Allylic alkylations catalyzed by the couple palladium complexes-alumina

Using both palladium complexes and alumina, nucleophilic substitution of allyl acetate by various nucleophiles (pKa = 5–13) are realized with good yields at room temperature without preformation of the corresponding carbanions.     

Synthesis of heteroarylidene malonate derived bis(thiazolines) and their application in the catalyzed Friedel–Crafts reaction

A series of novel heteroarylidene malonate derived bis(thiazoline) ligands 1 and 2 were synthesized and applied to a Friedel-Crafts reaction between indole and alkylidene malonate. The Cu(OTf)₂ complex of ligand 2b bearing a benzyl group afforded moderate to excellent enantioselectivity for the adducts (up to >99% ee).     

Enantioselective Friedel-Crafts alkylations catalyzed by bis(oxazolinyl)pyridine-scandium(III) triflate complexes

The enantioselective Friedel-Crafts addition of a variety of indoles catalyzed by bis(oxazolinyl)pyridine-scandium(III) triflate complexes (Sc(III)-pybox) was accomplished utilizing a series of beta-substituted alpha,beta-unsaturated phosphonates and alpha,beta-unsaturated 2-acyl imidazoles. The acyl phosphonate products were efficiently transformed into esters and amides, whereas the acyl imidazole adducts were converted to a broader spectrum of functionalities such as esters, amides, carboxylic acids, ketones, and aldehydes. The sense of stereoinduction and level of enantioselectivity were found to be functions of the size of the substrate employed, the substitution on the ligand, and the catalyst loading. Molecular modeling of the catalyst with the bound substrates was performed based on the crystal structures of the catalyst complexes and the sense of stereoinduction observed in the addition reaction. Nonlinear effects over a range of catalyst concentrations implicate a mononuclear complex as the active catalyst.     

Enantioselective indole Friedel--Crafts alkylations catalyzed by bis(oxazolinyl)pyridine-scandium(III) triflate complexes

A highly enantioselective Friedel-Crafts alkylation of electron-rich aromatic nucleophiles catalyzed by scandium(III) triflate-pyridyl(bis)oxazoline complexes has been accomplished. The reaction involves alpha,beta-unsaturated acyl phosphonates as electrophiles and primarily substituted indoles as nucleophiles. The reactive acyl phosphonate product is converted to the corresponding ester or amide in good overall yield by adding an alcohol or amine directly to the reaction mixture.     

New palladium-bis(oxazoline)-phosphine complexes: synthesis,characterization and catalytic application in alkoxycarbonylation of alkynes

New cationic palladium-bis(oxazoline)-phosphine (Pd-BOX-PR₃) complexes (Pd-BOX-B and Pd-BOX-C) have been synthesized and characterized using ¹H, ¹³C and ³¹P NMR, FTIR spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The new complexes were used as catalysts in the alkoxycarbonylation of alkynes with various alcohols as nucleophiles. The carbonylation has produced the gem-α,β-unsaturated ester isomer (3) in high regioselectivity and excellent yields. The catalyst systems have been optimized by screening the type of palladium complexes and also by varying the reaction parameters including the reaction time, solvent, and temperature. A mechanism of the catalytic cycle based on a N-protonated palladium bis(oxazoline) phosphine active species was proposed for the alkoxycarbonylation reaction.     

Oxaziridine-mediated enantioselective aminohydroxylation of styrenes catalyzed by copper(II) bis(oxazoline) complexes

We report an oxaziridine-mediated enantioselective aminohydroxylation of olefins catalyzed by a chiral copper(II) bis(oxazoline) complex. A variety of styrenic olefins undergo efficient aminohydroxylation with excellent regioselectivity and synthetically useful levels of enantioselectivity (up to 84% ee). The reaction can be conducted on multi-gram scale with as little as 2 mol % of the copper(II) catalyst. Hydrolysis of the resulting 1,3-oxazolines under acidic conditions produces N-sulfonyl amino alcohols that can be purified by recrystallization to afford very high levels of enantioselectivity.     

