Enantioselective Three-Component Kabachnik−Fields Reaction Catalyzed by Chiral Scandium(III)−N,N′-Dioxide Complexes

Transition-Metal-Free Addition of Dialkyl Phosphites to Phthalazin-2-ium Bromide: Synthesis of α-Aminophosphonate Analogues

α-Aminophosphonate analogues containing a phthalazine skeleton were efficiently obtained by a new transition-metal-free addition of dialkyl phosphites to phthalazin-2-ium bromide under mild conditions. A mechanistic study using isotope labeling and radical inhibition experiment revealed that the present transformation passes through a nucleophilic addition of dialkyl phosphates, rather than an insertion of P-H to carbenes.

Zirconium-catalyzed asymmetric Kabachnik-Fields reactions of aromatic and aliphatic aldehydes

An effective catalyst has been developed for the three-component reaction of aldehydes, anilines and phosphites in an asymmetric catalytic Kabachnik-Fields reaction to give α-aminophosphonates. A catalyst was sought that would give high asymmetric inductions for aromatic and, and more particularly, for aliphatic aldehydes since there has not previously been an effective catalyst developed for this class of aldehydes. The optimal catalyst is prepared from three equivalents of the 7,7'-di-t-butylVANOL ligand, one equivalent of N-methylimidazole and one equivalent of zirconium tetraisopropoxide. This catalyst was most efficient in the presence of 10 mol% benzoic acid. Optimal conditions for aryl aldehydes required the use of 3,5-diisopropyl-2-hydroxyaniline and gave the aryl α-aminophosphonates in up to 96% yield and 98% ee over 11 different aryl aldehydes. The best aniline for aliphatic aldehydes was found to be 3-t-butyl-2-hydroxyaniline and gave the corresponding phosphonates in up to 83% yield and 97% ee over 18 examples. The asymmetric inductions for aliphatic aldehydes were comparable with those for aromatic aldehydes with a mean induction of 90% ee for the former and 91% ee for the latter. The best method for the liberation of the free amine from the aniline substituted α-aminophosphonates involved oxidation with N-iodosuccinimide.

Enantioselective Reductive Cyanation and Phosphonylation of Secondary Amides by Iridium and Chiral Thiourea Sequential Catalysis

The combination of transition-metal catalysis and organocatalysis increasingly offers chemists opportunities to realize diverse unprecedented chemical transformations. By combining iridium with chiral thiourea catalysis, direct enantioselective reductive cyanation and phosphonylation of secondary amides have been accomplished for the first time for the synthesis of enantioenriched chiral α-aminonitriles and α-aminophosphonates. The protocol is highly efficient and enantioselective, providing a novel route to the synthesis of optically active α-functionalized amines from the simple, readily available feedstocks. In addition, the reactions are scalable and the thiourea catalyst can be recycled and reused.

Chirality-Driven Mode of Binding of α-Aminophosphonic Acid-Based Allosteric Inhibitors of the Human Farnesyl Pyrophosphate Synthase (hFPPS)

Thienopyrimidine-based allosteric inhibitors of the human farnesyl pyrophosphate synthase (hFPPS), characterized by a chiral α-aminophosphonic acid moiety, were synthesized as enantiomerically enriched pairs, and their binding mode was investigated by X-ray crystallography. A general consensus in the binding orientation of all (R)- and (S)-enantiomers was revealed. This finding is a prerequisite for establishing a reliable structure-activity relationship (SAR) model.

