Using Soluble Polymers to Enforce Catalyst‐Phase‐Selective Solubility and as Antileaching Agents to Facilitate Homogeneous Catalysis

The enforced phase‐selective solubility of polyisobutylene (PIB)‐bound Rh^II catalysts in biphasic heptane/acetonitrile mixtures can be used not only to recycle these catalysts but also to minimize bimolecular reactions with ethyl diazoacetate. When cyclopropanation and O? H insertion reactions are carried out with PIB‐bound Rh^II catalysts either with or without addition of an unfunctionalized hydrocarbon polymer cosolvent, dimer by‐product formation is suppressed even without slow syringe pump addition of the ethyl diazoacetate. This suppression of by‐product formation is shown to be due to increased phase segregation of the soluble polymer‐bound catalyst and the ethyl diazoacetate reactant. These studies also reveal that added hydrocarbon polymer cosolvents can function as antileaching agents, decreasing the already small amount of a soluble polymer‐bound species that leaches into a polar phase in a biphasic mixture during a liquid/liquid separation step.     

壳聚糖希夫碱铜多相催化剂催化苯乙烯环丙烷化反应研究

壳聚糖希夫碱铜催化剂催化苯乙烯环丙烷化反应，得到了非常好的化学收率，同时还得到了17.1%ee和33.3:66.7的顺反比。此外，催化剂重复使用数次仍保持很高的活性。     

Diastereoselective and enantioselective cyclopropanation of alkenes catalyzed by cobalt porphyrins

Cobalt(II) porphyrin complexes were shown to be general and efficient catalysts for selective cyclopropanation of alkenes with ethyl diazoacetate (EDA). The catalytic system can operate with alkenes as limiting reagents, requiring only stoichiometric amounts of EDA. The protocol is performed in one-pot fashion without the need of slow addition of EDA. The diastereoselectivity of the current system can be tuned by using different porphyrin ligands or additives, giving either trans- or cis-dominant cyclopropanes. The asymmetric cyclopropanation was also demonstrated with the use of chiral cobalt porphyrin complexes.     

Asymmetric inter- and intramolecular cyclopropanation of alkenes catalyzed by chiral ruthenium porphyrins. Synthesis and crystal structure of a chiral metalloporphyrin carbene complex.

Extensive investigations of asymmetric intermolecular cyclopropanation of terminal alkenes with diazoacetates catalyzed by ruthenium porphyrin [Ru(P*)(CO)(EtOH)] (1, H2P = 5,10,15,20-tetrakis[(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracene-9-yl]porphyrin) and the application of catalyst 1 to asymmetric intramolecular cyclopropanation of allylic or homoallylic diazoacetates are described. The intermolecular cyclopropanation of styrene and its derivatives with ethyl diazoacetate afforded the corresponding cyclopropyl esters in up to 98% ee with high trans/cis ratios of up to 36 and extremely high catalyst turnovers of up to 1.1 x 10(4). Examination of the effects of temperature, diazoacetate, solvent, and substituent in the intermolecular cyclopropanation reveals that (i) both enantioselectivity and trans selectivity increase with decreasing temperature, (ii) sterically encumbered diazoacetates N2CHCO2R, such as R = Bu(t), and donor solvents, such as diethyl ether and tetrahydrofuran, are beneficial to the trans selectivity, and (iii) electron-donating para substituents on styrene accelerate the cyclopropanations, with the log(k(X)/k(H)) vs sigma(+) plot for para-substituted styrenes p-X-C6H4CH=CH2 (X = MeO, Me, Cl, CF3) exhibiting good linearity with a small negative rho(+) value of -0.44 +/- 0.09. In the case of intramolecular cyclopropanation, complex 1 promoted the decomposition of a series of allylic diazoacetates to form the cyclopropyl lactones in up to 85% ee, contributing the first efficient metalloporphyrin catalyst for an asymmetric intramolecular cyclopropanation. Both the inter- and intramolecular cyclopropanations were proposed to proceed via a reactive chiral ruthenium carbene intermediate. The enantioselectivities in these processes were rationalized on the basis of the X-ray crystal structures of closely related stable chiral carbene complexes [Ru(P*)(CPh2)] (2) and [Ru(P*)(C(Ph)CO2CH2CH=CH2)] (3) obtained from reactions of complex 1 with N2CPh2 and N2C(Ph)CO2CH2CH=CH2, respectively.     

Carbenoid transfer in competing reactions catalyzed by ruthenium complexes

Aiming at improving catalyst activity, ten ruthenium promoters have been investigated in carbenoid transfer from ethyl diazoacetate to styrene as a model substrate. Optimal selectivity in cyclopropanation has been attained with the new NHC–Ru complex 10 , as well as with the Fischer carbene 7 . The surprising non‐metathetical behavior of the Grubbs’ first‐generation catalyst in this multifaceted process is highlighted. Copyright © 2014 John Wiley & Sons, Ltd.     