Asymmetric Friedel-Crafts alkylations of indoles with nitroalkenes catalyzed by Zn(II)-bisoxazoline complexes

[reaction: see text] A novel asymmetric Friedel-Crafts alkylation of indoles with nitroalkenes catalyzed by Zn(II)-bisoxazoline complexes has been developed. The nitroalkylated indoles are synthesized in excellent yields and high enantioselectivities (up to 90% ee). The effects of ligand structure, metal salt, and solvent on the reaction are discussed. The substrates of the reaction can be aromatic, heteroaromatic, and even aliphatic nitroalkenes. The high reactivity and selectivity of the reaction are presumptively attributed to the activation and asymmetric induction of chiral Lewis acids coordinated by nitroalkene substrates through a 1,3-metal bonding model.     

Allylic alkylation of benzoimidazole catalyzed by palladium complexes

Bis(dibenzylidenacetone)palladium is an efficient and highly selective catalyst for the formation ofN-(2,7-dimethylocta-2,7-dienyl)benzoimidazole in the allylation of benzoimidazole withN-(2,7-dimethylocta-2,7-dienyl)-N-methylpiperidinium iodide in the presence of NaH. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 357–360, February, 1999.     

Enantioselective and diastereoselective Mukaiyama-Michael reactions catalyzed by bis(oxazoline) copper(II) complexes.

The scope of highly enantioselective and diastereoselective Michael additions of enolsilanes to unsaturated imide derivatives has been developed with use of [Cu((S,S)-t-Bu-box)](SbF6)2 (1a) as a Lewis acid catalyst. The products of these additions are useful synthons that contain termini capable of differentiation under mild conditions. Michael acceptor pi-facial selectivity is consistent with two-point binding of the imide substrate and can be viewed as an extension of substrate enantioselection in the corresponding Diels-Alder reactions. A model analogous to the one employed to describe the hetero Diels-Alder reaction is proposed to account for the observed relation between enolsilane geometry and product absolute diastereocontrol. Insights into modes of catalyst inactivation are given, including spectroscopic evidence for inhibition of the catalyst by a dihydropyran intermediate that evolves during the course of the reaction. A procedure is disclosed in which an alcohol additive is used to hydrolyze the inhibiting dihydropyran and afford the desilylated Michael adduct in significantly shortened reaction time.     

Surface-enhanced stereoselectivity in Mukaiyama aldol reactions catalyzed by clay-supported bis(oxazoline)-copper complexes

Surface effects on a laponite-exchanged bis(oxazoline)-copper complex modify the stereochemical course of the Mukaiyama aldol reaction between 2-(trimethylsilyloxy)furan and alpha-ketoesters, leading up to 90% ee (dr 86 : 14) becoming the best overall result obtained for this reaction and significantly improving the homogeneous process.     

Highly enantioselective Friedel-Crafts alkylations of indoles with simple enones catalyzed by zirconium(IV)-BINOL complexes

Complexes of BINOL-based ligands with Zr(OtBu)4 catalyze the Friedel-Crafts alkylation reaction of indoles and pyrrole with nonchelating beta-substituted alpha,beta-enones at room temperature affording the expected products with good yields and ee above 95% in most of the studied examples.     

Asymmetric Friedel-Crafts alkylation of methoxyfuran with nitroalkenes catalyzed by diphenylamine-tethered bis(oxazoline)-Zn(II) complexes

The first catalytic asymmetric Friedel-Crafts reaction of 2-methoxyfuran with nitroalkenes was developed under the catalysis of diphenylamine-tethered bis(oxazoline)-Zn(OTf)2 complexes. The reaction conditions and ligands were optimized, and the scope of the reaction was tested by varying the nitroalkenes. For most of aromatic and heteroaromatic nitroalkenes, good yields and high enantioselectivities (86-96% ee) were obtained. The methoxyfuran group in the product can be transformed to carboxylic acid via oxidative fragmentation with full retention of the configuration.     