Synthesis and structural characterization of homochiral coordination polymers with imidazole-based monocarboxylate ligands

Chiral Na[(S)-L^R] (R = Me, 1a; ⁱPr, 1b; CH₂ⁱPr, 1c, and (S)-^secBu, 1d) and Na[(R)-L^R] (R = Me, 1a') compounds were synthesised following standard procedures. New compounds 1d and 1a' were analytically and spectroscopically characterised. 1a and 1c were structurally identified by single-crystal X-ray diffraction methods as homochiral 2D coordination polymers, {Na(H₂O)[(S)-L^Me]}_n and {Na[(S)-L^CH₂iPr]}_n, respectively. Both (S)-2alkyl,2-(1H-imidazol-1-yl)acetate anions displayed unprecedented coordination modes in these coordination polymers: μ₃κ²OκO' for 1a and μ₄κ²Oκ²O' for 1c. Enantiomeric species 1a', {Na(H₂O)[(R)-L^Me]}_n, showed the same X-ray powder diffractogram (XRPD) as 1a, in agreement with a similar crystal structure. DFT calculations on the [L^R]^- anions confirmed their coordination capabilities as ditopic linkers. In fact, the reaction of Na[L^R] with several metal salts yielded the following coordination polymers: {Ag[(S)-L^Me]}_n, 2a, {Ag[(R)-L^Me]}_n, 2a', {Cu[(S)-L^R]₂}_n (R = Me, 3a; ⁱPr, 3b), {Cu[(R)-L^Me]}_n, 3a', {Zn[(S)-L^R]₂}_n (R = Me, 4a; ⁱPr, 4b; (S)-^secBu, 4d) and {Zn[(R)-L^Me]₂}_n, 4a'. For the known compounds 3a and 4a, this procedure is a new synthetic route that avoided high temperature reaction conditions. New complexes 2, 3a', b, and 4a', b, d were characterised by elemental analysis, infrared and XRPD methods and complex 2a by single-crystal X-ray diffraction. This complex is also a two-dimensional coordination polymer in which the [(S)-L^Me]^- anion acts as a μ₄κN,κ²O,κ²O' bridging ligand. Compounds 1-4a' are the first examples of homochiral coordination polymers with imidazole-monocarboxylate ligands based on non-natural amino acids. Preliminary studies on the metal-catalysed preparation of chiral α-aminophosphonates were carried out but, unfortunately, no enantioselectivity was observed.

Catalytic Asymmetric Inverse-Electron-Demand Hetero-Diels-Alder Reaction of Dioxopyrrolidines with Hetero-Substituted Alkenes

A highly efficient enantioselective inverse-electron-demand hetero-Diels-Alder reaction of dioxopyrrolidines with heterosubstituted alkenes has been realized by using a N, N'-dioxide/Ni(II) complex as the catalyst. A series of chiral bicyclic dihydropyranes were generated in excellent yields, good dr, and excellent ee values. Besides, a catalytic cycle with a possible transition state was proposed.

Enantioselective Hydrophosphonylation of in Situ Generated N-Acyl Ketimines Catalyzed by BINOL-Derived Phosphoric Acid

An efficient route to pharmacologically interesting isoindolinone-based α-amino phosphonates is described via asymmetric hydrophosphonylation of in situ generated ketimines catalyzed by BINOL-derived phosphoric acid. The reaction proceeds smoothly at ambient temperature affording a variety of α-amino phosphonates with a quaternary stereogenic center embedded in isoindolinone motif in high yields with excellent enantiomeric ratios (up to 98.5:1.5 er). Several interesting transformations of the products into valuable synthetic intermediates are also depicted.

An efficient asymmetric hydrophosphonylation of unsaturated amides catalyzed by rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with phenoxy-functionalized chiral prolinols

An asymmetric hydrophosphonylation reaction of diethyl phosphite with α,β-unsaturated amides catalyzed by [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ with H₂Lⁿ ((S)-2,4-R₂-6-[[2-(hydroxydiphenylmethyl)pyrrolidin-1-yl]methyl]phenol) was disclosed.

Synthesis and structural characterization of homochiral 2D coordination polymers of zinc and copper with conformationally flexible ditopic imidazolium-based dicarboxylate ligands

Chiral imidazolium-based dicarboxylate ligands behave as bridging ditopic linkers capable of forming 2D coordination polymers with zinc and copper metals.

