Enantioselective Synthesis of Fused Cycloheptadienes by a Tandem Intramolecular Cyclopropanation/Cope Rearrangement Sequence
摘要:
The asymmetric induction in the intramolecular cyclopropanations of allyl vinyldiazoacetates catalyzed by tetrakis[N-[4-dodecylphenyl)sulfonyl]-(S)-prolinato] dirhodium [Rh-2(S-DOSP)(4)] is very dependent on the allyl substitution pattern. The reactions of cis-alkenes result in much higher asymmetric induction than trans-alkenes while the highest enantioselectivity was obtained with a disubstituted terminal alkene. The intramolecular cyclopropanation of dienylmethyl vinyldiazoacetates results in the synthesis of fused cycloheptadiene ring systems with full control of relative stereochemistry and variable enantioselectivity. The synthetic utility of this process was demonstrated by a short synthesis of 5-epi-tremulenolide in 93% ee.
Asymmetric Reactions Catalyzed by Chiral Metal Complexes. LXX. Steric and Electronic Effects of Substrates and Rhodium Chiral Catalysts in Asymmetric Cyclopropanation.
作者:Kiyoshi YOSHIKAWA、Kazuo ACHIWA
DOI:10.1248/cpb.43.2048
日期:——
We have prepared several new, efficient, chiral N-acyl pyrrolidine carboxylic acid ligands for dirhodium-catalyzed asymmetric cyclopropanation and found that the steric and electronic effects of the rhodium(II) complexes and substrates influenced the enantioselectivity and catalytic activity. These electron-rich catalysts were shown to be efficient for asymmetric cyclopropanation using 1-chloro-1-fluoroethylene as a substrate.
Enhancement of Cyclopropanation Chemistry in the Silver-Catalyzed Reactions of Aryldiazoacetates
作者:Janelle L. Thompson、Huw M. L. Davies
DOI:10.1021/ja069314y
日期:2007.5.1
AgSbF6 is an effective catalyst for the reactions of donor/acceptor substituted carbenoids and shows a very different reactivity profile from the traditional rhodium-catalyzed reactions. Most notably, cyclopropanation of sterically hindered alkenes is favorable, and products due to a Wolff rearrangement are not observed. Yields of products obtained are often high (54−96%) with excellent diastereoselectivity
A rigid dirhodium(II) carboxylate as an efficient catalyst for the asymmetric cyclopropanation of olefins
作者:Sophie K Bertilsson、Pher G Andersson
DOI:10.1016/s0022-328x(00)00025-5
日期:2000.5
The dirhodium(II) complex 7 of (1S,3R,4R)-2-(p-tert-butylphenylsulphonyl)-2-aza-bicyclo[2.2.1]heptane-3-carboxylic acid (3) (or its enantiomer) was synthesised in four steps from cyclopentadiene, (R)- or (S)-phenylethylamine and methyl glyoxylate. Complex 7 was evaluated as a catalyst in the asymmetriccyclopropanation of alkenes with vinyl- and phenyl-diazoesters, resulting in enantioselectivity of
of vinylcyclopropanes as masked donor–acceptor system toward the stereoselective synthesis of Z-alkylidenetetrahydrofurans. Results of bromenium catalyzed indirect activation of C–C bond of vinylcyclopropanes and concomitant cyclization to alkylidenetetrahydrofuran and other heterocycles have been discussed. The stereoselectiveformation of the Z-isomer is strongly controlled by the extent of destabilization
我们对乙烯基环丙烷作为掩蔽的供体-受体体系对Z-亚烷基四氢呋喃的立体选择性合成的行为进行了详细研究。讨论了溴催化乙烯基环丙烷的C–C键的间接活化以及伴随环化成亚烷基四氢呋喃和其他杂环的结果。Z的立体选择性形成α-异构体受乙烯基环丙烷的一种薄纱构象异构体的去稳定程度的强烈控制。如在DA环丙烷的情况下,发现开环/环化步骤是立体特异性的。C–C键的活化导致紧密的碳共碳中间体,这从立体化学的完全保留中可以明显看出。构型的保留已通过必要的控制实验确定,该实验排除了双重倒置途径的可能性。目前的结果可作为直接的立体化学证据,以支持紧密的离子对中间体与有争议的S N 2途径。已在B3LYP / 6-31G(d)能级理论上进行了2D势能扫描,以获得构象异构体的相对能量。该ž在构象体的相对种群的基础上,对所观察到的选择性进行了解释,并对在M06–2x / 6-31 + G(d)水平上参与反应的中间和过渡态进行
Stereoselective cyclopropanations with vinylcarbenoids
作者:Huw M.L Davies、T.Jeffrey Clark、Linda A Church
DOI:10.1016/s0040-4039(01)93446-x
日期:——
Rhodium(II) acetate catalyzed decomposition of vinyldiazomethanes in the presence of alkenes results in cyclopropanation with a high degree of stereoselectivity.