Chemoselective Knoevenagel reaction as a novel route for the synthesis of biscoumarinyl methylsulphones and 4+1, 1+4 approach synthesis of aminooxadiazolyl and N-(2,5-dimethyl)pyrrolylcoumarins

258-2664-Bromomethylcoumarins 1 on reaction with thiourea gives 4-mercaptomethyl coumarins 2, which on further reaction with ethyl chloroacetate afford the corresponding sulphide esters 3a-c. The sulphone esters 3d-f which are obtained upon oxidation of compounds 3a-c, undergo cyclisation with salals through Knoevenagel reaction to furnish biscoumarins 4 in good yield. Also esters 3a-f on reaction with hydrazine hydrate (99.9%) give the corresponding carbohydrazides 5. Compounds 5 when reacted separately with cyanogen bromide and acetonyl acetone yield aminooxadiazolyl 6 and N-(2,5-dimethyl)pyrrolylcoumarins 7, respectively. The compounds have been characterized by elemental analysis, IR, 1H NMR, mass and 2D-HOMO COSY data. All the newly synthesized compounds have been screened for antimicrobial activity against gram-ve bacterium Escherishia coli, gram+ve bacterium Bacillus staphylococci and fungi penicillium and Aspergillus

Synthetic and Structural Studies on Novel 4,3′-Bicoumarins

<div><p></p><p>A series of directly linked 4-3′ bicoumarins have been synthesized by both Knoevenagel and Perkin reactions. This single-step transformation was accomplished by the reaction of coumarin-4-acetates with substituted salicylaldehydes in presence of piperidine using ethanol as solvent and by the reaction of coumarin-4-acetic acids with substituted salicylaldehydes in the presence of sodium hydride in acetic anhydride. Greater yields have been obtained in the sodium hydride and acetic anhydride condition. An intermediate chalcone with an <i>ortho</i>-hydroxyl group, which is a precursor for lactone formation, has been isolated and its structure has been confirmed by x-ray analysis. The nonplanar S-<i>cis</i> arrangement of two C4-C3’ double bonds has been confirmed by nuclear Overhauser spectroscopy (NOE) and x-ray studies. The UV-fluorescence studies support the formation of a conjugated bicoumarin system.</p></div