Enantioselective Cyclopropanation Of Styrene Research Articles

Non-covalent immobilization of chiral copper complexes on Al-MCM41: Effect of the nature of the ligand

Cu-Al-MCM41, prepared by deposition of copper(II) triflate with incipient wetness impregnation and thermal treatment under air flow, can be modified with different chiral ligands of the bis(oxazoline) family. The efficiency of the supported chiral catalysts in the enantioselective cyclopropanation of styrenes with ethyl diazoacetate depends on the nature of the ligand. The azabis(oxazolines) perform much better than the bis(oxazolines) and give stable catalysts that can be used for at least five consecutive runs, with productivities that can reach values close to 1000 molecules of cyclopropane per copper site. The best enantioselectivities obtained with these catalysts are in the range of 60–70% ee in the reaction at 90°C.

Catalytic activity of copper-bis(oxazoline) grafted on mesoporous silica in enantioselective cyclopropanation

Chiral phenyl substituted bis(oxazoline) (PhBox) was covalently immobilized through carbamate linkers onto mesoporous silica materials. These supports were previously prepared by the sol–gel method and they exhibit different textural properties. The presence and the integrity of the bis(oxazoline) ligand was checked by 13C-CP-MAS-NMR. These chiral mesoporous materials were complexed with copper(II) triflate. In spite of the different textural properties of these supports, the copper loading, determined by ICP-AES, was nearly the same (0.041–0.044 mmol Cu/g of solid). The supported Cu(II) complexes were tested as catalysts in the enantioselective cyclopropanation of styrene with ethyl diazoacetate. Enantioselectivities are consistently lower than those obtained in homogeneous phase. Different analyses point to a difficulty in the formation of the expected chelate, due to the presence of a coordinating functional group in the linker, as responsible for the loss in enantioselectivity. The textural properties of the materials do significantly affect the behavior upon recovery.

Synthesis of Chiral C2‐Symmetric Methylene‐ and Boron‐Bridged Bis(imidazolines).

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Synthesis of Chiral C2-Symmetric Methylene- and Boron-Bridged Bis(imidazolines)

A series of C 2-symmetric boron-bridged bis(imidazolines) was obtained by lithiation of 2-imidazolines and subsequent reaction with dialkyl- or diarylhaloboranes. The corresponding 2-imidazolines were prepared by an efficient four-step sequence starting from N-tert-butoxycarbonyl-protected α-amino acids. C 2-Symmetric methylenebis(imidazolines) were readily synthesized from chiral diamines by condensation with diethyl malonimidate. The bis(imidazolines) were used as ligands in the enantioselective cyclopropanation of styrene and allylic oxidation of cyclic alkenes.

Synthesis of Novel Chiral Semicrown Ether‐Like Bis(oxazoline) Ligands and Application in Enantioselective Cyclopropanation of Styrene.

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Synthesis of Novel Chiral Semicrown Ether‐Like Bis(oxazoline) Ligands and Application in Enantioselective Cyclopropanation of Styrene

A series of chiral C2‐symmetric bis(oxazoline) ligands containing semicrown ether unit were synthesized. The copper complexes prepared in situ from copper(I)‐triflate, and the new chiral oxazoline ligands were assessed as chiral catalysts in the enantioselective cyclopropanation of styrene with diazoacetates. Enantioselectivities up to 84% and up to 65%, respectively, for trans‐ and cis‐2‐phenylcyclopropanecarboxylate were observed.

Synthesis of Novel Chiral Bisoxazoline Ligands Containing 2,5‐Diaryl‐1,3,4‐oxadiazole and Enantioselective Cyclopropanation of Styrene.

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Novel chiral dibenzo[ a, c]cycloheptadiene bis(oxazoline) and catalytic enantioselective cyclopropanation of styrene

A series of chiral C 2-symmetric bis(oxazoline) ligands containing dibenzo[ a, c]cycloheptadiene units were synthesized. The copper complexes, prepared in situ from copper (I)-triflate and the new enantiopure oxazoline ligands, were assessed as chiral catalysts in the enantioselective cyclopropanation of styrene with diazoacetate. Enantioselectivities up to 82 and 62%, respectively, for trans- and cis-2-phenylcyclopropanecarboxylate were observed.

