Toward a rational design of the assembly structure of polymetallic asymmetric catalysts: design, synthesis, and evaluation of new chiral ligands for catalytic asymmetric cyanation reactions

Synthesis of γ-amino acids via photocatalyzed intermolecular carboimination of alkenes

We report a direct approach to achieve the energy transfer-driven carboimination of alkenes for the synthesis of a diverse collection of valuable γ-amino acids.

Asymmetric Cyanation of Activated Olefins with Ethyl Cyanoformate Catalyzed by Ti(IV)-Catalyst: A Theoretical Study

The reaction mechanism and origin of asymmetric induction for conjugate addition of cyanide to the C=C bond of olefin were investigated at the B3LYP-D3(BJ)/6-31+G**//B3LYP-D3(BJ)/6-31G**(SMD, toluene) theoretical level. The release of HCN from the reaction of ethyl cyanoformate (CNCOOEt) and isopropanol (HOiPr) was catalyzed by cinchona alkaloid catalyst. The cyanation reaction of olefin proceeded through a two-step mechanism, in which the C-C bond construction was followed by H-transfer to generate a cyanide adduct. For non-catalytic reaction, the activation barrier for the rate-determining C-H bond construction step was 34.2 kcal mol−1, via a four-membered transition state. The self-assembly Ti(IV)-catalyst from tetraisopropyl titanate, (R)-3,3′-disubstituted biphenol, and cinchonidine accelerated the addition of cyanide to the C=C double bond by a dual activation process, in which titanium cation acted as a Lewis acid to activate the olefin and HNC was orientated by hydrogen bonding. The steric repulsion between the 9-phenanthryl at the 3,3′-position in the biphenol ligand and the Ph group in olefin raised the Pauli energy (ΔE≠Pauli) of reacting fragments at the re-face attack transition state, leading to the predominant R-product.

Cyano-borrowing reaction: nickel-catalyzed direct conversion of cyanohydrins and aldehydes/ketones to β-cyano ketone

A direct nickel-catalyzed, high atom- and step-economical reaction of cyanohydrins with aldehydes or ketones via an unprecedented “cyano-borrowing reaction” has been developed.

A direct nickel-catalyzed, high atom- and step-economical reaction of cyanohydrins with aldehydes or ketones via an unprecedented “cyano-borrowing reaction” has been developed. Cleavage of the C–CN bond of cyanohydrins followed by aldol condensation and conjugate addition of cyanide to α,β-unsaturated ketones proceeded to deliver a range of racemic β-cyano ketones with good to high yields. The practical procedure with the use of a commercial and less-toxic CN source bodes well for wide application of this protocol.

Recent Advances in Metal-Catalyzed Asymmetric 1,4-Conjugate Addition (ACA) of Nonorganometallic Nucleophiles

The metal-catalyzed asymmetric conjugate addition (ACA) reaction has emerged as a general and powerful approach for the construction of optically active compounds and is among the most significant and useful reactions in synthetic organic chemistry. In recent years, great progress has been made in this area with the use of various chiral metal complexes based on different chiral ligands. This review provides comprehensive and critical information on the enantioselective 1,4-conjugate addition of nonorganometallic (soft) nucleophiles and their importance in synthetic applications. The literature is covered from the last 10 years, and a number of examples from before 2007 are included as background information. The review is divided into multiple parts according to the type of nucleophile involved in the reaction (such as C-, B-, O-, N-, S-, P-, and Si-centered nucleophiles) and metal catalyst systems used.

Catalytic asymmetric synthesis of enantioenriched β-nitronitrile bearing a C-CF3 stereogenic center

CF₃ substituted β-nitronitriles with an all-carbon quaternary stereogenic center have been synthesized via asymmetric cyanation reaction.

Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams

The conjugate addition reaction has been a useful tool in the formation of carbon-carbon bonds. The utility of this reaction has been demonstrated in the synthesis of many natural products, materials, and pharmacological agents. In the last three decades, there has been a significant increase in the development of asymmetric variants of this reaction. Unfortunately, conjugate addition reactions using α,β-unsaturated amides and lactams remain underdeveloped due to their inherently low reactivity. This review highlights the work that has been done on both diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams.

Enantioselective conjugate addition of cyanide to chalcones catalyzed by a magnesium-Py-BINMOL complex

An efficient asymmetric conjugate addition of trimethylsilyl cyanide (TMSCN) to chalcones, catalyzed by bifunctional Py-BINMOL-Mg complex, with moderate to good enantioselectivities and in good yields, has been realized in this work.

The Ti-BINOLate-catalyzed, enantioselective ring-opening of meso-aziridines with amines

The titanium-BINOLate-catalyzed, highly enantioselective ring-opening reaction of meso-aziridines has been developed which furnishes trans-1,2-diamines in typically good yields and excellent enantioselectivities. N-Aryl aziridines attached to a 5- or 6-membered carbocyclic ring are among the best substrates for this process providing the products in up to >99% ee. The chiral catalyst is easily prepared in situ from commercially available components and does not require any laborious ligand synthesis. Structural investigations into the catalyst composition reveal an oligomeric structure of the active Ti-complex.

