Catalysts For Cyclopropanation Research Articles

Optimization or Breakthrough? The First Highly cis- and Enantioselective Asymmetric Cyclopropanation of 1-Octene by “Electronic and Counterion” Tuning of [RuCl(PNNP)]+ Catalysts

The dichloro complexes [RuCl2(1a)] (2a) and [RuCl2(1b)] (2b) with the chiral tetradentate PNNP ligands (1S,2S)-N,N‘-bis[o-(diphenylphosphino)benzylidene]cyclohexane-1,2-diamine (1a) and (1S,2S)-N,N‘-bis[o-(bis(4-trifluoromethylphenyl)phosphino)benzylidene]cyclohexane-1,2-diamine (1b) react with AgSbF6 (1 equiv) to give the highly reactive five-coordinate complexes [RuCl(PNNP)]SbF6 (3aSbF6 or 3bSbF6), which were characterized in solution. The reaction of 2a or 2b with AgBF4 gives [RuCl(PNNP)]BF4 along with unidentified products. Complex [RuCl(1b)]SbF6 (3bSbF6) cyclopropanates 1-octene to ethyl 2-hexylcyclopropane-1-carboxylate (up to 66% overall isolated yield) in the presence of ethyl diazoacetate with unprecedented cis-diastereoselectivity (85:15 cis:trans ratio) and with excellent enantioselectivity (up to 99 and 98% ee for the cis and trans isomers, respectively). Complex 3bSbF6 is also an excellent cis-selective cyclopropanation catalyst for styrene (96% ee for the cis isomer, 99:1 cis:trans ratio) and α-methylstyrene (96% ee for the cis isomer, 92:8 cis:trans ratio). The catalyst activity depends on the counterion and increases in the order [BF4]- < [SbF6]- < [PF6]-, whereas the best stereoselectivity is observed with [SbF6]-. Molecular modeling calculations are extended to 1-octene and α-methylstyrene and revised to account for the absolute configuration of ethyl cis-2-phenylcyclopropane-1-carboxylate (1S,2R, incorrectly reported as 1R,2S in a former paper).

Dinuclear ruthenium(I) complexes of the type [Ru 2(CO) 4L 2] with carboxylate or 2-pyridonate ligands: Evaluation as catalysts for olefin cyclopropanation with diazoacetates

Dinuclear ruthenium(I,I) carboxylate complexes [Ru 2(CO) 4(μ-OOCR) 2] n (R = CH 3 ( 1a), C 3H 7 ( 1b), H ( 1c), CF 3 ( 1d)) and 2-pyridonate complex [Ru 2(CO) 4(μ-2-pyridonate) 2] n ( 3) catalyze efficiently the cyclopropanation of alkenes with methyl diazoacetate. High yields are obtained with terminal nucleophilic alkenes (styrene, ethyl vinyl ether, α-methylstyrene), medium yields with 1-hexene, cyclohexene, 4,5-dihydrofuran and 2-methyl-2-butene. The E-selectivity of the cyclopropanes obtained from the monosubstituted alkenes and the cycloalkenes decreases in the order 1b > 1a > 1d > 1c. The cyclopropanation of 2-methyl-2-butene is highly syn-selective. Several complexes of the type [Ru 2(CO) 4(μ-L 1) 2] 2 ( 4) and ( 5), [Ru 2(CO) 4(μ-L 1) 2L 2] (L 2 = CH 3OH, PPh 3) ( 6)–( 9) and [Ru 2(CO) 4(CH 3CN) 2(μ-L 1) 2] ( 10) and ( 11), where L 1 is a 6-chloro- or 6-bromo-2-pyridonate ligand, are also efficient catalysts. Compared with catalyst 3, a halogen substituent at the pyridonate ligand affects the diastereoselectivity of cyclopropanation only slightly.

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

AbstractFor Abstract see ChemInform Abstract in Full Text.

Palladium-mediated synthesis of novel meso-chiral porphyrins: cobalt-catalyzed cyclopropanation

A series of novel meso-chiral porphyrins were effectively synthesized from reactions of 5,15-dibromo-10,20-diarylporphyrins with readily available chiral alcohols and amides via palladium-mediated C–N and C–O bond formations. Cobalt complexes of these chiral porphyrins were prepared and shown to be effective catalysts for cyclopropanation of styrene with ethyl diazoacetate under mild and practical conditions, affording the desired cyclopropane ester as a trans-dominant form in excellent yields. Due to orientation and flexibility of the chiral appendages, only low enantioselectivity was observed.

