Water Extract of Lemon (WEL) as a Promoter: Green and Regioselective Synthesis of Alkyl‐4‐(1H‐indol‐3 yl)‐2‐alkyl‐4H‐chromene‐3‐carboxylates Using 4H‐chromenes and Indoles

Abstract

An efficient, simple, green, regioselective and catalyst-free synthesis of alkyl-4-(1H-indol-3yl)-2-alkyl-4H-chromene-3-carboxylates is disclosed by employing indoles and substituted chromene derivatives under mild reaction condition. This is a novel green methodology, simple, eco-friendly and easy to operate. Biomass-derived catalyst Water Extract of Lemon (WEL) was used as a promoter for this procedure. The methodology could be applicable for cost-effective large scale production of alkyl-4-(1H-indol-3yl)-2-alkyl-4H-chromene-3-carboxylates in good to excellent yield.

Advancements in the Preparation of 4H‐Chromenes: An Overview

“…Previously, Zhu, [10] Lenin, [13] and Mechram [22] have independently reported the utilization of the strategy of nucleophilic addition to 1‐benzopyrylium ion for the synthesis of 4‐indolyl 4 H ‐chromenes using substituted indoles as nucleophiles. Compared to these reports, Yin and She in 2012 employed the tandem Michael addition/cyclization/dehydration strategy, and also successfully realized the preparation of such compounds from 2‐hydroxychalcones 54 and substituted indoles 27 [36a] .…”

“…Recently, Lenin and co-workers also studied the similar reaction, and disclosed an efficient, simple, green, regioselective and catalyst-free synthesis of 4indolyl 4H-chromenes from substituted indoles 32 and 2H-chromene hemiketals 43 by employing water extract of Lemon (WEL) as a biomass-derived catalyst. [13] The author tested most common substrates and found WEL could promote the formation of desired products 44 in good to high yields at room temperature for 2-6 h (Scheme 10). This reaction also proceeded exclusively with a complete C4-regioselec- tivity, which possibly originated from the conjugation effect between the C4 position and the ester group of C3 position.…”

Ethylenediamine Functionalized Cellulose Acetate [CAEDA] Nanosized Solid Base Catalyst in the Synthesis of 2‐Amino‐4H‐Chromenes and 5‐Substituted‐1H‐Tetrazoles

“…substituted 2-amino-4H-chromenes. [39][40][41][42][43][44][45][46][47][48][49][50][51][52] Very recent work has been done to synthesize Alkyl-4-(1H-indol-3 yl)-2-alkyl-4H-chromene-3-carboxylates using water extract of lemon [107] and is still in process but many of the protocols suffer from certain drawbacks such as tedious work-up, long reaction time, harsh reaction conditions etc. So, we present here the synthesis of 2amino-4H-chromenes using dimedone, different substituted aromatic aldehydes and malononitrile using ethanol as a solvent at 80°C in presence of Cellulose acetate [1,2-ethylenediamine][CAEDA] as a catalyst (Scheme 1).…”