Asymmetric Cyclopropanation Reactions Research Articles

Chiral Boron‐Bridged Bisoxazolines: Readily Available Anionic Ligands for Asymmetric Catalysis

Asymmetric cyclopropanation and monobenzoylation reactions of meso diols employing borabox catalysts 1 (M=Cu) result in high enantioselectivities. The borabox ligands are anionic analogues of the bisoxazolines 2 and are readily prepared by lithiation of oxazolines and subsequent trapping with boron halides. The considerable potential of borabox ligands in asymmetric catalysis is shown.

Chiral-at-metal ruthenium(II) complexes as catalysts in the asymmetric cyclopropanation reaction

A family of five- and six-coordinate chiral-at-metal ruthenium complexes has been examined as catalysts in the asymmetric cyclopropanation reaction of styrene with ethyl diazoacetate. With complexes 5 and 6, good cis-diastereoselectivity and enantioselectivity up to 74% were observed.

Cover Picture: Asymmetric Cyclopropanation of Optically Active (1‐Diethoxyphosphoryl)vinyl p‐Tolyl Sulfoxide with Sulfur Ylides: A Rationale for Diastereoselectivity (Eur. J. Org. Chem. 4/2005)

AbstractThe cover picture shows the preferred steric course of the reaction of sulfur ylides with enantiopure α‐phosphorylvinyl sulfoxides. The background is crystalline sulfur, rich deposits of which are in south‐eastern Poland. Sulfur and its alchemical emblem symbolize the importance of the stereogenic sulfur atom in this asymmetric cyclopropanation reaction. Details are discussed in the article by M. Miko?ajczyk et al. on p. 653 ff.

The role of binding constants in the efficiency of chiral catalysts immobilized by electrostatic interactions: the case of azabis(oxazoline)-copper complexes.

As shown by theoretical calculations, azabis(oxazoline)-copper complexes are considerably more stable than the analogous bis(oxazoline)-copper complexes. This enhanced stability allows them to be efficiently immobilized by means of electrostatic interactions to different anionic supports, such as clays and nafion-silica nanocomposites, without the loss of a ligand, as is observed for bis(oxazolines). As a result, enantioselectivities of around 90 % ee are obtained in the cyclopropanation reaction between styrene and ethyl diazoacetate. Moreover, the solid catalyst is easily recoverable.

Dirhodium Tetraprolinate Catalyzed Asymmetric Cyclopropanations with High Turnover Numbers.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Asymmetric Cyclopropanation and Aziridination Reactions of Olefins Catalyzed by Cu(I)‐Binaphthyldiimine Complexes.

The chiral Cu(I)-N,N′-bis(2,6-dichlorobenzylidene)-1,1′-binaphthyl-2,2′-diamine complex was found to be an efficient catalyst for asymmetric cyclopropanation and aziridination reactions of olefins with l-menthyl diazoacetate and [N-(p-tolylsulfonyl)imino]phenyliodinane, respectively. Among mono- and disubstituted olefins, 1,1-diarylethylenes showed extremely high enantioselectivities (up to 98% ee) in the cyclopropanation reactions in the presence of a chiral Cu(I)-catalyst (2 mol%). In the case of aziridination reactions catalyzed by the same Cu(I)-catalyst (10 mol%), the reaction of trans-substituted 3-aryl-2-propenoates and 1-substituted trans-3-aryl-2-propen-1-ones showed satisfactory results in term of the enantioselectivities (up to 98% ee).

Dirhodium tetraprolinate-catalyzed asymmetric cyclopropanations with high turnover numbers.

The bridged dirhodium tetraprolinate Rh(2)(S-biTISP)(2) (2) catalyzes the asymmetric cyclopropanation reaction between methyl phenyldiazoacetate and styrene at room temperature with high turnover number (92 000) and turnover frequency (4000 per h). [reaction: see text]

Asymmetric Cyclopropanation and Aziridination Reactions of Olefins Catalyzed by Cu(I)-Binaphthyldiimine Complexes

Abstract The chiral Cu(I)-N,N′-bis(2,6-dichlorobenzylidene)-1,1′-binaphthyl-2,2′-diamine complex was found to be an efficient catalyst for asymmetric cyclopropanation and aziridination reactions of olefins with l-menthyl diazoacetate and [N-(p-tolylsulfonyl)imino]phenyliodinane, respectively. Among mono- and disubstituted olefins, 1,1-diarylethylenes showed extremely high enantioselectivities (up to 98% ee) in the cyclopropanation reactions in the presence of a chiral Cu(I)-catalyst (2 mol%). In the case of aziridination reactions catalyzed by the same Cu(I)-catalyst (10 mol%), the reaction of trans-substituted 3-aryl-2-propenoates and 1-substituted trans-3-aryl-2-propen-1-ones showed satisfactory results in term of the enantioselectivities (up to 98% ee).

The first asymmetric cyclopropanation reactions involving a stable carbene.

The first asymmetric cyclopropanation reactions involving a stable carbene.

Selectivity in reactions of allyl diazoacetates as a function of catalyst and ring size from gamma-lactones to macrocyclic lactones.

