Cyclopropanation Of Alkenes Research Articles

Control of selectivity in heterogeneous catalysis by tuning nanoparticle properties and reactor residence time

A combination of the advantages of homogeneous and heterogeneous catalysis could enable the development of sustainable catalysts with novel reactivity and selectivity. Although heterogeneous catalysts are often recycled more easily than their homogeneous counterparts, they can be difficult to apply in traditional organic reactions and modification of their properties towards a desired reactivity is, at best, complex. In contrast, tuning the properties of homogeneous catalysts by, for example, modifying the ligands that coordinate a metal centre is better understood. Here, using olefin cyclopropanation reactions catalysed by dendrimer-encapsulated Au nanoclusters as examples, we demonstrate that changing the dendrimer properties allows the catalytic reactivity to be tuned in a similar fashion to ligand modification in a homogeneous catalyst. Furthermore, we show that these heterogeneous catalysts employed in a fixed-bed flow reactor allow fine control over the residence time of the reactants and thus enables the control over product distribution in a way that is not easily available for homogeneous catalysts.

Predicting the Enantioselectivity of the Copper‐Catalysed Cyclopropanation of Alkenes by Using Quantitative Quadrant‐Diagram Representations of the Catalysts

We present a new methodology to predict the enantioselectivity of asymmetric catalysis based on quantitative quadrant-diagram representations of the catalysts and quantitative structure-selectivity relationship (QSSR) modelling. To account for quadrant occupation, we used two types of molecular steric descriptors: the Taft-Charton steric parameter (ν(Charton)) and the distance-weighted volume (V(W) ). By assigning the value of the steric descriptors to each of the positions of the quadrant diagram, we generated the independent variables to build the multidimensional QSSR models. The methodology was applied to predict the enantioselectivity in the cyclopropanation of styrene catalysed by copper complexes. The dataset comprised 30 chiral ligands belonging to four different oxazoline-based ligand families: bis- (Box), azabis- (AzaBox), quinolinyl- (Quinox) and pyridyl-oxazoline (Pyox). In the first-order approximation, we generated QSSR models with good predictive ability (r(2) =0.89 and q(2) =0.88). The derived stereochemical model indicated that placing very large groups at two diagonal quadrants and leaving free the other two might be enough to obtain an enantioselective catalyst. Fitting the data to a higher-order polynomial, which included crossterms between the descriptors of the quadrants, resulted in an improvement of the predicting ability of the QSSR model (r(2) =0.96 and q(2) =0.93). This suggests that the relationship between the steric hindrance and the enantioselectivity is non-linear, and that bulky substituents in diagonal quadrants operate synergistically. We believe that the quantitative quadrant-diagram-based QSSR modelling is a further conceptual tool that can be used to predict the selectivity of chiral catalysts and other aspects of catalytic performance.

Synthesis of functionalized cyclohexenone core of welwitindolinones via rhodium-catalyzed [5 + 1] cycloaddition.

The cyclohexenone core of welwitindolinones was synthesized by a Rh(I)-catalyzed [5 + 1]-cycloaddition of an allenylcyclopropane with CO. A pentasubstituted cyclopropane was prepared successfully by a Rh(II)-catalyzed intramolecular cyclopropanation of alkenes with chlorodiazoacetates.

Gold(I)‐Catalysed Cycloisomerisation of 1,6‐Cyclopropene‐enes

The gold(I)-catalysed cycloisomerisation of appropriately substituted 1,6-cyclopropene-enes proceeds through regioselective electrophilic ring opening of the three-membered ring to generate an alkenyl gold carbenoid that achieves the intramolecular cyclopropanation of the remote olefin. This strategy allows straightforward, highly efficient and diastereoselective access to a variety of substituted 3-oxa- and 3-azabicyclo[4.1.0]heptanes, as well as to bicyclo[4.1.0]heptan-3-ol derivatives. Since the isopropylidene group in the resulting cycloisomerisation products can be subjected to ozonolysis, 3,3-dimethylcyclopropenes behave as interesting surrogates for α-diazoketones.

Olefin Cyclopropanation Catalyzed by Iridium(III) Porphyrin Complexes

Tetratolylporphyrinato (TTP) iridium complexes were shown to be extremely active and robust catalysts for the cyclopropanation of olefins using diazo compounds as carbene sources. Ir(TTP)CH3 (1) catalyzed the cyclopropanation of styrene with ethyl diazoacetate (EDA) at −78 °C and achieved 4.8 × 105 turnovers in three successive reagent additions with no sign of deactivation. High yields and moderate trans selectivities were attained for electron-rich and sterically unhindered substrates. A Hammett ρ+ value of −0.23 was determined by competition experiments with para-substituted styrenes. Furthermore, competitive cyclopropanation of styrene and styrene-d8 with EDA and 1 demonstrated a moderate inverse secondary isotope effect of 0.86 ± 0.03. These data are consistent with a catalytic cycle that proceeds through a metalloporphyrin carbene intermediate. Carbene transfer to olefin substrates appears to be rate limiting, as indicated by kinetic studies. Hexavalent iridium halogenato tetratolylporphyrinato comp...

