[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
Enantioselective Synthesis of Aza-β-lactams via NHC-Catalyzed [2 + 2] Cycloaddition of Ketenes with Diazenedicarboxylates
作者:Xue-Liang Huang、Xiang-Yu Chen、Song Ye
DOI:10.1021/jo901656q
日期:2009.10.2
N-Heterocyclic carbenes were found to be efficient catalysts for the formal [2 + 2] cycloaddition of aryl(alkyl)ketenes and diazenedicarboxylates to give the corresponding aza-β-lactams in good yields with up to 91% ee. The N-substituent (carboxylate vs benzoyl) of diazenes played an important role to control the reaction modes (formal [2 + 2] vs [4 + 2] cycloaddtions).
Asymmetric esterification of ketenes catalyzed by an N-heterocyclic carbene
作者:Xiao-Na Wang、Hui Lv、Xue-Liang Huang、Song Ye
DOI:10.1039/b815139c
日期:——
The chiral N-heterocycliccarbene precursor 2, derived from L-pyroglutamic acid, was found to be an efficient precatalyst for the enantioselective esterification of alkylarylketenes with benzhydrol to give the corresponding esters in good yields with good to high enantioselectivities (up to 95% ee).
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.