Catalytic reactions of diazoacetates tethered through zero, one, two, and three ethylene glycol units to an allyl group have been investigated for chemoselectivity, diastereoselectivity, and enantioselectivity. Results from cyclopropanation, carbon-hydrogen insertion, and oxonium ylide generation are compared from reactions of achiral and chiral catalysts of copper(I) and dirhodium(II) carboxylates and carboxamidates. Relative to results from intermolecular reactions of ethyl diazoacetate with allyl ethyl ether, intermolecular reactions show a diversity of selectivities including preference for the opposite configurational arrangement from the one preferred in corresponding intermolecular cyclopropanation reactions. Enantioselectivities for cyclopropanation are dependent on the catalyst ligands in a manner that reflects divergent trajectories of the carbon-carbon double bond to the reacting carbene center. Enantioselectivity increases as a function of ring size with chiral copper catalysts, but the reverse occurs with chiral dirhodium(II) carboxamidates. Mechanistic implications, including those related to the conformation of the reacting metal carbene, offer a new dimension to understanding of enantioselectivity in catalytic asymmetric cyclopropanation reactions.

ChemInform Abstract: Aza-bis(oxazolines): New Chiral Ligands for Asymmetric Catalysis.

Aza-bis(oxazolines) are introduced as chiral ligands for asymmetric catalysis combining the advantages of easy availability of bis(oxazolines) and backbone variability of aza-semicorrins. Especially, the title ligands could be attached to a polymeric support, which allowed the development of easily recoverable copper(I)-catalysts for asymmetric cyclopropanation reactions.

Total Synthesis and Biological Evaluation of Glycolipids Plakosides A, B and Their Analogs

The total synthesis of plakosides A (1) and B (2), and their designed analogs 3 – 10 was accomplished. The convergent strategy employed involved construction of the individual building blocks employing the Sharpless asymmetric dihydroxylation and the Charette asymmetric cyclopropanation reactions to introduce the desired configuration, followed by their couplings and final elaboration. Thus, key intermediates 12 – 14 were prepared in their optically active forms and joined through a glycosidation reaction and amide-bond formation to yield the target molecules after appropriate elaboration and final deprotection. The synthesized compounds 1 – 10 were evaluated for their immunosuppressive properties in vitro and found to be only modestly active.

Aza-bis(oxazolines): new chiral ligands for asymmetric catalysis

Aza-bis(oxazolines) are introduced as chiral ligands for asymmetric catalysis combining the advantages of easy availability of bis(oxazolines) and backbone variability of aza-semicorrins. Especially, the title ligands could be attached to a polymeric support, which allowed the development of easily recoverable copper(I)-catalysts for asymmetric cyclopropanation reactions.

ChemInform Abstract: Asymmetric Cyclopropanation Reaction under Phase‐Transfer Catalyzed Conditions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Asymmetric cyclopropanation reaction Under phase-transfer catalyzed conditions

An asymmetric cyclopropanation reaction was developed using chiral quaternary ammonium salts as the phase-transfer catalyst (PTC). The reaction smoothly proceeded to give the desired bicyclic compounds with complete stereocontrol in the presence of a catalytic amount of chiral quaternary salts as the PTC, which are derived from readily available chiral amines, with up to 83% ee under mild reaction conditions.

Ru(II)-catalyzed asymmetric cyclopropanation using chiral diphenylphosphino(oxazolinyl)quinoline ligands

Several chiral 8-diphenylphosphino-2-oxazolinylquinolines were synthesized starting from 2-cyano-8-hydroxyquinoline. These N, N, P-chelates were successfully employed in the Ru(II)-catalyzed asymmetric cyclopropanation reactions of diazo-alkenes. The catalytic system exhibited good reactivity and high thermal stability and provided high yields in the intramolecular cyclopropanation, albeit somewhat decreased enantioselectivities compared to known catalytic systems. A dramatic dependency of the enantioselectivity on the substituents of the oxazoline ring was observed.

The synthesis of S-(+)-2,2-dimethylcyclopropane carboxylic acid: a precursor for cilastatin

S-(+)-2,2-Dimethylcyclopropane carboxylic acid, a precursor for cilastatin, was prepared from 2-methylpropene and chiral iron carbene in three steps. Asymmetric cyclopropanation reaction of 2-methylpropene with iron carbene complex having chirality at the carbene ligand, followed by exhaustive ozonolysis, produced S-(+)-2,2-dimethylcyclopropanecarboxylic acid of up to 92% ee. The absolute configuration of complexed chiral cyclopropane (−)- 8 was determined by X-ray crystallographic analysis.

Synthesis and Biological Evaluation of Constrained Phosphonoglutamic Acids as Metabotropic Agents

The synthesis of 3,4-phenylmethano C-2 epimeric phosphonoglutamic acid derivatives is described based on an asymmetric cyclopropanation reaction. The S-isomer exhibited weak binding to human cell lines expressing mGluR4.

ChemInform Abstract: Synthesis of Optically Active 2‐Siloxycyclopropanecarboxylates by Asymmetric Catalysis. Part 4. Influence of Nucleophilicity of Silyl Enol Ethers on Stereoselectivities in Asymmetric Cyclopropanation Reactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis of Optically Active 2‐Siloxycyclopropanecarboxylates by Asymmetric Catalysis, IV. – Influence of Nucleophilicity of Silyl Enol Ethers on Stereoselectivities in Asymmetric Cyclopropanation Reactions

AbstractBy variation of the aryl substituents of silyl enol ethers 1a–e and 1f–k, the influence of their nucleophilicity on the stereochemical outcome of cyclopropanation reactions was studied. Using the neutral Schiff‐base catalyst 2 · Cu(OAc)2, there was only a weak effect. On the other hand, with the cationic bisoxazoline complex 3· CuOTf a remarkable increase in the enantioselectivity was observed with more strongly electron‐attracting substituents such as a trifluoromethyl or nitro group.