these classes of compound are established by detailed NMR spectral studies.