Asymmetric Hydrophosphonylation of Aldehydes using aCinchona-Diaminomethylenemalononitrile Organocatalyst

Organocatalyzed Synthesis of γ-Alkenyl Butenolides via Asymmetric Direct Vinylogous Conjugate Addition-Elimination of Substituted Furanone Derivatives to β-Phenylsulfonylenones

A diaminomethylenemalononitrile organocatalyst efficiently promoted the asymmetric direct vinylogous conjugate addition of α-angelica lactone derivatives to β-phenylsulfonylenones, affording the corresponding γ-alkenyl γ-butenolides in high yields with excellent enantioselectivities (up to 97% ee) after the elimination of the phenylsulfonyl group. This study reports the first successful example of a stereoselective reaction using β-phenylsulfonylenone as the direct alkenyl donor.

Ru(II)-Catalyzed Enantioselective Transfer Hydrogenation of α-Ketophosphonates: Straightforward Access to Valuable Chiral α-Hydroxy Phosphonates

Asymmetric transfer hydrogenation (ATH) is arguably one of the most powerful tools for the synthesis of chiral compounds. Despite tremendous advances in this field, the reduction of α-ketophosphonates remains largely unexplored. Herein, we report an efficient Ru-catalyzed ATH on a broad range of α-ketophosphonates. Compared with existing methods, our approach offers as advantages mild conditions, operational simplicity, limited waste generation, broad substrate scope (26 examples), good to excellent yields (75-93%), and excellent levels of stereoinduction (from 90% to >99% ee).

Investigation of the Asymmetric Addition Reactions Induced by Pentacoordinated Hydrospirophosphorane Substrate

Pentacoordinated bisaminoacyl hydrospirophosphoranes were first found to induce the asymmetric addition reactions as a novel chiral organic framework. Asymmetric addition reactions of bisaminoacyl hydrospirophosphoranes with aromatic aldehyde and in situ generated imine were investigated, and the corresponding α-hydroxyspirophosphonates and α-amino spirophosphonates were obtained. The addition reaction of hydrospirophosphoranes with Δ_P configuration showed better stereoselectivity than that with Λ_P configuration, not only for the addition reaction to aromatic aldehyde but also to in situ generated imine. Furthermore, the stereochemical mechanisms of asymmetric addition reactions induced by pentacoordinated hydrospirophosphorane were proposed by ³¹P NMR tracing experiment and X-ray diffraction analysis.

Asymmetric Hydrophosphonylation of α,β-Unsaturated Ketones Catalyzed by Rare-Earth Metal Complexes Bearing Trost Ligands

Chiral dinuclear rare-earth metal complexes RE₂Lⁿ₂ (n = 1, RE = Y(1), Eu(2), Nd(3), La(4), Gd(5); n = 2, RE = Eu(6), Gd(7)) stabilized by the corresponding Trost ligands H₃L¹ or H₃L² (H₃L¹ = (S,S)-2,6-bis[2-(hydroxydiphenylmethyl)pyrrolidin-1-ylmethyl]-4-methylphenol, H₃L² = (S,S)-2,6-bis[2-(hydroxydiphenylmethyl)pyrrolidin-1-ylmethyl]-4-chlorophenol) were prepared and three unknown complexes 5-7 were characterized by X-ray diffraction analysis. The chiral rare-earth metal complexes 1-7 displayed high reactivity in the asymmetric hydrophosphonylation of α,β-unsaturated ketones, and 5 mol % of complex 7 together with 10 mol % of chiral diamine (1S,2S)-1,2-cyclohexanediamine were proved to be the optimal catalyst combination. Various hydrophosphonylation products with excellent yields and high to excellent enantiomeric excess (ee) values were obtained in toluene (up to 99% yield, >99% ee).

Asymmetric Henry reaction of trifluoromethyl enones with nitromethane using a N,N-dibenzyl diaminomethylenemalononitrile organocatalyst

A novel N,N -dibenzyl diaminomethylenemalononitrile organocatalyst efficiently promoted asymmetric Henry reactions of trifluoromethyl enones with nitromethane, affording corresponding highly functionalized products in high yields with excellent enantioselectivities (up to 90% ee). This study is the first to report the successful example of the asymmetric 1,2-additions of nitromethane to trifluoromethyl enones.

