含窒素複素環式カルベン化学の新展開 : 有機触媒としての利用 [in Japanese] New Developments in the N-Heterocyclic Carbene Chemistry : Application as Organocatalysts [in Japanese]
Access this Article
Search this Article
N-heterocyclic carbenes have been studied for their abilities to catalyze C-C bond formation/cleavage and asymmetric reactions. N-heterocyclic carbenes generated from imidazolium, benzimidazolium, triazolium, pyrido[1, 2-c]imidazolium, pyrido[2, 1-c]triazolium, and dipyrido[1, 2-c : 2'1'-e]imidazolium iodide were found to be effective catalysts in benzoin condensation. The acidity of the azolium salts at the C2-hydrogen of the imidazolium or the triazolium moieties relates to the base effect on the reaction. These carbenes can also be employed in retro-benzoin condensation, which is a new method of synthesizing ketones by C-C bond cleavage of α-substituted benzoins. Chloro and fluoro groups of haloarenes are nucleophilically substituted by aroyl groups originated from aromatic aldehydes by catalytic action of imidazolidenyl and triazolidenyl carbenes to afford ketones. N-heterocyclic carbenes mediate the addition of trimethylsilylcyanide to aldehydes to yield cyanohydrin trimethylsilyl ethers. The use of chiral imidazolidenyl carbene derived from (R, R)-1, 3-bis[(1-naphthyl)ethyl] imidazolium chloride led to enantioseletive cyanosilylation. C<SUB>2</SUB>-symmetric imidazolidenyl carbenes catalyze asymmetric acylation of racemic secondary alcohols.
- J. Synth. Org. Chem. Jpn.
J. Synth. Org. Chem. Jpn. 66(4), 377-386, 2008-04-01
The Society of Synthetic Organic Chemistry, Japan