562870-89-7Relevant academic research and scientific papers
Asymmetric synthesis of heterobimetallic planar chiral ferrocene pallada-/platinacycles and their application to enantioselective aza-claisen rearrangements
Weiss, Marcel,Frey, Wolfgang,Peters, Rene
, p. 6365 - 6372 (2012)
Ligand exchange reactions are usually slower for Pt(II) in comparison to Pd(II) centers. Mainly for that reason Pt(II) catalysts have often shown a reduced catalytic activity as compared to their Pd(II) counterparts. We are interested in the question if t
Cooperative bimetallic asymmetric catalysis: Comparison of a planar chiral ruthenocene bis-palladacycle to the corresponding ferrocene
Hellmuth, Tina,Rieckhoff, Stefan,Weiss, Marcel,Dorst, Konstantin,Frey, Wolfgang,Peters, Rene
, p. 1850 - 1858 (2014/06/24)
Cooperative asymmetric catalysts often offer advantages in terms of activity, stereoselectivity, and generality as compared to more traditional single point activation catalysts. In cooperative bimetallic catalysis, the intermetallic distance is a crucial parameter for the outcome of a reaction and an optimal synergy of both metal centers. We have recently developed a number of catalytic asymmetric reactions, which are efficiently catalyzed by a planar chiral ferrocene based bispalladacycle and for which the cooperativity of two Pd centers has already been demonstrated. To get more insight into the role of the Pd/Pd distance in such metallocene bismetallacycles, in the present study a corresponding ruthenocene based Pd2-complex has been prepared by the first direct diastereoselective biscyclopalladation of a chiral ruthenocene ligand. In addition, the first highly diastereoselective direct monocyclopalladation of a homochiral ruthenocene is reported. The effect of the increased Cp/Cp distance within the ruthenocene bispalladacycle has been examined in four catalytic asymmetric applications: the aza-Claisen rearrangement of Z-configured allylic N-aryltrifluoroacetimidates, the direct 1,4-addition of α-cyanoacetates to enones, a tandem azlactone formation/1,4-addition to enones and a tandem reaction to form quaternary α-aminosuccinimides by in situ azlactone formation, 1,4-addition to a nitroolefin, and a Nef-type nitro-to-carbonyl transformation as key steps. For each reaction studied, it was found that with some substrates the ferrocene based catalyst is superior, whereas for other substrates the ruthenocene backbone is more favorable. The ruthenocene based bispalladacycle can thus be considered to be a useful and complementary alternative for cooperative bimetallic catalysis.
The asymmetric aza-claisen rearrangement: development of widely applicable pentaphenylferrocenyl palladacycle catalysts
Fischer, Daniel F.,Barakat, Assem,Xin, Zhuo-Qun,Weiss, Matthias E.,Peters, Rene
supporting information; scheme or table, p. 8722 - 8741 (2010/03/31)
Systematic studies have been performed to develop highly efficient catalysts for the asymmetric aza-Claisen rearrangement of trihaloacetimidates. Herein, we describe the stepwise development of these catalyst systems involving four different catalyst generations finally resulting in the development of a planar chiral pentaphenylferrocenyl oxazoline palladacycle. This complex is more reactive and has a broader substrate tolerance than all previously known catalyst systems for asymmetric aza-Claisen rearrange-ments. Our investigations also reveal that subtle changes can have a big impact on the activity. With the enhanced catalyst activity, the asymmetric aza-Claisen rearrangement has a very broad scope: the methodology not only allows the formation of highly enantioenriched primary allylic amines, but also secondary and tertiary amines; al-lylic amines with N-substituted quaternary stereocenters are conveniently accessible as well. The reaction conditions tolerate many important functional groups, thus providing stereoselective access to valuable functionalized building blocks, for example, for the synthesis of unnatural amino acids. Our results suggest that face-selective olefin coordination is the enantioselectivitydetermining step, which is almost exclusively controlled by the element of planar chirality.
Synthesis of nearly enantiopure allylic amines by aza-Claisen rearrangement of Z-configured allylic trifluoroacetimidates catalyzed by highly active ferrocenylbispalladacycles
Jautze, Sascha,Seiler, Paul,Peters, Rene
experimental part, p. 1430 - 1444 (2009/04/06)
The development of the first highly active enantioselective catalyst for the aza-Claisen rearrangement of Z-configured allylic trifluoroacetimidates generating valuable almost enantiopure protected allylic amines is described. Usually Z-configured allylic
Macrocyclic ferrocenyl-bisimidazoline palladacycle dimers as highly active and enantioselective catalysts for the Aza-Claisen rearrangement of Z-configured N-para-methoxyphenyl trifluoroacetimidates
Jautze, Sascha,Seiler, Paul,Peters, Rene
, p. 1260 - 1264 (2008/03/27)
(Chemical Equation Presented) In just four steps from ferrocene, macrocyclic ferrocenyl bispalladacyles have been synthesized by using a diastereoselective biscyclopalladation reaction as the key step. The complexes not only possess a fascinating structur
Practical, highly active, and enantioselective ferrocenyl-imidazoline palladacycle catalysts (FIPs) for the aza-claisen rearrangement of N-para-methoxyphenyl trifluoroacetimidates
Weiss, Matthias E.,Fischer, Daniel F.,Xin, Zhuo-Qun,Jautze, Sascha,Schweizer, W. Bernd,Peters, Rene
, p. 5694 - 5698 (2008/02/04)
Just a pinch of catalyst: Just 0.05 mol % of a novel planar chiral ferrocenyl-imidazoline palladacycle catalyst (FIP) is sufficient to catalyze a highly efficient aza-Claisen rearrangement of N-para-methoxyphenyl trifluoroacetimidates and thereby provide access to chiral protected primary allylic amines with unprecedentedly high enantioselectivities (see scheme). (Chemical Equation Presented).
Catalytic asymmetric synthesis of chiral allylic amines. Evaluation of ferrocenyloxazoline palladacycle catalysts and imidate motifs
Anderson, Carolyn E.,Donde, Yariv,Douglas, Christopher J.,Overman, Larry E.
, p. 648 - 657 (2007/10/03)
(Chemical Equation Presented) Palladium(II) catalysts based on a ferrocenyloxazoline palladacyclic (FOP) scaffold were synthesized and evaluated for the rearrangement of prochiral allylic N-(4-methoxyphenyl)benzimidates. When iodide-bridged dimer FOP precatalysts are activated by reaction with excess silver trifluoroacetate, the allylic rearrangement of both E and Z prochiral primary allylic N-(4-methoxyphenyl)-benzimidates takes place at room temperature to give the corresponding chiral allylic N-(4-methoxyphenyl)benzamides in high yield and good ee (typically 81-95%). Several allylic imidate motifs were evaluated also. Because the corresponding enantioenriched allylic amide products can be deprotected in good yield to give enantioenriched allylic amines, allylic N-aryltrifiuoroacetimidates were identified as promising substrates.
Catalytic asymmetric rearrangement of allylic N-aryl trifluoroacetimidates. A useful method for transforming prochiral allylic alcohols to chiral allylic amines.
Overman, Larry E,Owen, Carolyn E,Pavan, Mary M,Richards, Christopher J
, p. 1809 - 1812 (2007/10/03)
[reaction: see text] A useful method for the conversion of prochiral allylic alcohols to chiral allylic amines of high enantiopurity is reported. N-(4-Methoxyphenyl)trifluoroacetimidates are excellent substrates for the palladium(II)-catalyzed allylic imi
