Anionic N-heterocyclic carbenes by decarboxylation of sydnone-4-carboxylates

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Luecke , A-L , Wiechmann , S , Freese , T , Nieger , M , Foeldes , T , Papai , I , Gjikaj , M , Adam , A & Schmidt , A 2018 , ' Anionic N-heterocyclic carbenes by decarboxylation of sydnone-4-carboxylates ' , Tetrahedron , vol. 74 , no. 16 , pp. 2092-2099 . https://doi.org/10.1016/j.tet.2018.03.019

Title: Anionic N-heterocyclic carbenes by decarboxylation of sydnone-4-carboxylates
Author: Luecke, Ana-Luiza; Wiechmann, Sascha; Freese, Tyll; Nieger, Martin; Foeldes, Tamas; Papai, Imre; Gjikaj, Mimoza; Adam, Arnold; Schmidt, Andreas
Contributor: University of Helsinki, Department of Chemistry
Date: 2018-04-19
Language: eng
Number of pages: 8
Belongs to series: Tetrahedron
ISSN: 0040-4020
URI: http://hdl.handle.net/10138/314177
Abstract: Unstable N-heterocyclic carbenes can be masked and stabilized as pseudo-cross-conjugated hetarenium-carboxylates which decarboxylate on warming. This study deals with the decarboxylation of carboxylates of mesoionic compounds to generate anionic N-heterocyclic carbenes. Lithium sydnone-4-carboxylates were therefore prepared via 4-bromosydnones by halogen-lithium exchange with nBuLi and subsequent treatment with carbon dioxide. Protonation gave the corresponding sydnone-4-carboxylic acids. Thermogravimetric measurements in addition to temperature dependent IR spectroscopy proved the decarboxylation of lithium sydnone-4-carboxylates and formation of the corresponding sydnone anions which can be represented as anionic N-heterocyclic carbenes. In DMSO-d6 solution, water favors the decarboxylation. Calculations have been performed to elucidate the mechanism of the decarboxylation in the absence and presence of water. (C) 2018 Elsevier Ltd. All rights reserved.
Subject: Mesoionic compound
N-heterocyclic carbene
Sydnone
Decarboxylation
IR spectroscopy
CONJUGATED MESOMERIC BETAINES
SIGMA-SYDNONYL COMPLEXES
HYDROGEN-BOND
CYCLOADDITION REACTIONS
NUCLEOPHILIC CARBENES
BORANE ADDUCTS
LEWIS PAIR
YLIDES
RING
CHEMISTRY
116 Chemical sciences
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