Highly efficient chiral copper Schiff-base catalyst for asymmetric cyclopropanation of 2,5-dimethyl-2,4-hexadiene

A remarkable increase in catalytic activity is found for the asymmetric cyclopropanation of 2,5-dimethyl-2,4-hexadiene with diazoacetate by use of the chiral copper Schiff-base complexes, which are derived from substituted salicylaldehydes, chiral aminoalcohols, and copper acetate monohydrate. Furthermore, a combination of a chiral copper Schiff-base with a Lewis acid showed an increase in yield (up to 90%) and in enantioselectivity (up to 90% ee) for the asymmetric cyclopropanation of the diene with t-butyl diazoacetate at 20 °C.     

Z‐bpy,a New C2‐Symmetric Bipyridine Ligand and Its Application in Enantioselective Copper(I)‐Catalyzed Cyclopropanation of Olefins

A rigid C₂‐symmetric chiral bipyridine ligand Z‐bpy with a triptycene‐like backbone was designed and synthesized from simple chemicals in a scalable route. Using this new ligand, copper(I) catalyzed cyclopropanation of styrenes with commercial ethyl diazoacetate produced various corresponding cyclopropanes in high yields, diastereoselectivity and enantioselectivity up to 97% ee.     

Enantio‐ and Diastereoselective Cyclopropanation of 1‐Alkenylboronates: Synthesis of 1‐Boryl‐2,3‐Disubstituted Cyclopropanes

A novel, highly enantio‐ and diastereoselective synthesis of 1‐boryl‐2,3‐disubstituted cyclopropanes has been developed by means of the cyclopropanation of alkenylboronates with ethyl diazoacetate in the presence of catalytic amounts of a chiral copper(I) complex. The products can also be directly accessed from alkynes through an operationally simple, sequential hydroboration–cyclopropanation protocol. The resulting enantioenriched 1‐boryl‐2,3‐disubstituted cyclopropanes are versatile synthetic intermediates that undergo further transformations at the carbon–boron bond.     

Asymmetric Induction of Chiral 1,1''''-Bis(oxazolinyl)ferrocenes as Ligands in Metal-Catalyzed Cyclopropanation and Diels-Alder Reactions

Bis(oxazoline) ligands1 have been successfully used in a variety of metal-catalyzed asymmetric reactions, such as cyclopropanation, allylic oxidation reactions, etc; Chiral ferrocene derivatives2 have also been proved as effective ligands in numerous asymmetric reactions, for example, chiral ferrocenylphosphines exhibited high enantioselectivity for the reduction of olefins, Heck reactions and Aldol reactions of aldehydes. These results stimulated us to study the behaviour the bis(oxazoline) …     

Highly cis-selective Rh(I)-catalyzed cyclopropanation reactions

The performance of recently reported highly cis-diastereoselective Rh(I) cyclopropanation catalysts has been significantly improved by a systematic study of different reaction parameters (catalyst activation, solvent, temperature, stoichiometry). The catalyst efficiency and diastereoselectivity were enhanced by changing the activating agent from AgOTf to NaBArf. With this new system, the Rh(I) catalyst was shown to be a highly efficient and cis-diastereoselective cyclopropanation catalyst in reactions between α-diazoacetates and a range of different alkenes and substituted derivatives. Particularly noteworthy is the remarkable reactivity and cis-diastereoselectivity displayed in the reactions between ethyl diazoacetate and cyclopentene, 2,5-dihydrofuran, and benzofuran, with yields up to 99% and cis-selectivities greater than 99%.     

Enantio- and diastereocontrol in intermolecular cyclopropanation reaction of styrene catalyzed by dirhodium(II) complexes with bulky ortho-metalated aryl phosphines

Enantiomerically pure dirhodium(II) complexes with ortho-metalated p-substituted aryl phosphines have been shown to be enantio- and diastereoselective in the cyclopropanation of styrene by ethyl diazoacetate. Enantioselectivities up to 91% and diastereoselectivities up to 90% are observed for ethyl cis-2-phenylcyclopropanecarboxylate.     

用原位变温19F NMR研究三氟甲磺酸根在苯乙烯不对称环丙烷化反应中的作用

The role of trifluoromethanesulfonate ion (OTf -) in asymmetric cyclopropanation of styrene catalyzed by ruthenium complex of chiral N, P ligand is investigated by in situ variable temperature 19 F NMR. The temperature of NMR experiment varies from 243 K to 283 K. After ethyl diazoacetate and styrene are added into the catalytic system, the process that the OTf - leaves from the central metal is observed from the change of the 19 F NMR spectra. Owing to the weakly coordinating behavior, trifluoromethanesulfonate ion can be easily removed from the central metal and replaced by substrates to form the reactive intermediate during the reaction. So that the catalytic reactivity can be improved greatly when the silver trifluoromethanesulfonate is added to the catalytic system.     

