In this work, we provide a brief overview of the role of N-aryl substituents on triazolium N-heterocyclic carbene (NHC) catalysis. This synopsis provides context for the disclosed synthetic protocol for new chiral N-heterocyclic carbene (NHC) triazoliumsalts with brominated aromatic motifs. Incorporating brominated aryl rings into NHC structures is challenging, probably due to the substantial steric
Chiral Bifunctional N-Heterocyclic Carbenes: Synthesis and Application in the Aza-Morita-Baylis-Hillman Reaction
作者:Song Ye、Lin He、Yan-Rong Zhang、Xue-Liang Huang
DOI:10.1055/s-2008-1067216
日期:2008.9
A series of chiral bifunctional N-heterocyclic carbene (NHC) precursors with a proximal hydroxy group were smoothly prepared from l-pyroglutamic acid. Promising enantiomeric excesses (up to 44% ee) were achieved for the bifunctional NHC-catalyzed enantioselective aza-Morita-Baylis-Hillman reaction of cyclopent-2-enone with N-tosylphenylmethanimine.
Chiraltriazolium salts bearing a pyridine ring were developed as N-heterocyclic carbene precursors. In the presence of the chiraltriazoliumsalt and a base, the catalytic asymmetricbenzoin condensation proceeded to afford the product in high level of chemical yield and enantioselectivity. A wide range of aromatic aldehydes were applicable to this reaction.
Asymmetric Dimerization of Disubstituted Ketenes Catalyzed by N-Heterocyclic Carbenes
作者:Hui Lv、Yan-Rong Zhang、Xue-Liang Huang、Song Ye
DOI:10.1002/adsc.200800532
日期:——
A series of chiral N-heterocycliccarbenes (NHCs), derived from L-pyrogutamic acid, were found to be efficient catalysts for the asymmetricdimerization of alkylarylketenes to give the corresponding α-quaternary β-alkylidenyl-β-lactones in good yields with up to 97% ee. A chiral NHC with a proximal hydroxy group is superior in comparison with the corresponding NHC with its hydroxy group protected.
[4+2] Cycloaddition of Ketenes with<i>N</i>-Benzoyldiazenes Catalyzed by N-Heterocyclic Carbenes
作者:Xue-Liang Huang、Lin He、Pan-Lin Shao、Song Ye
DOI:10.1002/anie.200804487
日期:2009.1
Enantioselectivity switch: A catalytic enantioselective [4+2] cycloaddition reaction of alkylarylketenes with N‐aryl‐N′‐benzoyldiazenes or N,N′‐dibenzoyldiazenes to give 1,3,4‐oxadiazin‐6‐ones 1 was developed by employing N‐heterocyclic carbene (NHC) catalysts. The enantioselectivities could be switched for most reactions by changing the substituents on the NHC catalyst. TBS=tert‐butyldimethylsilyl