Axial Ligand Effects: Utilization of Chiral Sulfoxide Additives for the Induction of Asymmetry in (Salen)ruthenium(ii) Olefin Cyclopropanation Catalysts

An efficient and facile method is used to develop new (salen)ruthenium(II) catalysts for the asymmetric cyclopropanation of olefins, in which a chiral additive induces asymmetry in inexpensive and readily synthesized achiral (salen)ruthenium(II) catalysts (see scheme; EDA=ethyl diazoacetate). This approach is amenable to parallel-screening optimization and has great potential advantages over traditional catalyst development and synthetic methods. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2005/z460887_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Axial Ligand Effects: Utilization of Chiral Sulfoxide Additives for the Induction of Asymmetry in (Salen)ruthenium(ii) Olefin Cyclopropanation Catalysts

„Chirale“ Veredelung: Ein effizientes Verfahren wird zur Entwicklung neuer (Salen)ruthenium(II)-Katalysatoren für die asymmetrische Cyclopropanierung von Olefinen genutzt. Grundlage ist die Verwendung von chiralen Liganden, die billige und einfach zugängliche achirale (Salen)ruthenium(II)-Katalysatoren in chirale Komplexe überführen (siehe Schema; EDA=Ethyldiazoacetat). Die Methode ist zum Parallelscreening geeignet und weist große Vorteile gegenüber herkömmlichen Verfahren der Katalysatorentwicklung auf.

Synthesis, characterization, and catalytic application of copper(I) nitrile cations with perfluorinated weakly coordinating anions

Complexes of the type [Cu(CH 3 CN) 4 ] + [A] - ([A] - = [B(C 6 F 5 ) 4 ] - (1), [B{C 6 H 3 (CF 3 ) 2 }] - (2), [(C 6 F 5 ) 3 B-C 3 H 4 N 2 -B(C 6 F 5 ) 3 ] - (3)) are synthesized and characterized. Their utilization as catalysts in cyclopropanation and aziridination reactions of olefins, forming three membered rings is explored. The compounds are found to catalyze both reactions in moderate to good yields being the best results obtained with compound 1. The more weakly the nitrile ligands are coordinated to the metal center, the better is the catalytic performance of the catalyst.

Olefin cyclopropanation and insertion into O [sbnd]H bonds mediated by copper(I) and palladium(II) covalently anchored to silica xerogels

Copper(I) and palladium(II) ligated to pyrazolylpyridine bearing a tethered (trimethoxysilyl)propyl group in position 4 of the pyrazole ring were chemically bonded to silica via a sol–gel process. The textural properties of the materials (specific surface area, porous volume, and pore size distribution) were characterized by nitrogen adsorption–desorption isotherms, mercury porosimetry, and TEM analysis. The hybrid materials were tested as catalysts in olefin cyclopropanation and as potential chemoselective catalysts in the reaction with unsaturated alcohols (double bond versus OH group), with ethyl diazoacetate as a carbene precursor, and compared with the corresponding homogeneous complexes.

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.

New chiral Schiff base–Cu(II) complexes as cyclopropanation catalysts

A series of chiral Schiff base ligands 1– 4, derived from ( 1R, 2S)-(+)- cis-1-amino-2-indanol and other chiral amines with substituted salycilaldehydes were synthesized and transformed to the corresponding Cu(II) complexes. Molecular structures of six Cu(II) complexes were determined by X-ray crystallographic studies. The structures show the metal ion in a distorted square planar geometry with dimeric or monomeric structures, depending on the ligand denticity. The potential use of these complexes in asymmetric Cyclopropanation was explored.

Dendritic Metalloporphyrins as Catalysts for Organic Transformations

AbstractFor Abstract see ChemInform Abstract in Full Text.

Copper(I) and silver(I) complexes of 1,5-methylene- and diethylmethylene-bridged bis(oxazoline) ligands. In situ Cu(II)-catalyzed oxidation of methylene bridge

Silver(I) and copper(I) complexes of C 2-symmetric bis(oxazoline) ligands were studied by UV, NMR, IR, EPR and ES-MS spectroscopies. The stability constants of the Ag– 1a and Ag– 1b complexes with 1:1 and 1:2 stoichiometries in acetonitrile were determined by NMR spectrometric titrations. The evidence of tetrahedral coordination for complex (Ag( 1a ) 2( + was obtained from the complexation induced shifts (CIS) and NOEs. Mass spectra revealed the Cu(II) mediated oxidation of methylene bridge in copper complexes of 1a and 1b , which was in accordance with the UV, NMR, IR and EPR findings. The efficiency of Cu(I) complexes of methylene-bridged 1,5-bis(oxazoline)s 1 as chiral catalysts in stereoselective cyclopropanation of styrene with ethyl diazoacetate, was compared to that of the dialkylmethylene-bridged 1,5-bis(oxazoline)s 2 .

