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Glycolaldehyde is a biomass-derived chemical compound available from cellulose or glucose. Until now, little attention has been devoted to its use towards value-added chemicals. To explore novel transformations of glycolaldehyde, in this work, a three-component reaction of glycolaldehyde, indole and a 1,3-dicarbonyl compound was developed to synthesize a class of 3-(indol-3-yl)-2,3-dihydrofurans. Using glycolaldehyde diethyl acetal as a glycolaldehyde source, the reaction can be performed in organic solvents, and two catalytic systems were proved to be effective: (a) Sc(OTf)3/nitromethane and (b) Ni(ClO4)2·6H2O/acetonitrile. However, these conditions applied to the direct use of the bio-based glycolaldehyde aqueous solution did not provide the dihydrofurans efficiently. To enable the use of an aqueous solution of glycolaldehyde, a hitherto unreported deep eutectic solvent (DES) was developed by using FeCl3·6H2O and meglumine (N-methylglucamine) as precursors. The FeCl3·6H2O/meglumine DES was characterized by FTIR, TGA and DSC, and the obtained results demonstrated unambiguously the formation of a DES. This DES was found to be an efficient and water-compatible promoting medium for the abovementioned three-component reaction. A variety of 3-(indol-3-yl)-2,3-dihydrofurans were synthesized in good yields. The FeCl3·6H2O/meglumine DES system can also be recycled without significant loss of activity. [ABSTRACT FROM AUTHOR]

2-Alkoxy-2,3-dihydrofurans were found to be versatile benzannulation reagents. Indoles can be synthesized in good to excellent yields via the [4+2] annulation of 2-butoxy-2,3-dihydrofuran with pyrroles catalyzed by copper bromide. With the same protocol, carbazoles can also be obtained when indoles are used as starting material with the aid of p-toluenesulfonic acid. This type of benzannulation reagent can also be used to synthesize benzofuran, benzothiophene and naphthalene derivatives in the presence of a catalytic amount of triflic acid in moderate yields. This benzannulation protocol features wide substrate scope and mild reaction condition. Moreover, most of examples have a good regioslectivity. [ABSTRACT FROM AUTHOR]

An effective method to synthesize α-functionalized furan and pyrrole derivatives was developed using 2-alkoxy-2,3-dihydrofurans as modular precursors. This protocol featured a previously unreported tandem nucleophilic substitution/heteroaromatization reaction. Nucleophiles such as indole, α-oxoketene dithioacetal, trimethoxybenzene, and dimethoxynaphthalene can react readily with 2-alkoxy-2,3-dihydrofurans to afford α-functionalized five-membered ring heterocycles in the presence of acid catalysts, such as copper bromide and iron chloride. The mechanism of the reaction was also discussed, in which the first step, nucleophilic substitution, is the key in triggering the succeeding heteroaromatization. This method can also be extended to the synthesis of dihydrothiophenes. [ABSTRACT FROM AUTHOR]

A series of substituted title furans is treated with pyrroles or indoles under catalytic conditions to produce indole or carbazole derivatives, respectively. [ABSTRACT FROM AUTHOR]

The front cover picture, provided by Yanlong Gu and co ‐ workers, describes a class of versatile benzannulation reagents, 2 ‐ alkoxy ‐ 2,3 ‐ dihydrofurans that can be obtained from readily available substrates through a simple synthetic operation. Indoles, carbazoles, naphthalenes, benzofurans, and benzothiophenes can be synthesized via the [4+2] annulation of 2 ‐ butoxy ‐ 2,3 ‐ dihydrofuran with various electron ‐ rich heterocycles or arenes in the presence of Lewis acid or Brønsted acid catalysts. Details can be found in the communication on pages 2260 – 2266 (C. Liu, W. Huang, M. Wang, B. Pan, Y. Gu, Adv. Synth. Catal.­ 2016, 358, 2260 – 2266; DOI: 10.1002/adsc.201600185). [ABSTRACT FROM AUTHOR]

2-Butoxy-substituted-2,3-dihydrofurans and a variety of carbon nucleophiles offer a diverse synthesis of furans, pyrroles, and dihydrothiophenes in the presence of a Cu- or Fe-catalyst. [ABSTRACT FROM AUTHOR]