3-Benzylbenzothiazolylidene Carbene Catalyzed Isomerization of Dimethyl Maleate to Dimethyl Fumarate: Experimental and Theoretical Results

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Author(s): Minita Ojha, Shweta Choudhary, Raj K. Bansal.

Journal Name: Current Organocatalysis

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Background: N-Heterocyclic carbenes (NHCs) have emerged as ubiquitous species having applications in a broad range of fields, including organocatalysis and organometallic chemistry. Since Arduengo and co-workers first isolated a bottlable NHC, namely imidazol-2-ylidene derivative, these nucleophilic species have attained a prominent place in synthetic organic chemistry. The NHC-induced non-asymmetric catalysis has turned out to be a really fruitful area of research in recent years.

Methods and Results: The isomerization of dimethyl maleate to dimethyl fumarate catalyzed by an N-heterocyclic carbene (NHC), namely 3-benzylbenzothiazolylidene has been investigated experimentally and theoretically. Dimethyl maleate on reacting with 3-benzylbenzothiazolylidene carbene (10 mol%), generated in situ from the reaction of 3-benzylbenzothiazolium bromide with triethylamine in diethyl ether at room temperature under nitrogen atmosphere isomerizes quantitatively to dimethyl fumarate. Theoretical investigation of a model reaction scheme at the DFT level reveals that initial attack of the carbene, which is the rate-determining step, is followed by rotation about the C-C bond in preference to a higher energy path involving proton abstraction. The species so formed splits off the carbene to yield dimethyl fumarate.

Conclusions and Perspective: 3-Benzylbenzothiazolylidene carbene catalyzes isomerization of dimethyl maleate to its trans-isomer. This carbene can be used in other catalytic reactions, such as acyloin condensation and Stetter reaction.

Keywords: Nitrogen heterocyclic carbene; organocatalysis; isomerization; dimethyl maleate; DFT calculations.

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(E-pub Ahead of Print)
DOI: 10.2174/2213337206666191018111354