2-Oxo promoted hydrophosphonylation & aerobic intramolecular nucleophilic displacement reaction

Highly efficient catalyst free methods for the synthesis of α-hydroxy-β-oxo phosphonates (HOP) and α-oxoesters (OE) have been described for the first time. The existence of a 2-oxo group in α-oxoaldehydes (OA) was a key factor in promoting the reaction of the tervalent phosphite form towards activated aldehydes (OA) in the synthesis of HOP.

Aminocatalytic cross-coupling approach via iminium ions to different C - C Bonds

Given the attractive ability of iminium ions to functionalize molecules directly at ostensibly unreactive positions, the reactivity of iminium ions, in which an α CH2 group is replaced by CO was explored. Background studies on the ability of such iminium cations to promote reactions via an iminium-catalyzed or iminium-equivalent pathway are apparently unavailable. Previously, tandem cross-coupling reactions were reported, in which an iminium ion undergoes nucleophilic 1,2-addition to give a putative three-component intermediate that abstracts a proton in situ and undergoes self-deamination followed by unprecedented DMSO/aerobic oxidation to generate α-ketoamides. However, later it was observed that iminium ions can generate valuable α-ketoamides through simple aerobic oxidation. In all reactions, iminium ions were generated in situ by reaction of 2-oxoaldehydes with secondary amines.

Cinchona alkaloid derivative-catalyzed enantioselective synthesis via a Mannich-type reaction and antifungal activity of β-amino esters bearing benzoheterocycle moieties

An efficient synthesis of highly functionalized chiral β-amino ester derivatives containing benzothiophene and benzothiazole moieties is developed by a Mannich-type reaction using a cinchona alkaloid-derived thiourea catalyst. The desired products were obtained in good yields and high enantioselectivities (~86% yield, >99% ee) using to the optimized reaction conditions. The synthesized compounds were characterized by 1H-NMR, 13C-NMR, IR, and HREI-MS analyses. The bioassays identified that compound 5dr has excellent antifungal activity, with a 60.53% inhibition rate against F. oxysporum, higher than that of the commercial agricultural fungicide hymexazol, whose inhibition rate was 56.12%.

Catalyst-free three-component reaction to synthesize chiral α-amino phosphine oxides

A novel method for high diastereoselective syntheses of chiral α-aminophosphine oxides by a three-component reaction involve a metal-free system was performed.

Chiral α-amino phosphonates via rhodium-catalyzed asymmetric 1,4-addition reactions

A new approach for the preparation of enantioenriched α-amino phosphonates and derivatives is described. Indeed, the rhodium-catalyzed asymmetric 1,4-addition of potassium organotrifluoroborates to dehydroaminophosphonates afforded α-amino phosphonates in good yields and high enantioselectivities (up to 96%) using Difluorphos as a chiral ligand.

Catalytic asymmetric hydrophosphonylation of ketimines

Catalytic asymmetric hydrophosphonylation of aromatic and aliphatic N-thiophosphinoyl ketimines with dialkyl phosphite was efficiently promoted by as little as 0.5 mol% of catalyst loading at ambient temperature. The catalyst can be recovered for repeated use, and facile removal of the thiophosphinoyl group allowed for ready access to the phosphonic acid analogue of enantioenriched α,α-disubstituted α-amino acids.

Highly enantioselective synthesis of 3-amino-2-oxindole derivatives: catalytic asymmetric alpha-amination of 3-substituted 2-oxindoles with a chiral scandium complex

A highly enantioselective alpha-amination of 3-substituted oxindoles with azodicarboxylates catalyzed by a chiral Sc(OTf)(3)/N,N'-dioxide complex (Tf: triflate) has been developed and affords the corresponding 3-amino-2-oxindole derivatives in high yields (up to 98%) with excellent enantioselectivities (up to 99% ee). The procedure is capable of tolerating a relatively wide range of substrates, and excellent results (92-96% ee) can also be obtained, even in the presence of 0.5 mol % of catalyst loading under mild conditions. These results showed the potential value of the catalytic approach. Moreover, with high synthetic versatility, the product could be easily transformed into optically active 3-amino-3-methyloxindole bearing a chiral quaternary stereogenic center.