Shin-ichi Fukuzawa

Copper(I) 1,2,3-Triazol-5-ylidene Complexes as Efficient Catalysts for Click Reactions of Azides with Alkynes

Complexes of copper with 1,4-diphenyl, 1,4-dimesityl, and 1-(2,6-diisopropylphenyl)-4-(3,5-xylyl)-1,2,3-triazol-5-ylidene (abnormal NHC = N-heterocyclic carbene) were prepared by consecutive treatment of the corresponding azolium salts with silver oxide and copper chloride. The new CuCl(aNHC) complexes efficiently catalyzed click reactions of azides with alkynes to give 1,4-substituted 1,2,3-triazoles in excellent yields at room temperature with short reaction times. CuCl(TPh) was particularly effective for the reaction between sterically hindered azides and alkynes.

Highly enantioselective asymmetric 1,3-dipolar cycloaddition of azomethine ylide catalyzed by a copper(I)/ClickFerrophos complex.

A copper(I)/ClickFerrophos complex catalyzed the asymmetric 1,3-dipolar cycloaddition reaction of methyl N-benzylideneglycinate (the source of azomethine ylides) with vinyl sulfone to give the exo-2,4,5-trisubstituted pyrrolidine in good yield with high enantioselectivity (99% ee). The complex also effectively catalyzed reactions of other dipolarophiles such as acrylates, maleate, and maleimides to give the exo-2,4,5-, and 2,3,4,5-substituted pyrrolidine derivatives with high diastereo- and enantioselectivities.

Highly Endo-Selective and Enantioselective 1,3-Dipolar Cycloaddition of Azomethine Ylide with α-Enones Catalyzed by a Silver(I)/ThioClickFerrophos Complex

A silver(I)/ThioClickFerrophos complex catalyzed the highly endo-selective asymmetric 1,3-dipolar cycloaddition reaction of methyl N-benzylideneglycinate (the source of azomethine ylides) with (E)-acyclic alpha-enones having an endo/exo ratio of 90/10 to 99/1. The highly functionalized endo-4-acyl pyrrolidines were obtained in good yields with high enantioselectivities (up to 98% ee). The complex also effectively catalyzed endo-selective reactions with 2-cyclopentenone to give the endo-bicyclic pyrrolidine in high enantioselectivity.

Direct C–H Carboxylation with Carbon Dioxide Using 1,2,3-Triazol-5-ylidene Copper(I) Complexes

1,2,3-Triazol-5-ylidene copper(I) complexes (tzNHC-Cu) efficiently catalyzed the direct C-H carboxylation of benzoxazole and benzothiazole derivatives with CO(2) to give the corresponding esters in excellent yields after treatment with alkyl iodide. The tzNHC copper(I) complex, i.e., [(TPr)CuCl], worked somewhat more effectively than the corresponding imidazol-2-ylidene copper(I) complex [(IPr)CuCl] to give the carboxylation product in higher yields.

Samarium(II) di-iodide induced reductive coupling of α,β-unsaturated esters with carbonyl compounds leading to a facile synthesis of γ-lactone

Samarium(II) di-iodide, which is a strong one-electron transfer reducing agent, is effective for the reductive coupling of α,β-unsaturated esters with carbonyl compounds, whereby substituted γ-lactones can easily be prepared in good to excellent yields under very mild conditions. Two mole equiv. of samarium(II) di-iodide to each mole equiv. of starting substrate always give reasonable yields. The presence of an alcohol is essential in the reaction, complex unidentified products being formed in the absence of an alcohol; t-butyl alcohol gave more satisfactory results than methanol and ethanol. The alcohol acts as a proton donor, the use of MeOD leading to a deuteriated γ-lactone. The reaction is applicable to both aliphatic and aromatic ketones or aldehydes, whereas the electrochemical method is limited to aliphatic substrates. The diastereoselectivity is examined in the reaction of 4-t-butylcyclohexanone with ethyl acrylate; an anti-isomer is produced predominantly (syn :anti= 1 : 9) as the result of selective axial attack. The reaction may proceed by a radical mechanism, and reaction may not involve a samarium ester homoenolate. The reaction is extended to the intramolecular reaction of an α,β-unsaturated keto ester (8-oxonon-2-enoate) leading to the ready synthesis of a bicyclic γ-lactone.

Phosphine-nickel(II), -cobalt(II), -palladium(0) and -palladium(II) complexes as catalysts in cross-coupling reactions of aryl- and alkyl-grignard reagents with organic tellurides

Abstract Some alkyl- and aryl-tellurides react with Grignard reagents (RMgBr; R  aryl and alkyl) in the presence of NiCl 2 (PPh 3 ) 2 , NiCl 2 (Ph 2 PCH 2 CH 2 CH 2 PPh 2 ), or CoCl 2 (PPh 3 ) 2 as catalyst in THF or diethyl ehter as solvent to give the cross-coupling products together with the homo-coupling products of the tellurides in good to moderate yields, with elemental tellurium being formed as a black precipitate. A catalytic reduction-oxidation cycle involving a Ni or Co complex bearing an organotellurium moiety (RTe; R  alkenyl, aryl, and alkyl) is proposed for the reaction. Palladium catalysts such as Pd(PPh 3 ) 4 , PdCl 2 (PPh 3 ) 2 , and PdCl 2 (PhCN) 2 are revaled to be much less effective than the Ni and Co catalysts in both the yield and the stereoselectivity of the product.

Synthesis of chiral diferrocenyl diselenides and their application to asymmetric reactions

Abstract Two optically active diferrocenyl diselenides, each of which possesses two chiral centers, were newly prepared from commercial 1-(dimethylamino)ethylferrocenes and applied to induce highly enantioselective selenoxide elimination producing axially chiral allenecarboxylic esters.

Ni(II)- and Co(II)-phosphine complex catalyzed carboncarbon bond formation between organic tellurides and grignard reagents☆

Abstract Treatment of alkenyl and aryl tellurides with Grignard reagents in the presence of NiCl 2 (PPh 3 ) 2 , NiCl 2 (Ph 2 PCH 2 CH 2 CH 2 PPh 2 ), or CoCl 2 (PPh 3 ) 2 as catalyst affords the cross-coupling products together with the homo-coupling products of the tellurides in good to moderate yields under mild conditions.

Silver/ThioClickFerrophos-catalyzed enantioselective conjugate addition and cycloaddition of glycine imino ester with nitroalkenes.

We applied the combination of AgOAc with ThioClickFerrophos, the chiral ferrocenyl triazole-based P,S-ligand, to the reaction of glycine imino ester with nitroalkenes. The conjugate addition of the imino methyl ester preferentially produced anti-α-imino-γ-nitrobutyrates in good yields with high enantioselectivities (ee) of up to 99% at -25 °C in THF in the presence of triethylamine. Meanwhile, the pyrrolidine cycloadducts were obtained as major products in good yields with high enantioselectivities (up to 96% ee) using tert-butyl imino ester in the absence of triethylamine at room temperature.

Palladium-catalyzed allylic oxidation of olefins by t-butyl hydroperoxide and tellurium(IV) oxide

Abstract Treatment of several cyclic olefins, β-pinene, allylbenzene, and estragole with palladium(II) salt in acetic acid in the presence of t-butyl hydroperoxide and tellurium(IV) oxide afforded mainly the corresponding allylic acetates. The reaction proceeded catalytically with palladium(II) salt, t-BuOOH working as a reoxidizing agent.