Abstract
An environmentally benign, efficient and facile route is developed for the synthesis of novel spiro[indoline-3,2'-thiazolo[5,4-e]pyrimido[1,2-a]pyrimidine] derivatives. The benzylidene derivatives of spiro[indoline-thiazolidinones] 6 containing an α,β-unsaturated ketonic function [CH=CH-CO-] have been used as a component of Michael addition with an equimolar amount of 2-aminopyrimidine 7 to give a series of novel spiroindole derivatives 9 in a single step using montmorillonite KSF as inorganic solid support with few drops of DMF. In comparison to conventional synthesis involving tedious multistep procedures, the present method indicates operational simplicity, shorter reaction time and higher yields which can prove this procedure as a useful alternative for the synthesis of novel spiro heterocycles.
Highlights
Heterocyclic scaffolds represent the central framework of many biologically active compounds
As part of our ongoing program to develop efficient and robust methods for the preparation of biologically relevant compounds[24] from readily available building blocks, which are novel yet resemble known biologically active molecules by virtue of the presence of some critical structural features, we have developed a facile, efficient, one-pot method for the synthesis of novel spiro[indoline-3,2'-thiazolo[5,4-e]pyrimido[1,2a]pyrimidin]-2(1H)-one 9a-d by the reaction of 5'-benzylidene-3'-phenylspiro[indoline-3,2'thiazolidine]-2,4'(1H)-dione 6a-d with 2-aminopyrimidine 7 using montmorillonite KSF with few drops of DMF under microwave irradiation and its comparison with synthesis under conventional conditions, which involves multistep tedious procedure requiring excessive use of solvent and extra labor for separation and purification of compounds as various steps
The spiro[indoline-thiazolidinones] system has been synthesized earlier conventionally by a two step procedure in 40–60% yield using isatin-3-imines as key intermediate, which were synthesized from substituted isatins and aromatic amines
Summary
Heterocyclic scaffolds represent the central framework of many biologically active compounds. As part of our ongoing program to develop efficient and robust methods for the preparation of biologically relevant compounds[24] from readily available building blocks, which are novel yet resemble known biologically active molecules by virtue of the presence of some critical structural features, we have developed a facile, efficient, one-pot method for the synthesis of novel spiro[indoline-3,2'-thiazolo[5,4-e]pyrimido[1,2a]pyrimidin]-2(1H)-one 9a-d by the reaction of 5'-benzylidene-3'-phenylspiro[indoline-3,2'thiazolidine]-2,4'(1H)-dione 6a-d with 2-aminopyrimidine 7 using montmorillonite KSF with few drops of DMF under microwave irradiation (scheme-1) and its comparison with synthesis under conventional conditions, which involves multistep tedious procedure requiring excessive use of solvent and extra labor for separation and purification of compounds as various steps. The results showed that the combination of clay with DMF is most suitable reaction medium for present investigation involving the annulation of pyrimidine ring on 5'-benzylidene-3'-phenylspiro[indoline-3,2'thiazolidine]-2,4'(1H)-dione 6 in single step.
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