Synthesis of Novel Chiral Bisoxazoline Ligands Containing 2,5-Diaryl-1,3,4-oxadiazole and Enantioselective Cyclopropanation of Styrene

Practical synthesis of chiral C 2-symmetric substituted bisoxazoline ligands containing 2,5-diaryl-1,3,4-oxadiazole units was investigated. Five chiral bisoxazoline ligands containing 2,5-diphenyl-1,3,4-oxadiazole have been synthesized from 2,5-di-(o-carboxylphenyl)-1,3,4-oxadiazole and amino alcohols by methanesulfonyl chloride or p-toluenesulfonyl chloride assisted cyclization via hydroxy amide intermediate. Preliminary examination of copper complexes of new ligands as chiral catalysts in the enantioselective cyclopropanation of styrene with ethyl diazoacetate was performed. Enantioselectivities up to 35% ee and 87% ee for trans- and cis-2-phenylcyclopropanecarboxylate, respectively were observed.

ChemInform Abstract: Novel Chiral Di‐2‐pyridyl Ketone Ligands: Crystal Structure of a Copper Complex and Its Activity in the Copper‐Catalyzed Enantioselective Cyclopropanation of Styrene.

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Mesopore immobilised copper bis(oxazoline) complexes for enantioselective catalysis.

New supported heterogeneous catalysts have been synthesised through the tethering of copper bis(oxazoline) complexes to the surfaces of MCM-41 and MCM-48 mesoporous materials, and the prepared catalysts shown to be highly active in the enantioselective cyclopropanation of styrene with ethyl diazoacetate.

Highly efficient and enantioselective cyclopropanation of styrene with diazoacetates using a new copper-(Schiff-base) catalyst

A new copper-(Schiff-base) complex, derived from ( S)-2-amino-1,1-di(3,5-di- t-butylphenyl)propanol, 2-hydroxy-5-nitrobenzaldehyde and copper acetate monohydrate, was used as an efficient catalyst for the cyclopropanation of styrene with diazoacetates, affording ees of up to 98%.

Asymmetrische Katalysen, 116. Triaza-und Tetraaza-Makrocyclen mit chiralen "pendant arms" in der enantio- selektiven Cyclopropanierung / Asymmetrie Catalyses, 116. Triaza and Tetraaza Macrocycles with Chiral Pendant Arms in the Enantioselective Cyclopropanation

The chiral ligands 1 - 5 were tested in the Cu1- catalyzed enantioselective cyclopropanation of styrene with ethyl diazoacetate. The new ligand 5 was synthesized by reaction of 1,4,8,11-tetraazacyclotetradecane (cyclam ) with (S)-propylene oxide and characterized by X-ray analysis.

Chiral enamines derived from 2‐(2′‐pyrido)acetophenone and 2‐(2′‐quinolino)acetophenone as ligands in copper(I) catalyzed enantioselective cyclopropanations

AbstractOptically active enamines of 2‐(2′‐pyrido)acetophenone or 2‐(2′‐quinolino)acetophenone with (R)‐1‐phenylethylamine, (R)‐1‐(1‐naphthyl)ethylamine, (R)‐cyclohexylethylamine, and (R)‐phenylglycinol were prepared and their copper(I) complexes used in the enantioselective cyclopropanation of styrene with ethyl‐ and menthyldiazoacetate. Enantioselectivities of up to 42% enantiomeric excess were obtained for cis/trans 2‐phenylcyclopropan‐1‐carboxylic acid ethyl esters, as determined by gas‐liquid chromatography (GLC) on chiral chromatographic columns. © 1995 Wiley‐Liss, Inc.

Asymmetric catalysis: LXXX. An optically-active tetrakispyrazolylborate: Synthesis and use in Cu-catalysed enantioselective cyclopropanation

The synthesis of the optically-active sodium salt of tetrakis(4,5,6,7-tetrahydro-7,8,8-trimethyl-2 H-4,7-methanoindazolyl)borate, [NaB-(camphpz) 4] ( 1) is reported. Cu-based in situ catalysts containing [NaB(camphpz) 4] give an enantiomeric excess of up to 62% in the enantioselective cyclopropanation of styrene with ethyl diazoacetate.