[Development of Green Asymmetric Organocatalytic Synthesis]

Organocatalysts, which are less toxic than metal catalysis, as well as inexpensive, environmentally benign, and stable against moisture and oxygen compared to metal-based catalysts, have received considerable attention for being efficient and clean catalysts. With respect to green chemistry, the development of organocatalysis is a significant research subject for a sustainable society. This article reviews studies on the development of novel organocatalysts and the reactions achieved from using them. Focusing on the push-pull ethylene moiety, in which two electron-withdrawing groups (EWGs) were introduced, we proposed that the vinylogous amide proton (N-H) will lead to the design of organocatalysts. We have developed the diaminomethylenemalononitrile (DMM) organocatalysts, which are push-pull ethylenes having two cyano groups as EWGs, and proved that they are effective for highly stereoselective hydrophosphonylation with aldehydes. The catalytic ability of the DMM organocatalyst was demonstrated in the development of the first asymmetric hydrophosphonylation of ketones using organocatalysts. The DMM organocatalyst can be applied to the selective 1,4-addition asymmetric hydrophosphonylation of enones. In addition, we designed and synthesized novel organocatalysts bearing squaramide-sulfonamide motif as multiple hydrogen bond donors. Squaramide-sulfonamide organocatalysts efficiently catalyzed the asymmetric direct vinylogous aldol reactions of furan-2(5H)-one with aldehydes. Successively, we achieved the synthesis of γ,γ-disubstituted-δ-hydroxy-γ-butenolide via asymmetric direct vinylogous aldol reaction of furanone derivatives using the squaramide-sulfonamide organocatalysts.

Enantioselective vinylogous aldol reaction of acylphosphonates with 3-alkylidene oxindoles

A simple strategy for yielding chiral tertiary α-hydroxy phosphonates that integrates two highly biologically relevant scaffolds namely 3-alkylidene-2-oxindoles and phosphonates has been described. The hydrogen bonding ability of the bifunctional thiourea catalyst allows simultaneous dual activation of a vinylogous oxindole nucleophile and an acylphosphonate electrophile, affording hydroxyphosphonato-3-alkylidene-2-oxindoles as aldol adducts in high yields (up to 92%) with excellent stereocontrol (up to 99% ee).

Diaminomethylenemalononitrile as a Chiral Single Hydrogen Bond Catalyst: Application to Enantioselective Conjugate Addition of α-Branched Aldehydes

An improved diaminomethylenemalononitrile organocatalyst, bearing a N,N-disubstituted structure, promoted enantioselective conjugate addition reaction of α-branched aldehydes with vinyl sulfone, affording adducts with excellent enantioselectivities (up to 96% ee). Mechanistic studies revealed that the diaminomethylenemalononitrile motif holds the vinyl sulfone substrate using a single hydrogen bond accompanied by multiple weak interactions, including electrostatic C-H⋅⋅⋅O interactions.

Diaminomethylenemalononitriles and Diaminomethyleneindanediones as Dual Hydrogen Bond Donors for Anion Recognition

Diaminomethylenemalononitriles (DMMs) and diaminomethyleneindanediones (DMIs) are dual H-bond donors that have previously been used as organocatalysts, but their anion binding ability has not been investigated. We report the synthesis of both alkyl- and aryl-substituted DMMs and DMIs, together with a comparison of their anion binding ability with that of the analogous thioureas. The DMMs display affinity for monovalent anions, with similar anion binding affinities observed to that of the thioureas in acetonitrile, albeit with differing trends for the N,N'-dialkyl versus N,N'-diaryl compounds. In contrast, the DMIs do not bind to monovalent anions under similar conditions as a result of conformational locking through the formation of intramolecular H-bonds. This can be overcome upon addition of sulfate ions, and binding of sulfate is enhanced in a more competitive solvent (DMSO).

Optical Resolution of Dimethyl α-Hydroxy-Arylmethylphosphonates via Diastereomer Complex Formation Using Calcium Hydrogen O,O′-Dibenzoyl-(2R,3R)-Tartrate; X-Ray Analysis of the Complexes and Products

Two dimethyl α-hydroxy-arylmethylphosphonates (aryl = Ph and 2-MeOPh) were subjected to optical resolution via diastereomer complex formation applying the acidic calcium salt of O,O′-dibenzoyl-(2R,3R)-tartaric acid as the resolving agent. The dominating diastereomer complexes, whose structure was determined by single crystal X-ray measurements, were obtained in 96% and 68% diastereomer excess values, respectively. After decomposing the diastereomer formations by extraction, and after recrystallizations, the major enantiomer (S and R, respectively) of the α-hydroxyphosphonates were prepared in enantiomeric excess values of 96% and 68%, respectively. The stereostructure of the two α-hydroxy-arylmethylphosphonates was again established by X-ray measurements. Detailed study on the X-ray data allowed valuable conclusions on the nature of the coordination in the complexes (intermolecular interactions), and on the H-bonding.

