Phase Transfer Catalysis Assisted Thorpe Reaction for the Synthesis of 3-Aminothiophene-2-carboxylates

R D Shah

doi:10.1155/2011/650501

Abstract

Thorpe cyclization constructing synthetically important methyl or ethyl 3-amino-4-arylthiophene-2-carboxylates has been studied using eco friendly phase transfer catalysis technique. 3-Amino-4-arylthiophene-2-carboxylates have been synthesized from 3-hydroxy-2-arylacrylonitriles and thioglycolates under different solid-liquid phase-transfer conditions.

Highlights

In the chemistry of five member amino heterocycles the intermolecular Thorpe[1,2,3] reaction and its intramolecular version Thorpe-Zeigler[4,5,6] reactions are one of the most promising lines
Strategy to incorporate Thorpe reaction with eco friendly[15,20] phase-transfer catalysis (PTC) technique is always been of great interest to study
For liquid-liquid phase-transfer conditions CH2Cl2 / KOH, low or lack of reactivity was observed in the presence of catalysts such as tetrabutylammonium bromide (TBAB) and triethylbenzyl- ammonium chloride (TEBA), results showed concomitant decomposition of both reactants after prolonged reaction time and even under heating conditions (24 h, 60-70 OC)

Summary

Introduction

In the chemistry of five member amino heterocycles the intermolecular Thorpe[1,2,3] reaction and its intramolecular version Thorpe-Zeigler[4,5,6] reactions are one of the most promising lines They are base catalyzed and sodium or potassium alkoxide[7,8], sodium hydride[9], potassium hydroxide[10], lithium hydroxide[11] and potassium carbonate[1,2] were employed frequently. We report synthesis of important building blocks such as 4-substituted methyl or ethyl 3-amino-4arylthiophene-2-carboxylates involving Thorpe reaction from 3-hydroxy-2-aryl acrylonitriles[19] and thioglycolates under different solid-liquid PTC. 6 was choice of catalyst, where as acetonitrile was used as solvent (Scheme 1)

H S COOR1

Results and Discussion

Conclusions