cis-Enhanced cyclopropanation catalysts: reaction chemistry of three isomers of Rh2[N(C6H5)COCH3]4

The catalytic activities of three structural isomers of Rh₂[N(C₆H₅)COCH₃]₄ in cyclopropanation reactions were surveyed. These studies showed cis cyclopropanation selectivity with bulky alkenes for 2,2-cis- and 2,2-trans-Rh₂[N(C₆H₅)COCH₃]₄.     

Application of a chiral copper-1,1-bis{2-[(4S)-tert-butyloxazolinyl]}cyclopropane catalyst for asymmetric cyclopropanation of styrene

The structural effects of the bridge moiety and 5-position on bisoxazoline ligands were studied for the copper-catalyzed asymmetric cyclopropanation of styrene with ethyl diazoacetate. The 1,1-bis{2-[(4S)-tert-butyloxazolinyl]}cyclopropane ligand showed a remarkable enhancement in the stereoselectivities (trans/cis = 84/16, >99.9% ee for the trans product) compared with the previously reported best ligand, 2,2-bis{2-[(4S)-tert-butyloxazolinyl]}propane (trans/cis = 75/25, 99.0% ee for the trans product).     

Guide to enantioselective dirhodium(II)-catalyzed cyclopropanation with aryldiazoacetates

Catalytic enantioselective methods for the generation of cyclopropanes have been of long standing pharmaceutical interest. Chiral dirhodium(II) catalysts prove to be an effective means for the generation of diverse cyclopropane libraries. Rh₂(R-DOSP)₄ is generally the most effective catalyst for asymmetric intermolecular cyclopropanation of methyl aryldiazoacetates with styrene. Rh₂(S-PTAD)₄ provides high levels of enantioinduction with ortho-substituted aryldiazoacetates. The less-established Rh₂(R-BNP)₄ plays a complementary role to Rh₂(R-DOSP)₄ and Rh₂(S-PTAD)₄ in catalyzing highly enantioselective cyclopropanation of 3-methoxy substituted aryldiazoacetates. Substitution on the styrene has only moderate influence on the asymmetric induction of the cyclopropanation.     

Chiral C1-symmetric 2,2′:6′,2′′-terpyridine ligands: Synthesis,characterization, complexation with copper(II), rhodium(III) and ruthenium(II) ions and use of the complexes in catalytic cyclopropanation of styrene

Three new optically pure C₁-terpyridine ligands (L1–3) were prepared and the copper(II) complexes, of formula [Cu(L)Cl₂], the rhodium(III) complexes, of formula [Rh(L)Cl₃], and the ruthenium(II) complexes, of formula cis- or trans-[Ru(L)(X)Cl₂] (X = DMSO or CO), were synthesized. Structures of a chiral C₁-ligand, a copper complex, a rhodium complex and a ruthenium DMSO complex were analysed using X-ray crystal structure analysis. The copper, rhodium and ruthenium complexes were shown to be precursors of catalysts for cyclopropanation. Reaction of [Cu(L)Cl₂], [Rh(L)Cl₃] or cis- or trans-[Ru(L)(X)Cl₂] with AgOTf converted the complex to catalyst, which in the case of trans-[Ru(L)(CO)Cl₂] gave enantioselectivities of up to 67% ee for the cis-isomers of styrene cyclopropanes with t-butyl diazoacetate. Comparisons with C₂-analog of copper, rhodium and ruthenium catalysts were made.     

A positive nonlinear effect in catalytic asymmetric cyclopropanation of styrene with ethyl diazoacetate

The existence of a positive nonlinear effect [(+)-NLE] in the asymmetric cyclopropanation of styrene with ethyl diazoacetate catalysed by a chiral Cu(I)-bisoxazoline complex was observed. This effect can be explained by the possible formation of a catalytically inactive heterochiral meso-complex.     

Substituent effects on rates of rhodium-catalyzed allene cyclopropanation

Rates of cyclopropanation for mono- and disubstituted allenes have been measured relative to standard substrates in reaction with aryldiazoacetate esters catalyzed by Rh₂(S-DOSP)₄. Phenylallene derivatives exhibited a linear correlation of rate with σ⁺ coefficients, indicating a resonance-based effect, though the magnitude of the effect for allenes is less than that reported for other cyclopropanations. Relative reaction rates for aliphatic allenes were found to be similar to those for aryl-substituted allenes, but silicon substitution was found to give a 5- to 14-fold rate increase. The rate enhancement effect for 1-silyl allenes can partially make up for loss of rate and regioselectivity, with 1-trimethylsilyl-1,2-butadiene exhibiting high levels of enantioselectivity and diastereoselectivity in reaction with the chiral catalyst.     

Total syntheses of lindenane-type sesquiterpenoids: (±)-chloranthalactones A, B, F, (±)-9-hydroxy heterogorgiolide, and (±)-shizukanolide E

Chloranthalactones A, B, F, 9-hydroxy heterogorgiolide, and shizukanolide E are a family of natural lindenane-type sesquiterpenoids isolated mainly from chloranthaceae. A general synthetic strategy was accomplished by us for the racemic total syntheses of the five natural products. The key steps included substrate-controlled Matteson epoxidation of ketone and highly diastereoselective intramolecular Hodgson cyclopropanation to construct the challenging cis, trans-3/5/6 tricyclic skeleton, along with a methodology developed for the γ-alkylidenebutenolide ring formation.     