Cu(I) catalysed cyclopropanation with enantiopure scorpionate type ligands derived from (+)-camphor or (-)-menthone

One-pot syntheses of three new enantiopure heteroscorpionate ligands derived from (+)-camphor or (-)-menthone are described. The ligands are obtained by reacting pyrazoles derived from (+)-camphor or (-)-menthone with sodium hydride and thionyl chloride. Subsequent reactions with pyridine and various aldehydes afford the tripod ligands in multi-gram amounts. Especially the menthopyrazole based ligand 6 showed encouraging ee values up to 69% in the Cu(I) catalysed enantioselective cyclopropanation of styrene with ethyl diazoacetate.     

Transition metal-catalyzed cyclopropanation of alkenes in water: catalyst efficiency and in situ generation of the diazo reagent

[reaction: see text] A cyclopropanation reaction involving ethyl diazoacetate and olefins proceeds with surprisingly high efficiency in aqueous media using Rh(II) carboxylates. Nishiyama's Ru(II) Py-box and Katsuki's Co(II) Salen complexes that allow for highly enantioselective cyclopropanations in organic solvents can also be applied to aqueous cyclopropanations with similar results. In situ generation of ethyl diazoacetate and cyclopropanation also proceeds efficiently. A chemoselective O-H insertion is also possible in water when hydrophobic catalysts and alcohols are used.     

The [2 + 1] and [4 + 3] cyclization reactions of fulvenes with Fischer carbene complexes: new access to annulated cyclopentanones

Pentafulvenes are regioselectively cyclopropanated with group 6 Fischer carbene complexes leading to the homofulvene ring with complete endo selectivity. The homofulvene adducts undergo in turn a further cyclopropanation with ethyl diazoacetate or cyclopentannulation with a Fischer alkenyl carbene complex to provide substituted cyclopentanones after ozonolysis of the exocyclic carbon=carbon double bond. Fischer alkynyl carbene complexes also produce the corresponding alkynyl homofulvenes, albeit the exo stereoisomer is in this case exclusively or preferentially formed. Under moderate CO pressure, tungsten alkynyl carbene complexes cycloadd to pentafulvenes in a [4 + 3] fashion, giving rise to bicyclo[3.2.1]octadien-2-ones.     

Highly stereoselective Ru(II)-Pheox catalyzed asymmetric cyclopropanation of terminal olefins with succinimidyl diazoacetate

The Ru(II)-Pheox complex is an efficient catalyst for the intermolecular cyclopropanation of various terminal olefins with succinimidyl diazoacetate. This catalytic system can perform under mild conditions, and the desired cyclopropane products are obtained in high yields with excellent diastereoselectivity and enantioselectivity.     

Transition metal-catalyzed cyclopropanation of alkenes in fluorinated alcohols

The system hexafluoroisopropanol/ethyl diazoacetate/Cu(OTf)₂ is efficient for the cyclopropanation reaction. The process is experimentally simple, and efficient with various olefins in particular terminal, disubstituted double bonds.     

The first immobilization of pyridine-bis(oxazoline) chiral ligands

[formula: see text] A chiral pyridine-bis(oxazoline) ligand, functionalized with a vinyl group in the pyridine ring, can be polymerized with styrene and divinylbenzene to obtain supported chiral ligands. As proof of the usefulness of this supported ligands, the corresponding ruthenium complexes are catalysts for the cyclopropanation reaction of styrene with ethyl diazoacetate with up to 85% ee.     

Catalytic Enantioselective Synthesis of Halocyclopropanes

A catalytic asymmetric synthesis of halocyclopropanes is described. The developed method is based on a carbenoid cyclopropanation of 2‐haloalkenes with tert‐butyl α‐cyano‐α‐diazoacetate using a chiral rhodium catalyst that permits access to a broad range of highly functionalized chiral halocyclopropanes (F, Cl, Br, and I) in good yields, moderate diastereoselectivity, and excellent enantiomeric ratios. The reported methodology represents the first general catalytic enantioselective approach to halocyclopropanes.     

Gold-catalyzed olefin cyclopropanation

The selectivity of the cyclopropanation of olefins with ethyl phenyldiazoacetate has been tested using different gold complexes bearing phosphine, phosphite or N-heterocyclic as ligands. A comparative study with related copper and silver complexes as catalysts is also presented.