Unexpected Reaction of Dimethyl Acetylenedicarboxylate with in Situ Generated Arylketenes Catalyzed by 1-Methylimidazole

Direct synthesis of 2,4,5-trisubstituted imidazoles from primary alcohols by diruthenium(ii) catalysts under aerobic conditions

A straightforward synthetic approach to 2,4,5-trisubstituted imidazoles from readily available primary alcohols using arene diruthenium(ii) catalysts has been described.

DABCO-mediated isocyanide-based multicomponent reaction: synthesis of highly substituted cyclopentenes

Highly substituted cyclopentenes can be accessed rapidly from isocyanides, aldehydes and malononitrile or ethyl cyanoacetate (AB₂C₂) using DABCO as a catalyst under solvent-free conditions at 40 °C within 30 min.

N-heterocyclic carbene catalyzed transformations of 3-halopropenals to the equivalents of beta-acylvinyl anions

3-Halopropenals 1 can behave as an alternative equivalent of beta-acylvinyl anions (I) in the presence of N-heterocyclic carbene precursor (IPr.HCl) and DBU to afford cyclic alpha,beta-unsaturated carbonyl derivatives, butenolides 4 and pyrazolone 6, after cyclization with 2 and 5, respectively.

DFT study on the mechanisms of stereoselective C2-vinylation of 1-substituted imidazoles with 3-phenyl-2-propynenitrile

Recently, the first examples of direct vinylation of 1-substituted imidazoles at the 2-position of the imidazole nucleus have been described (J. Org. Chem. 2008, 73, 9155-9157). 1-Substituted imidazoles are C(2)-vinylated with 3-phenyl-2-propynenitrile at room temperature without catalyst and solvent to afford 3-(1-organyl-1H-imidazol-2-yl)-3-phenyl-2-propenenitriles, mainly (ca. 95%) as (Z)-isomers, in 56-88% yield. Nevertheless, the stereoselectivity of vinylation, which has been elusive over the past decades, is still a big problem to explain. In this paper, the reaction mechanisms of stereoselective C(2)-vinylation of 1-methylimidazole with 3-phenyl-2-propynenitrile have been investigated using density functional theory (DFT). The geometries of the reactants, transition states, intermediates, and products were optimized at the B3LYP/6-31G(d,p) level. The calculated results reveal that the reaction contains three processes: formation of zwitterion, proton transfer, and ring rearrangement. Four possible reaction channels are shown, including two (E)-isomer channels and two (Z)-isomer channels. One of the (Z)-isomer channels has the lowest energy barrier among all the four channels, with the highest energy barrier for 83.62 kJ/mol, so it occurs more often than the others at room temperature, which is in good agreement with experiment. Further calculations of solvation effects show that the title reaction can be carried out more smoothly in the gas phase.

Novel Annulation Reactions of Aryl Methyl Ketenes with Zwitterions Derived from Dimethyl Acetylenedicarboxylate and N-Alkylimidazoles

[reaction: see text] A novel three-component annulation reaction involving N-alkylimidazoles, dimethyl acetylenedicarboxylate, and in situ generated aryl methyl ketenes leading to the synthesis of 6-vinyl-1,3a-diazapentalene derivatives is reported.