Trimethylsilylcyanation Of Benzaldehyde Research Articles

Family of Well-Defined Chiral-at-Cobalt(III) Complexes as Metal-Templated Hydrogen-Bond-Donor Catalysts: Effect of Chirality at the Metal Center on the Stereochemical Outcome of the Reaction.

A family of well-defined Λ- and Δ-diastereomeric octahedral cationic chiral-at-cobalt complexes were obtained by a simple two-step reaction of (R,R)-1,2-diaminocyclohexane, (R,R)-1,2-diphenylethylenediamine, or (S)-2-(aminomethyl)pyrrolidine and substituted salicylaldehydes with a cobalt(III) salt. It was observed for the first time that the use of an excess of cobalt(III) salt provides both the enantiopure Λ and Δ forms of the corresponding cobalt(III) complexes 1 and 2 in a ratio of diastereomers ranging from 1:1.6 to >20:1 (Λ/Δ) and in 31-95% combined yields. The obtained complexes were robust, air- and bench-stable, soluble in most of organic solvents, and insoluble in water. Through variation of the substituents in the phenyl ring of the salicylaldehyde moiety, it was shown that both steric and electronic effects of substituents have a significant impact on the formation of Λ and Δ isomers. Next, the efficacies of the enantiopure metal-templated complexes 1-3 were investigated in three benchmark asymmetric reactions in order to compare their catalytic activity. The chiral cobalt(III) complexes 1-3 were tested as enantioselective hydrogen-bond-donor catalysts in such important reactions as the Michael addition of the O'Donnell substrate to methyl acrylate, epoxidation of chalcone, and trimethylsilylcyanation of benzaldehyde. It was clearly demonstrated that the chirality at the cobalt center has an impact on the stereochemical outcome of the reactions. In particular, the Λ(R,R)-1 and Δ(R,R)-1 complexes acted as "pseudoenantiomeric" catalysts in the epoxidation and trimethylsilylcyanoation reactions, providing both enantiomers of the products with up to 57% enantiomeric excess.

Synthesis, crystal structures, luminescence properties and catalytic application of lanthanide(III) piperidine dithiocarbamate complexes

A series of lanthanide(III) piperidine dithiocarbamate complexes [Ln(Pip-Dtc)3(Phen)] [where Ln=La(III), Ce(III), Pr(III), Nd(III), Sm(III), Gd(III), Tb(III), Dy(III), Er(III); Pip-Dtc=piperidine dithiocarbamate and Phen=1,10-phenanthroline] has been synthesized and structurally characterized by analytical and various spectral techniques such as FT-IR, UV–Vis and 1H NMR. The molecular structure of [Pr(Pip-Dtc)3(Phen)], [Nd(Pip-Dtc)3(Phen)] and [Sm(Pip-Dtc)3(Phen)] complexes were determined by single crystal X-ray diffraction studies. The binding of the Pip-Dtc to the metal center involves two sulfur atoms and Phen through two nitrogen atoms. The metal center is octa-coordinated by three Pip-Dtc and one Phen ligands. The coordination geometry around Ln(III) ion is distorted dodecahedron. The photoluminescence properties of Sm(III), Pr(III), Tb(III), Dy(III) complexes indicated that the emission intensity depend on the nature of the metal ion, ligand and polarity of the medium. These complexes exhibited good to excellent catalytic activity in trimethylsilyl cyanation of benzaldehyde.

Enantioselective trimethylsilylcyanation of benzaldehyde using pyrrolidine-based chiral salen ligands

The in situ formed Ti(IV) complexes of several pyrrolidine-based chiral salen ligands derived from natural (L)-tartaric acid were evaluated as catalysts in the enantioselective trimethylsilylcyanation of benzaldehyde. The catalysts were found to be very active, producing the corresponding product, O-trimethylsilylmandelonitrile, in high yields (>94%) and enantioselectivities of up to 88%.

Mild and Efficient Silylcyanation of Aldehydes Catalyzed by Alkali Metal Fluorides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Mild and Efficient Silylcyanation of Aldehydes Catalyzed by Alkali Metal Fluorides