Enantioselective Friedel-Crafts alkylations of alpha,beta-unsaturated 2-acyl imidazoles catalyzed by bis(oxazolinyl)pyridine-scandium(III) triflate complexes

An enantioselective Friedel-Crafts alkylation with alpha,beta-unsaturated 2-acyl imidazoles and electron-rich aromatic nucleophiles catalyzed by bis(oxazolinyl)pyridine-scandium(III) triflate complexes has been accomplished. These alpha,beta-unsaturated 2-acyl imidazoles are effective electrophiles for the Friedel-Crafts reaction. The resulting adduct 2-acyl imidazole is easily converted to amides, esters, carboxylic acids, ketones, and aldehydes by methylation and subsequent displacement of the imidazole residue.     

Asymmetric Henry reactions catalyzed by metal complexes of chiral oxazoline based ligands

Chiral oxazolines have been synthesized from norephedrine and pyrrole nitrile or benzoyl chloride and applied to the catalytic asymmetric Henry reactions of p-nitro aldehydes with nitromethane to provide β-hydroxy nitroalkanols in high conversion (up to 92%). The reaction was then optimized in terms of the metal, solvent, temperature, and amount of chiral ligand. The corresponding catalyst with Cu(OTf)₂ and isopropanol as the solvent gave the best enantioselectivities (up to 84% ee) of the corresponding β-nitroalkanol for p-nitrobenzaldehyde.     

Mechanism of aziridination of styrene catalyzed by copper(I) bis(oxazoline)

Experimental studies show that copper complexes can be effectively anchored onto the pores of mesoporous solids, having a good catalytic performance in several reactions, among them the aziridination of olefins and in particular, styrene. In this work, the mechanism of the aziridination of styrene catalyzed by a bis(oxazoline) copper(I) complex was studied in detail by means of density functional theory (DFT) calculations. For such reactions in the homogeneous phase, our calculations revealed a wide diversity of reaction‐pathways, which have not been considered in previous studies, and should be taken into account due to the small energy differences between them. What is more, our results show that there is a strong dependence on the chosen DFT functional. This has profound implications on the way the heterogeneous reaction is studied. © 2013 Wiley Periodicals, Inc.     

Enantioselective cyanosilylation of aldehydes catalyzed by novel camphor derived Schiff bases-titanium(IV) complexes

Five tridentate Schiff bases have been prepared from (1R,2S,3R,4S)-3-amino-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ol and salicylaldehydes. X-ray structure investigation revealed differences in their molecular conformation, and their titanium(IV) complexes have been studied with NMR techniques. Among them the complex with the Schiff base obtained from 2-hydroxy-3-isopropylbenzaldehyde, is the most selective catalyst for the cyanosilylation of aliphatic, alicyclic, aromatic, and heteroaromatic aldehydes. The highest enantioselectivity, >99%, was achieved for the addition of trimethylsilyl cyanide to cinnamaldehyde.     

Asymmetric Michael addition of nitroalkanes to nitroalkenes catalyzed by C2-symmetric tridentate bis(oxazoline) and bis(thiazoline) zinc complexes

The first asymmetric synthesis of 1,3-dinitro compounds through Michael addition of nitroalkanes to nitroalkenes catalyzed by C2-symmetric chiral tridentate bis(oxazoline) and bis(thiazoline) zinc complexes was achieved with high enantioselectivities (up to 95% ee).     

Asymmetric Henry reaction catalyzed by C2-symmetric tridentate bis(oxazoline) and bis(thiazoline) complexes: metal-controlled reversal of enantioselectivity

[reaction: see text] C(2)-symmetric tridentate bis(oxazoline) and bis(thiazoline) ligands with a diphenylamine backbone have been investigated in the catalytic asymmetric Henry reaction of alpha-keto esters with different Lewis acids. Their Cu(OTf)(2) complexes furnished S enantiomers, while Et(2)Zn complexes afforded R enantiomers, both of them with higher enantioselectivities (up to 85% ee). Reversal of enantioselectivity in asymmetric Henry reactions was achieved with the same chiral ligand by changing the Lewis acid center from Cu(II) to Zn(II). The results show that the NH group in C(2)-symmetric tridentate chiral ligands plays a very important role in controlling both the yields and enantiofacial selectivity of the Henry products.