Enantioselective Preparation of cis-β-Azidocyclopropane Esters by Cyclopropanation of Azido Alkenes Using a Chiral Dirhodium Catalyst

A diastereo- and enantiocontrolled preparation of the conformationally restricted cis-β-azidocyclopropane esters have been developed. The Rh(2)(S-DOSP)(4) was found to be an efficient catalyst in hexane for the cyclopropanation of azido alkenes with diazo esters, and 19 cis-β-azidocyclopropane esters were prepared in excellent yields. The value of the diastereomer ratio was up to 99:1, and the enantiomeric excess was up to 95%. Furthermore, the relative and absolute configuration was confirmed by X-ray analysis.

Intermolecular Metal‐Free Cyclopropanation of Alkenes Using Tosylhydrazones

AbstractWe describe the first general method for the metal‐free cyclopropanation of alkenes by using N‐tosylhydrazones as an in situ source of diazo compounds. This new method works with a wide variety of alkenes (styrene derivatives, dienes, enynes, and electron‐deficient alkenes) by using N‐tosylhydrazones derived from various ketones or aldehydes (aromatic, aliphatic, enones). The reaction is performed with the use of K2CO3 as a base to form the diazo species and is compatible with a wide array of functional groups.

Crystal structure of a chiral binaphthyl porphyrin

Condensation of tetrakis-5,10,15,20-(α,β,α,β-2-aminophenyl)porphyrin atropoisomer with 1,1′-binaphthyl, 2,2′-dimethoxy-3,3′-diacetylchloride afforded the corresponding basket handle porphyrin whose structure has been analyzed by X-ray crystallography. The macrocycle presents a ruffled type plane according to Shelnutt method for classifying and quantifying the out-of-plane and in-plane distortion of a porphyrin. This structure clearly shows the position of the methoxy groups with respect to the center of the porphyrin and their possible role in the enantioselective epoxidation and cyclopropanation of olefins.

Binuclear Copper Complexes and Their Catalytic Evaluation

AbstractTwo binuclear copper complexes [{CuI(L1)}2][OTf]2 (1) and [{CuII(L2)Cl}2] (2) have been synthesized and structurally characterized. The reaction of [{(5,7‐dimethyl‐1,8‐naphthyridin‐2‐yl)amino}carbonyl]ferrocene (L1) with [Cu(CH3CN)4][OTf] in dichloromethane afforded complex 1 in high yield and the dicopper(II) complex 2 was obtained by the overnight treatment of N‐(5,7‐dimethyl‐1,8‐naphthyridin‐2‐yl)‐1‐methylpyrrolidine‐2‐carboxamide (L2H) with [Cu(CH3CN)4][BF4] in dichloromethane. The two copper atoms in complex 1 are bridged by two L1 ligands in a trans disposition; the naphthyridine nitrogen atoms bridge two copper centers and the carbonyl oxygen atoms occupy sites trans to the Cu···Cu vector. The metal···metal distance is 2.4594(6) Å. In contrast, in complex 2, each of the two L2 ligands bind to the two copper atoms through one naphthyridine nitrogen, a deprotonated amide, and a proline nitrogen atom to form an open‐book geometry. Both dicopper complexes have been shown to be excellent catalysts for the cyclopropanation of various olefins with ethyl diazoacetate (EDA), with catalyst 1 found to be marginally superior to 2.

(PhBP3)Cu(PPh3)] as a Surrogate of TpxCuL in Homogeneous Catalysis (PhBP3 = PhB(CH2PPh2)3; Tpx = Hydrotrispyrazolylborate)

The novel complexes [(PhBP3)Cu(L)] (PhBP3 = PhB(CH2PPh2)3, L = PPh3, 1; L = tetrahydrofuran, 2) have been synthesized and spectroscopically and, in the case of 1, structurally characterized. Both complexes undergo dissociation of the PPh3 or THF ligand in solution to deliver the (PhBP3)Cu unit, similar in geometry to and isoelectronic with TpxCu (Tpx = trispyrazolylborate ligand). A complete study of the catalytic properties of 1 has shown that it can be considered as a surrogate of TpxCu. The study includes (a) olefin cyclopropanation, cyclopropenation, aziridination, halocarbon addition, and radical polymerization, (b) X–H (X = O, N) functionalization by carbene insertion, and (c) furan conversion into dihydropyridines. Since the observed activity is quite comparable to that already described for TpxCu complexes, this new catalytic system could become an alternative to the latter.

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.

Novel efficient catalysts based on imine-linked mesoporous polymers for hydrogenation and cyclopropanation reactions

Two imine-linked polymer organic frameworks (POFs) with different geometries (C3v-POF and Th-POF) and mesoporous properties were prepared and proved to be catalyst supports. Due to the greater ability of Th-POF to coordinate metals, Cu- and Ir-coordinated Th-POFs were tested as catalysts. Both act as truly heterogeneous catalysts towards cyclopropanation and hydrogenation of alkenes, respectively. The high surface area and easy accessibility to the catalytic sites make these materials very efficient for heterogeneous catalysis. The stability of the coordinated complexes and the porous frameworks allows several reuses with only a minor loss in catalytic activity.