Cyanohydrins occupy very important role in organic synthesis due to its synthetic versatility that can easily be converted into various polyfuntionalized building blocks, including α-hydroxy compounds and β-amino alcohols. Diorganotin dichloride catalyzes the addition of trimethylsilyl cyanide (TMSCN) to various ketones and aldehydes. A very similar addition to the carbonyl compounds was also found to be catalyzed by copper(II) triflate. Silylcyanation of aromatic ketones is strongly promoted in organic solutions of lithium perchlorate and lithium tetrafluoroborate. Layered zirconium hydrogen phosphate exchanged with potassium ion was found to be an efficient catalyst for silylcyanation of carbonyl compounds. Indium tribromide (InBr3) 6 is a very effective catalyst for the addition of TMSCN to functionalized ketones. Silylylcyanations of ketones were also initiated by N-Oxides/Ti(iPro)4 as the catalysts. Chiral salentitanium complex proved to be an effective catalyst for the enantioselective silylcyanation of aldehydes. A new bifunctional asymmetric catalyst was devised for the silylcyanation of various aldehydes. It is assumed that aluminium would work as a Lewis acid to activate the carbonyl group and the oxygen atom of the phosphine oxide would work as a Lewis base to activate the silylated nucleophiles. The asymmetric addition of TMSCN to aldehydes can be catalyzed by chiral (salen) titanium complexes. Chiral (salen) VO catalyst is found to be more enantioselective than the previous titanium-based systems for the silylcyanation. Various metal salts have been employed as the catalyst for the silylcyanation of carbonyl compounds. Potassium fluoride (KF) has been the catalyst for silylcyanation of 2-octanone with the yield of only 20%. We wish to herein report the example of silylcyanation of aldehydes by using various alkali metal fluorides. Benzaldehyde reacts with TMSCN in CH3CN under the influence of various catalysts (LiF, NaF, KF, and RbF) to give the trimethylsilyl ethers. The result indicates that KF and RbF can be the prominent catalyst for the silylcyanation. Both catalysts require only 2 mol % content for the 100 % conversion of benzaldehyde within 20 min (Table 1). However, RbF gives a little lower yield of silyl ethers (yield: 93%). KF was chosen as the best catalyst for the silylcyanation of various aldehydes (Table 2). Variously substituted benzaldehydes (enrtries 1-6) add to TMSCN to give trimethylsilyl ethers over 95% yield. This indicates that substituent effect is not serious matter for the reactions. Allylic aldehydes (entries 7 and 8) undergo smooth silylcyanation with excellent yield. Cyclic aldehydes (entries 9 and 10) can be easily transformed into the silylethers without difficulty. 2-Furaldehyde, a heterocyclic aldehyde (entry 11) gives corresponding silylether with the high yield. This result indicates that KF can selectively activate the carbonyl function keeping the furan ring intact. The order of catalytic activity of RbF, KF > NaF > LiF could be ascribed to degree of ionization of the salts into the metal cation and fluoride anion. The yield is even better than the silylcyanation catalyzed by zirconium complex. The result is indicated in the Table 2. The possible mechanism for the reaction is as follows (Scheme 1). Fluoride anion (F) adds to TMSCN to give 1. 1 reacts with the aldehyde for formation of 2 that eliminates F to produce 3. A very effective catalytic system for silylcyanation of various kinds of aldehydes have been developed. The mild experimental conditions, extremely short reaction time, inexpensive catalyst and the wide range of substrate Table 1. Trimethylsilylcyanation of Benzaldehyde with Various Catalysts

Application of new unsymmetrical chiral Mn(III), Co(II,III) and Ti(IV) salen complexes in enantioselective catalytic reactions

New unsymmetrical chiral salen complexes were synthesized and the efficiency of Mn(III), Ti(IV), Co(II) and Co(III) type catalysts were examined in the enantioselective epoxidation of styrene and α‐methylstyrene, the trimethylsilylcyanation of benzaldehyde, the borohydride reduction of aromatic ketones and asymmetric hydrolysis of epoxides to diols, respectively. A very high level of enantioselectivity was attainable over the unsymmetrical chiral salen complexes prepared mainly from salicylaldehyde and 2‐formyl‐4,6‐di‐tert‐butylphenol derivatives. Enantiomeric excess of the corresponding reaction product obtained using unsymmetrical chiral salen catalysts was generally higher than that over conventional symmetric chiral salen catalysts.

(S)-3,3-dimethyl-1,2,4-butanetriol as ligand for titanium catalysed asymmetric silylcyanation

Trimethylsilylcyanation of benzaldehyde was effected in up to 76% e.e. using a catalyst prepared from the triol obtained by reduction of D-Pantolactone and titanium isopropoxide.

Enantioselective trimethylsilylcyanation of some aldehydes catalysed by titanium alkoxide–chiral dialkyl tartrate complexes

Highly enantioselective trimethylsilylcyanation of various aldehydes with trimethylsilyl cyanide has been achieved with a modified Sharpless catalyst, consisting of titanium tetraisopropoxide [Ti(OPri)4] and chiral diisopropyl tartrate (DIPT). Asymmetric amplification was also observed in the trimethylsilylcyanation of benzaldehyde with a catalyst composed of Ti(OPri)4 and partially resolved DIPT.