Catalytic enantioselective construction of beta-quaternary carbons via a conjugate addition of cyanide to beta,beta-disubstituted alpha,beta-unsaturated carbonyl compounds

The first general catalytic enantioselective conjugate addition of cyanide to beta,beta-disubstituted alpha,beta-unsaturated ketones and N-acylpyrroles was developed using a strontium catalyst derived from Sr(O(i)Pr)(2) and new chiral ligand 5. The reaction exhibited excellent enantioselectivity and a wide substrate scope using 0.5-10 mol % catalyst. 1,4-Adducts containing beta-quaternary carbons were exclusively produced over 1,2-adducts. ESI-MS analysis of the strontium catalyst indicated that the active catalyst was a trimetallic Sr/5 = 3:5 complex. The exclusive 1,4-selectivity was partly due to the ability of the strontium complex to promote both a retro-cyanation reaction from the 1,2-adducts and highly enantioselective conjugate cyanation.

Asymmetric cyanation of activated olefins with ethyl cyanoformate catalyzed by a modular titanium catalyst

Asymmetric cyanation of a class of easily available olefins with a favorable cyanide source ethyl cyanoformate (CNCOOEt) was realized by an interesting modular catalyst. High yields and ee values were obtained for a range of substrates under solvent-free and mild reaction conditions. The products obtained could be easily transformed to the enantioenriched useful intermediates 5, 6, and pharmaceutically important gamma-aminobutyric acid 7.

Chiral phosphoric acid-catalyzed desymmetrization of meso-aziridines with functionalized mercaptans

Conditions for the phosphoric acid-catalyzed highly enantioselective ring-opening of meso-aziridines with a series of functionalized aromatic thiol nucleophiles are described. The procedure utilizes commercially available aromatic thiols, a series of meso-aziridines, and a catalytic amount of VAPOL phosphoric acid to explore the substrate scope of this highly enantioselective reaction.

Recent progress in asymmetric bifunctional catalysis using multimetallic systems

The concept of bifunctional catalysis, wherein both partners of a bimolecular reaction are simultaneously activated, is very powerful for designing efficient asymmetric catalysts. Catalytic asymmetric processes are indispensable for producing enantiomerically enriched compounds in modern organic synthesis, providing more economical and environmentally benign results than methods requiring stoichiometric amounts of chiral reagents. Extensive efforts in this field have produced many asymmetric catalysts, and now a number of reactions can be rendered asymmetric. We have focused on the development of asymmetric catalysts that exhibit high activity, selectivity, and broad substrate generality under mild reaction conditions. Asymmetric catalysts based on the concept of bifunctional catalysis have emerged as a particularly effective class, enabling simultaneous activation of multiple reaction components. Compared with conventional catalysts, bifunctional catalysts generally exhibit enhanced catalytic activity and higher levels of stereodifferentiation under milder reaction conditions, attracting much attention as next-generation catalysts for prospective practical applications. In this Account, we describe recent advances in enantioselective catalysis with bifunctional catalysts. Since our identification of heterobimetallic rare earth-alkali metal-BINOL (REMB) complexes, we have developed various types of bifunctional multimetallic catalysts. The REMB catalytic system is effective for catalytic asymmetric Corey-Chaykovsky epoxidation and cyclopropanation. A dinucleating Schiff base has emerged as a suitable multidentate ligand for bimetallic catalysts, promoting catalytic syn-selective nitro-Mannich, anti-selective nitroaldol, and Mannich-type reactions. The sugar-based ligand GluCAPO provides a suitable platform for polymetallic catalysts; structural elucidation revealed that their higher order polymetallic structures are a determining factor for their function in the catalytic asymmetric Strecker reaction. Rational design identified a related ligand, FujiCAPO, which exhibits superior performance in catalytic asymmetric conjugate addition of cyanide to enones and a catalytic asymmetric Diels-Alder-type reaction. The combination of an amide-based ligand with a rare earth metal constitutes a unique catalytic system: the ligand-metal association is in equilibrium because of structural flexibility. These catalytic systems are effective for asymmetric amination of highly coordinative substrate as well as for Mannich-type reaction of alpha-cyanoketones, in which hydrogen bonding cooperatively contributes to substrate activation and stereodifferentiation. Most of the reactions described here generate stereogenic tetrasubstituted carbons or quaternary carbons, noteworthy accomplishments even with modern synthetic methods. Several reactions have been incorporated into the asymmetric synthesis of therapeutics (or their candidate molecules) such as Tamiflu, AS-3201 (ranirestat), GRL-06579A, and ritodrine, illustrating the usefulness of bifunctional asymmetric catalysis.