Stable N‐Heterocyclic Carbene (NHC)–Palladium(0) Complexes as Active Catalysts for Olefin Cyclopropanation Reactions with Ethyl Diazoacetate

The Pd(0) complexes [(NHC)PdL(n)] (NHC=N-heterocyclic carbene ligand; L=styrene for n=2 or PR(3) for n=1) efficiently catalyse olefin cyclopropanation by using ethyl diazoacetate (EDA) as the carbene source with activities that improve on previously described catalytic systems based on this metal. Mechanistic studies have shown that all of these catalyst precursors deliver the same catalytic species in solution, that is, [(IPr)Pd(sty)], a 14e(-) unsaturated intermediate that further reacts with EDA to afford [(IPr)Pd(=CHCO(2)Et)(sty)], from which the cyclopropane is formed.

ChemInform Abstract: Open‐Shell Organometallics: Reactivity at the Ligand

AbstractReview: 109 refs.

Cyclopropanation Reactions Mediated by Group 9 Metal Porphyrin Complexes (Eur. J. Inorg. Chem. 33/2011)

AbstractThe cover picture shows the Monte Eyehorn (2131 m), Italy. The cyclopropanation of olefins mediated by porphyrin complexes of group IX metals has been reviewed, and several methodologies affording cyclopropanes with good diastereo‐ and enantioselectivity have been described. The efficiency of porphyrin complexes to reduce the activation barrier (as symbolically represented in the photo) allows the synthesis of a wide class of compounds bearing a large number of different substituents on the cyclopropane ring. An overview of the mechanistic aspects of these reactions, explored over the years to improve the performance of porphyrin‐catalysed cyclopropanations, has also been provided. Details are presented in the Microreview by E. Gallo et al. on p. 5071 ff.

Investigation of the structure and catalytic activity in olefin cyclopropanation of neutral and cationic dicopper complexes of 3,5-bis(pyridinylimino)benzoic acid

Three neutral and one cationic copper(I) complexes with 3,5-bis(pyridinylimino)benzoic acid are synthesized and characterized in solution and in the solid state by a variety of spectroscopic techniques and X-ray crystallography. The compounds are monomeric in nature possessing two Cu(I) centers each coordinated to one of the two diimine sites of the ligand. The chromophores are either N2PX, where X is a halide (Cl, Br or I) for the neutral or N2P2 for the ionic compounds, respectively. The phosphorus donor is triphenylphosphane. The crystal structures of the isostructural bromido and iodido compounds are solved and discussed. The compounds are tested for their catalytic activity in olefin cyclopropanation reactions by means of ethyl diazoacetate decomposition and prove to be moderately active with the ionic one being the most active and the most promising since for cyclohexene it reveals a considerable diastereoselectivity and a 90:10 exo:endo ratio of the final product.

ChemInform Abstract: Transition Metal‐Catalyzed Cyclopropanation of Alkenes in Fluorinated Alcohols.

AbstractThe use of hexafluoroisopropanol as solvent for the copper‐catalyzed cyclopropanation of alkenes leads to a simplified reaction procedure, an improved selectivity and a decreased amount of catalyst as well as ethyl diazoacetate (II).

ChemInform Abstract: Asymmetric Rh(II)‐Catalyzed Cyclopropanation of Alkenes with Diacceptor Diazo Compounds: p‐Methoxyphenyl Ketone as a General Stereoselectivity Controlling Group.

AbstractThe reaction features the use of p‐methoxyphenyl ketone as a diastereo‐ and enantioselective controlling group for the synthesis of a series of cyclopropanes.

Highly Asymmetric Intramolecular Cyclopropanation of Acceptor-Substituted Diazoacetates by Co(II)-Based Metalloradical Catalysis: Iterative Approach for Development of New-Generation Catalysts

3,5-Di(t)Bu-QingPhyrin, a new D(2)-symmetric chiral porphyrin derived from a chiral cyclopropanecarboxamide containing two contiguous stereocenters, has been developed using an iterative approach based on Co(II)-catalyzed asymmetric cyclopropanation of alkenes. The Co(II) complex of 3,5-Di(t)Bu-QingPhyrin, [Co(P2)], has proved to be a general and effective catalyst for asymmetric intramolecular cyclopropanation of various allylic diazoacetates (especially including those with α-acceptor substituents) in high yields with excellent stereoselectivities. The [Co(P2)]-based intramolecular metalloradical cyclopropanation provides convenient access to densely functionalized 3-oxabicyclo[3.1.0]hexan-2-one derivatives bearing three contiguous quaternary and tertiary chiral centers with high enantiomeric purity.

ChemInform Abstract: Propargyl Alcohols as β‐Oxocarbenoid Precursors for the Ruthenium‐Catalyzed Cyclopropanation of Unactivated Olefins by Redox Isomerization.

AbstractBoth [3.1.0] and [4.1.0] bicyclic ring systems are synthesized by the title reaction with excellent chemoselectivity, high degree of atom economy (no separate carbene precursor formation), and great tolerance toward various functional groups.