Resolution of Racemic α-Hydroxyphosphonates: Bi(OTf)3-Catalyzed Stereoselective Esterification of α-Hydroxyphosphonates with (+)-Dibenzoyl-l-tartaric Anhydride

A practical and efficient method has been developed for the preparation of optically active α-hydroxyphosphonates through resolution of the racemates. Treatment of racemic diethyl 1-hydroxy-1-phenylmethylphosphonate (1) with (+)-dibenzoyl-L-tartaric anhydride gave two diastereomeric esters 2 and 3 in the presence of bismuth triflate (15 mol %) in an 86:14 ratio. The two diastereomeric esters were separated by simple column chromatography, and the structure for the major diastereomer was determined by X-ray crystallographic analysis. Simple hydrolysis of the isolated major diastereomer in the usual manner afforded (R)-O,O-diethyl-1-[hydroxyl(phenyl)methyl] phosphonate 1. The advantages of the present method are that the operation is simple and easy to handle, along with rapid and good yield preparations of both enantiomers of the racemic α-phosphonates 1. Diastereoselective reactions of various racemic α-hydroxyphosphonates with d-Bz-L-TA in the presence of Bi(OTf)₃ are also described.

Cinchona-Diaminomethylenemalononitrile Organocatalyst for the Highly Enantioselective Hydrophosphonylation of Ketones and Enones

The use of diaminomethylenemalononitrile (DMM) organocatalyst to promote the challenging 1,2-hydrophosphonylation of simple ketones and enones, which are also called α,β-unsaturated ketones, is proposed and validated. This reaction provided the corresponding chiral α-hydroxy phosphonates in high to excellent yields and with enantioselectivity up to 96% ee.

Organocatalytic, Chemoselective Hydrophosphenylation/oxa-Michael Addition Cascade toward Diastereo- and Enantioenriched 1,3-Dihydroisobenzofuryl Phosphonates

An efficient method for the construction of chiral C-P bond via an enantioselective 1,2-hydrophosphenylation followed by an oxa-Michael addition cascade of ortho-formyl chalcones has been developed. This provides the diastereoenriched ( cis)-1,3-dihydroisobenzofuryl phosphonates with excellent enantioselectivities (up to >99%). The origin of enantio- and diastereoselectivity is induced by using a chiral bifunctional organocatalyst. Further, functionalization to highly enantioselective 3-substituted phthalides has also been demonstrated.

Asymmetric Conjugate Additions of Carbonyl Compounds to Nitroalkenes under Solvent-Free Conditions Using Fluorous Diaminomethylenemalononitrile Organocatalyst

The novel fluorous organocatalyst bearing a diaminomethylenemalononitrile motif is prepared. The fluorous organocatalyst efficiently promotes asymmetric conjugate additions of ketones to nitroalkenes and results in high yields of these addition products with excellent enantioselectivities under solvent-free conditions.

Development of Biologically Active Compounds on the Basis of Phosphonic and Phosphinic Acid Functionalities

Phosphonic and phosphinic acids, especially α-heteroatom-substituted ones, possess unique structural and physical features which enable them to act as hydrotically stable analogs to biological phosphates in biological processes. They also act as mimetics in the transition state of the protease-induced hydrolysis of dipeptides. The first half of this review focuses on selected new synthetic methods developed by our research group for the stereoselective synthesis of α-heteroatom-substituted phosphonic and phosphinic acid derivatives, including modified nucleotide analogs and phosphinyl dipeptide isosteres. In the latter half, this review summarizes the utility of difluoromethylenephosphonic acids and phosphonic acid esters in the development of enzyme inhibitors against protein tyrosine phosphatases, sphingomyelinases, purine nucleoside phosphorylases and thrombin. The enzyme inhibitors developed were used as probes to elucidate signal transductions and the mechanisms of enzyme actions. The findings of the studies are briefly described.

Asymmetric Chlorination of β-Keto Esters Using Diaminomethylenemalononitrile Organocatalyst

Diaminomethylenemalononitrile organocatalysts promote the asymmetric chlorination of simple cyclic β-keto esters such as methyl, ethyl, and benzyl esters of 1-oxo-2,3-dihydro-1H-indene-2-carboxylic acid. This affords the corresponding chiral α-chlorinated carbonyl products in excellent yields with high enantioselectivities.

An Ni–PyBisulidine complex for the asymmetric hydrophosphonylation of aldehydes

A novel Ni–PyBisulidine complex has been developed for the asymmetric hydrophosphonylation of aldehydes.