Rapid and Efficient Synthesis of Some Isatin DerivativesBased on Novel Heterocycles Containing OxadiazoleMoiety

The focus of the scheme is the Microwave-Assisted Organic Synthesis (MAOS) of 5 mercapto-2-[5-substitutcd-3-(4-arylimino)-1 methyl-indol-2-one]-I, 3. 4-oxadiazolc(4a -g) analogs and the comparison of this method with the conventional one.In the present work, condensation of appropriate indol-2,3-diones with halogensubstituted anilincs under microwave irradiation at a power level of 140 watts yields 5 substituted-3-(4-arylimino)-indol-2-one (la-g). In the next step, 1a-g on treatment with ethyl chloroacctatc in anhydrous K2C03 and dry acetone furnished [5-substituted3-(4-arylimino)-2-oxo]-I-indole-ethylacetate (2a-g) which on reaction with hydrazine hydrate in methanol gave [5-substitutecl-3-(4-arylimino)-2-oxol-l-indolcaeetylhydrazidc (3a-g). In the last step, a solution of compounds (3a-g) in ethanolicKOB on treatment with CSz gave title compounds 5-mercapto-2-[5-substituted-3-( 4arylimino)-I methyl-indol-2-one]-I, 3, 4-oxadiazolc (4a-g) under microwaveirradiation at a power of 140 watts. MW irradiation led to higher yields in much lesstime than that by conventional methods.