Synergistic effect of natural chickpea leaf exudates acids in heterocyclization: a greener protocol for benzopyran synthesis.

Shashikant Damte,Snehali Mali,Sachin Shinde,Suresh Patil

doi:10.1098/rsos.170333

Abstract

Without using any toxic or hazardous reagent, ligand, acid, transition metal catalyst, additives/promoters and organic solvent, green Knoevenagel condensation and tandem Knoevenagel–Michael reactions have been successfully carried out by using chickpea leaf exudates as a naturally sourced Bronsted acid type bio-catalyst. The reaction proceeds in neat chickpea leaf exudates at room temperature in aqueous conditions in very short reaction times, and therefore, it is an evergreen and environmentally sound alternative to the existing protocols for benzopyran synthesis. In comparison to the conventional methods, this synthetic pathway complies with several key requirements of green chemistry principles such as the utilization of biodegradable catalyst obtained from renewable feedstock, auxiliary aqueous conditions, along with waste prevention. The same protocol was also extended to the synthesis of 2H-xanthene-1,8-diones by condensation of aromatic aldehydes with dimedone achieving excellent yields. Thus, the reported protocol offers an attractive option because of its ecological safety, environmental acceptance, sustainability, low-cost straightforward work-up procedure and with excellent values of green chemistry metrics as compared with other reported methods.

Highlights

While considering the increasing environmental pollution and its intensive impact on living systems, developing chemical processes using more environmentally acceptable chemicals, catalysts, solvents, atom-efficient methods and energy-efficient2018 The Authors
The reason is that the organic transformations employ higher consumption of solvents than the reagents and the employed solvents are difficult to recycle [3]; for the process to be in line with the green chemistry principles, the first task is to replace the toxic catalysts and hazardous organic solvents with green ones
Considering the significance of naturally sourced catalysts, in this work, we explore the catalytic activity of chickpea leaf exudates (CLE) as natural green acidic medium in the synthesis of benzopyranes starting from readily available dimedone and salicylaldehydes in presence of aqueous medium and at ambient temperature

Summary

Introduction

While considering the increasing environmental pollution and its intensive impact on living systems, developing chemical processes using more environmentally acceptable chemicals, catalysts, solvents, atom-efficient methods and energy-efficient2018 The Authors. Biosynthetic processes involving bio-based solvents or catalysts such as Cyrene [8,9], glucose [10], dihydrolevoglucosenone (Cyrene) [11] and agro-waste based solvents or catalysts like metal based [12,13], Kolakhar [14], WEB [15,16,17], H2O2 in WERSA [18], water extract of papaya bark [19], have received much attention as a viable alternative for the development of green protocols for organic transformations [20,21,22,23,24,25]

Objectives

Methods

Results

Conclusion