Enantiomerically pure phenanthroline or bipyridine containing macrocycles: a new class of ligands for asymmetric catalysis

New enantiomerically pure phenanthroline- and bipyridine-containing macrocycles have been synthesized by combination of the coordinating unit to inexpensive and readily available chiral templates. The catalytic properties of their Cu(I) complexes have been studied in the cyclopropanation of alkenes as test reaction. A simple structural modification of the chiral cavity allowed us to successfully control the trans or cis diastereoselectivity of the reaction.     

One-step cyclopropanation of alkynes with diiodomethane and triethylaluminum

Cyclopropanation of mono- and dialkyl-substituted alkynes under the action of CH₂I₂ and Et₃Al afforded the corresponding 1-alkyl- and 1,2-dialkyl-substituted 1,2-diethylcyclopropanes in 65—80% yields.     

Pathways of Pd-catalyzed cyclopropanation of tetrahydroindene with diazomethane

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Synthesis of chiral water-soluble metalloporphyrins (Fe, Ru,): new catalysts for asymmetric carbene transfer in water

The reaction of optically active Halterman porphyrin with sulfuric acid (95%) provided the expected water-soluble para-tetrasulfonated porphyrin in 82% yield. The metalloporphyrin complexes were prepared by metal insertion (iron) or direct sulfonation of the chiral ruthenium porphyrin. The asymmetric addition of diazoacetate to styrene to give optically active trans cyclopropyl ester (ee up to 86%) was carried out in water by using chiral iron or ruthenium porphyrins with a possible reuse due to the high solubility and stability in aqueous solution.     

First enantioselective synthesis of salinipostin A,a marine cyclic enol-phosphotriester isolated from Salinispora sp

Salinipostins are cyclic enol-phosphotriesters isolated from a marine-derived Salinispora sp. as antimalarial compounds. Herein, the first enantioselective synthesis of salinipostin A was achieved. Organocatalyst-mediated asymmetric cyclopropanation and regioselective cyclopropane ring opening were the key steps.     

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

A series of chiral C₂-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.     

Structure of a Reactive Gold Carbenoid

A formal gold‐for‐chromium transmetalation allowed the gold carbenoid species [Cy₃PAuCAr₂]NTf₂ ( 11 ) (Ar=pMeOC₆H₄‐) to be obtained in crystalline form. The structure in the solid state suggests that there is only little back donation of electron density from gold to the carbene center of 11 and hence very modest Au? C double‐bond character; rather, it is the organic ligand framework that is responsible for stabilizing this species by resonance delocalization of the accumulated positive charge. Because 11 is capable of cyclopropanating p‐methoxystyrene even at low temperature, the discussion of its structure is deemed relevant for a better understanding of the mechanisms of π‐acid catalysis in general.     

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.     

新的钌环丙烷化催化体系的探索(Ⅱ) 氮膦配体立体化学结构控制顺反比选择性的初步研究

本文研究了一个新的钌催化的苯乙烯环丙烷化反应催化体系。当该催化体系用三氟甲磺酸银预处理后其催化的环丙烷化反应产物的顺反比接近1：1,且顺式产物略微占优。这在环丙烷化反应中是不多见的。我们用分子力学／动力学对该催化体系进行了模拟。结果表明键能并非是决定产物顺反比的主要因素,但是对于非键能来说,由于中间体M1与苯乙烯作用生成顺式产物时的范德华作用非常强,它弥补了由静电能所引起的能量上的不利因素。所以总能量对生成顺式产物较为有利。但是由于生成顺式产物与反式产物的总能量差别不大（2．5kcal.mol^-1),所以环丙烷化产物的顺反比接近1：1。这是氮膦配体立体化学结构控制产物选择性的结果。     

Asymmetric Cyclopropanation of Optically Active Vinyl Sulfoxides: A New Synthetic Approach to Biologically Active Compounds

Abstract

The influence of adjacent substituents on stereochemical course of cyclopropanation of vinyl sulfoxides with stabilized and nonstabilized ylides, as well as dependence on reaction conditions, was investigated. Application of optically active cyclopropanes obtained in the synthesis of conformationally constrained analogs of L-glutamic acid, the useful pharmacological tools in investigation of excitatory amino acid receptors, is presented.     

Immobilization of Pd（Ⅱ）Catalysts for Cyclopropanation in Ionic Liquid

Cyclopropanation of styrene with ethyl diazoacetate catalyzed by Pd(Ⅱ） in ionic liquid [omim][BF4] was investigated.Palladium catalysts can be effectively immobilized in ionic liquid.The catalysts PdCl2 and cyclopalladated complex 2 contained in ionic liquid could be recycled for 6 and 7 times,respectively,without losing the efficiency.     

How Does Electrostatic Activation Control Iminium‐Catalyzed Cyclopropanations?

Prediction of lg k = s ( N + E ) verified : In contrast to previous statements, ordinary α,β‐unsaturated iminium ions do react with sulfur ylides. Electrostatic interactions accelerate the reactions by a factor of more than 10⁵ and are responsible for the high stereoselectivity.