PEG 400

Introduction

Polyethylene glycol 400 (PEG 400) is a water-soluble and hygroscopic polymer with a molecular weight of 400 Da.[ ¹ ] At room temperature it exists as colorless viscous liquid. Reactions promoted by PEG 400 have attracted attention due to their ease of workup and inexpensive and eco-friendly nature. It can also act as phase-transfer catalyst.

Till date reactions involving PEG 400 have been carried out and investigated, for example, Heck reaction,[ ² ] Lindlar catalytic hydrogenation,[ ³ ] asymmetric dihydroxylation,[ ⁴ ] Baylis–Hillman reaction,[ ⁵ ] Biginelli reaction,[ ⁶ ] Suzuki–Miyaura coupling,[ ⁷ ] Stille cross-coupling,[ ⁸ ] Wacker reaction,[ ⁹ ] asymmetric aldol reaction,[ ¹⁰ ] 3,4-dihydropyrim­idones via Biginelli reaction,[ ¹¹ ] Strecker reaction,[ ¹² ] etc.

Abstracts

(A) Kouznetsov et al. had developed a simple and efficient one-pot method for the synthesis of novel 2,4-diaryl-1,2,3,4-tetrahydroquinolines using a three-component imino Diels–Alder cycloaddition ­between trans-isoeugenol or trans-anethole, anilines, and benzaldehyde in the presence of BF3·OEt2 in PEG 400.[ 13 ]
(B) Jorapur et al. reported the synthesis of dibenz[b,f]-1,4-oxazepine via intramolecular cyclization and revealed the utility PEG 400 as recyclable reaction medium.[ 14 ]
(C) Guchhait and Madaan reported the Ugi-type multicomponent ­reaction of heterocyclic amidines with aldehydes and isocyanides catalyzed by zirconium(IV) chloride in PEG 400. This protocol offers the rapid, environmentally friendly and regioselective synthesis of medicinally important N-fused 2- and 3-aminoimidazoles in good to high yields.[ 15 ]
(D) Reddy et al. developed a synthetic route to afford styrylfurans in good yields via 1,3-dipolar cycloaddition between isocyanides, dialkyl acetylenedicarboxylates, and α,β-unsaturated aldehydes in PEG 400.[ 16 ]
(E) Shitole et al. reported the synthesis of 2-amino-4H-chromenes by condensation of aromatic aldehyde, malononitrile, and α-naphthol.[ 17 ]
(F) Zhang et al. disclosed the role of PEG 400 as an efficient catalyst to synthesize quinaoxalines via condensation of 1,2-diamines with 1,2-dicarbonyl compounds in excellent yields under mild reaction conditions.[ 18 ]
(G) Liang et al. reported a metal-free synthesis of amides by direct oxidative amidation of aldehydes with amines in a PEG 400/oxidant system in good to excellent yields.[ 19 ]
(H) Wang et al. reported a Hantzsch 1,4-dihydropyridines synthesis via a one-pot condensation of aldehydes, β-dicarbonyl compounds, and ammonium acetate in PEG 400. This method has the advantages of good yields, less pollution, and simple reaction conditions.[ 20 ]
(I) Bhosle et al. reported an efficient one-pot three-component cyclocondensation of 4-(p-tolyl sulfonoxy) benzaldehyde, aryl amines, and mercaptoacetic acid in PEG 400 to yield 2,3-disubstituted 4-thiazolidinones.[ 21 ]
(J) Karnakar et al. developed a simple, efficient and eco-friendly synthetic protocol for the synthesis of pyrazolo[3,4-b]quinolines via a one-pot three-component reaction of aldehydes, amino pyrazole, and 1,3-cyclohexanediones using recyclable PEG 400 as reaction medium.[ 22 ]

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