Chiral 2-pyridyl alcoholate copper complexes: crystal structures of [bis(2-pyridyl alcoholate)copper(II)] and the use of [(2-pyridyl alcoholate)copper(II)] +and [(2-pyridyl alcoholate)copper(I)] in asymmetric cyclopropanation of styene and allylic oxidation of cyclohexene

Chiral N,O pyridine alcohols HL 1– HL 6 were used to form complexes with copper(II) ions. Ligands HL 1 and HL 2 formed complexes with copper(II) ions when Cu(OAc) 2 and HL were refluxed in methanol/ethanol mixture. Ligand HL 3 formed a complex with copper(II) when deprotonated with NaH and stirred in a Cu(II) acetate THF solution. Ligands HL 4– HL 6 did not form complexes with copper(II) under similar conditions. Two complexes, [Cu( L 1) 2] and [Cu( L 2) 2], were isolated as single crystals and characterized by X-ray crystallography. These complexes showed low catalytic activities in asymmetric reactions. However, they became active when reacted with triflic acid. Copper complexes, [Cu( L)] or [Cu( L)] +, formed in situ by reacting ligands HL with copper(I) or (II) ions, respectively, were also found to be active copper catalysts for asymmetric cyclopropanation of styrene with ethyl diazoacetate and allylic oxidation of cyclohexene with t-butylperoxybenzoate. Enantioselectivities up to 56% and 38% were obtained in asymmetric cyclopropanation of styrene and asymmetric allylic oxidation of cyclohexene, respectively.

Vitamin B12 Derivatives as Natural Asymmetric Catalysts: Enantioselective Cyclopropanation of Alkenes.

Vitamin B(12) derivatives were found for the first time to be general and efficient catalysts for asymmetric cyclopropanation of alkenes with ethyl diazoacetate (EDA). Among several common derivatives, aquocobalamin (B(12a)) was shown to be the most effective catalyst for a variety of alkenes, providing cis-dominant cyclopropanes in excellent yields and moderate enantioselectivity. Reactivity studies under different conditions suggest that the active species in the proposed catalytic cycle is the base-on cob(II)alamin (B(12r)) that is generated possibly via in situ reduction of B(12a) by EDA.

Simple Strategy for the Immobilization of Dirhodium Tetraprolinate Catalysts Using a Pyridine‐Linked Solid Support.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Monomeric Rhodium(II) Catalysts for the Preparation of Aziridines and Enantioselective Formation of Cyclopropanes from Ethyl Diazoacetate at Room Temperature.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Metallophthalocyanines as Potent Catalysts for Cyclopropanation of Olefins with Ethyldiazoacetate

Copper, manganese and iron phthalocyanines were found to be highly efficient catalysts for cyclopropanation of olefins using ethyldiazoacetate as carbene precursor. In general copper(II)-phthalocyanine was found to be the most active catalyst followed by the Mn(II)Pc and Fe(II)Pc. Ni(II)Pc and Co(II)Pc were found to be the less active catalysts for this reactions.

Simple strategy for the immobilization of dirhodium tetraprolinate catalysts using a pyridine-linked solid support.

Dirhodium tetracarboxylates are readily immobilized on agitation in the presence of highly cross-linked polystyrene resins with a pyridine attachment. A systematic study demonstrates that the polymer backbone, the linker, the terminal pyridine group, and the catalyst structure all contribute to the efficiency of dirhodium catalyst immobilization. The immobilization is considered to be due to the combination of ligand coordination and encapsulation. The dirhodium tetraprolinate catalysts, Rh2(S-DOSP)4 (1a), Rh2(S-TBSP)4 (1b), and Rh2(S-biTISP)2 (2), are all efficiently immobilized. The resulting heterogeneous complexes are very effective catalysts for asymmetric cyclopropanation between methyl phenyldiazoacetate and styrene, and under optimized conditions they can be recycled five times with virtually no loss in enantioselectivity. The three-phase test studies indicated that a very slow reaction occurs when both the catalyst and the diazo compound were immobilized, but the slow rate precluded the likelihood that the cyclopropanation was predominately occurring by a release-and-capture mechanism.

Vitamin B12 derivatives as natural asymmetric catalysts: enantioselective cyclopropanation of alkenes.

Vitamin B(12) derivatives were found for the first time to be general and efficient catalysts for asymmetric cyclopropanation of alkenes with ethyl diazoacetate (EDA). Among several common derivatives, aquocobalamin (B(12a)) was shown to be the most effective catalyst for a variety of alkenes, providing cis-dominant cyclopropanes in excellent yields and moderate enantioselectivity. Reactivity studies under different conditions suggest that the active species in the proposed catalytic cycle is the base-on cob(II)alamin (B(12r)) that is generated possibly via in situ reduction of B(12a) by EDA.

Diastereoselective and Enantioselective Cyclopropanation of Alkenes Catalyzed by Cobalt Porphyrins.

AbstractFor Abstract see ChemInform Abstract in Full Text.