Suzuki–Miyaura Cross-Coupling Reactions in Acetic Acid Employing Sydnone-Derived Catalyst Systems

Abstract

The catalyst system consisting of lithium N-phenylsydnone-4-carboxylate/Pd(PPh3)4 has proven to be an effective catalyst for the Suzuki–Miyaura reaction of 2,4-dinitrochlorobenzene with boronic acids in acetic acid at pH 5.7, whereas the N-phenylsydnone carbene palladium complex [sydPd(PPh3)2Br] required pH 8.0.

A DFT and ab initio study of conjugated and semi-conjugated mesoionic rings and their covalent isomers

“…The subtle difference between semi-conjugated and pseudo semi-conjugated HMBs (and also between cross-conjugated and pseudo cross-conjugated HMBs) has been described previously. 1,5 A comprehensive classification system requires this distinction but in practice the pseudo species appear to have very similar properties to the non-pseudo species and for routine discussion, but not always, 6,7 the distinction is probably not necessary.…”

The relative stability of mesoionic and N-heterocyclic carbene tautomers: a computational study of substituent effects

“…The SESE values of anionic 3-substituents suggest the possibility that for nitron 1 it might be the anionic NHC 22 that is the reactive intermediate leading to carbene-derived products. In addition to nitron, and its close analogues, [25][26][27]30,31 these conclusions may also be relevant to the NHC character of the other mesoionic anions, 32 including the sydnones. 33 …”

Synthesis, characterization and palladium complex formation of pyridinium- and quinolinium-3-acetylides: mesomeric betaines or betaine-stabilized carbenes?

“…First results have been summarized in a review article. 4 As example, nitron 1 (Scheme 1) is a type A mesoionic compound belonging to class 1B of conjugated mesomeric betaines, 3 and a masked N-heterocyclic carbene. 5 Although it was published in 1905 6,7 and has been applied for decades as reagent to detect nitrates (Busch's reagent), 8,9 it was not shown before 2012 that nitron 1 is in tautomeric equilibrium with its N-heterocyclic carbene 2.…”

“…28e31 By contrast, the use of cross-conjugated heterocyclic mesomeric betaines as masked N-heterocyclic carbenes is rather limited due to the vigorous conditions which are necessary to induce decarboxylations. 4,22 In continuation of our interest in the area of overlap between the classes of heterocyclic mesomeric betaines and N-heterocyclic carbenes we report on structures here in which the carboxylate moiety of trigonelline as well as of its quinoline derivative is formally replaced to acetylide groups. Thus, the pyridinium-or quinolinium-acetylides VII and VIII can be formulated as allenylidenes, respectively, which are stabilized by a conjugated heterocyclic mesomeric betaine (VII) or a non-betainic heterocycle (VIII).…”