Ruthenium-catalyzed benzylic substitution of benzyl esters with stabilized carbon nucleophiles.

We have accomplished the ruthenium-catalyzed benzylic substitution of benzyl esters with a stabilized carbon nucleophile. A [Cp*RuCl2]2/picolinic acid catalyst system promoted the reaction of 2-naphthylmethyl-2,3,4,5,6-pentafluorobenzoates with a series of stabilized carbon nucleophiles such as malonates, ß-ketoesters, and diketones to give the corresponding benzylic alkylation products in moderate to high yields. We proposed a plausible reaction mechanism that could involve a (π-benzyl)ruthenium intermediate.

Nickel-Catalyzed Asymmetric Friedel-Crafts Propargylation of 3-Substituted Indoles with Propargylic Carbonates Bearing an Internal Alkyne Group.

The nickel-catalyzed highly enantioselective Friedel-Crafts propargylation of 3-substituted indoles with propargylic carbonates bearing an internal alkyne group was developed. A wide array of the propargylic carbonates as well as 3-substituted indoles can be applicable to the asymmetric nickel catalysis, providing the corresponding chiral C-3 propargylated indolenine derivatives bearing two vicinal chiral centers in up to 89% yield with up to >99% ee and 94:6 dr (24 examples).

Nickel-Catalyzed Hydroarylation of in Situ Generated 1,3-Dienes with Arylboronic Acids Using a Secondary Homoallyl Carbonate as a Surrogate for the 1,3-Diene and Hydride Source.

The nickel-catalyzed hydroarylation of 1,3-dienes with arylboronic acids using a secondary homoallyl carbonate as a surrogate for the 1,3-diene and hydride source has been developed. The synthetic strategy allowed an efficient access to a wide array of hydroarylation products in high yields with high functional group compatibility without the use of an external hydride source. Mechanistic experiments indicated that the alkene-directed oxidative addition and subsequent ß-hydride elimination would be a critical process in this transformation.

Synthesis of substituted benzo[b][1,4]oxazepine derivatives by the reaction of 2-aminophenols with alkynones.

We have developed a novel synthetic method accessing benzo[b][1,4]oxazepines that are one of the rare classes of benzoxazepine derivatives by reaction of 2-aminophenols with alkynones in 1,4-dioxane at 100 °C. A series of benzo[b][1,4]oxazepine derivatives can be prepared by using this synthetic protocol. Mechanistic experiments indicated that the hydroxy proton of the aminophenol could play a crucial role in the formation of an alkynylketimine intermediate that undergoes 7-endo-dig cyclization.

Nickel-Catalyzed Transformation of Alkene-Tethered Oxime Ethers to Nitriles by a Traceless Directing Group Strategy.

Nickel-catalyzed transformation of alkene-tethered oxime ethers to nitriles using a traceless directing group strategy has been developed. A series of alkene-tethered oxime ethers derived from benzaldehyde and cinnamyl aldehyde derivatives were converted into the corresponding benzonitriles and cinnamonitriles in 46-98% yields using the nickel catalyst system. Control experiments showed that the alkene group tethered to an oxygen atom on the oximes via one methylene unit plays a key role as a traceless directing group during the catalysis.

Nickel-Catalyzed Benzylic Substitution of Benzyl Esters with Malonates as a Soft Carbon Nucleophile.

The nickel-catalyzed benzylic substitution of benzyl alcohol derivatives with a soft carbon nucleophile is extremely rare compared to that with a hard carbon nucleophile. We have achieved the nickel-catalyzed benzylic substitution of benzyl esters with malonates as a soft carbon nucleophile. Primary and secondary benzyl 2,3,4,5,6-pentafluorobenzoates as well as a wide variety of malonate derivatives were well tolerated in the nickel-catalyzed reaction, providing the corresponding alkylation products in 46-86% yields (34 examples). Additionally, we propose a possible reaction mechanism that would undergo via the η1- and η3-benzylnickel intermediates.

Synthesis of benzoxazoles via the copper-catalyzed hydroamination of alkynones with 2-aminophenols.

We describe herein the synthetic method to benzoxazole derivatives via the copper-catalyzed hydroamination of alkynones with 2-aminophenols. The method produced a wide variety of functionalized benzoxazole derivatives in good yields. Preliminary mechanistic experiments revealed that the reaction would proceed through the copper-catalyzed hydroamination of alkynones and the sequential intramolecular cyclization of ß-iminoketones/elimination of acetophenone promoted by the copper catalyst.

Nickel-Catalyzed Asymmetric Propargylic Amination of Propargylic Carbonates Bearing an Internal Alkyne Group.

We have achieved the nickel-catalyzed asymmetric propargylic amination of propargylic carbonates bearing an internal alkyne group. A wide variety of propargylic carbonates and N-methylaniline derivatives were tolerated under the reaction conditions, providing the corresponding chiral propargylic amines in up to 97% yield with up to 97% ee.

Iron-Catalyzed Intermolecular Hydrothiolation of Internal Alkynes with Thiosalicylic Acids, and Sequential Intramolecular Cyclization Reaction.

We demonstrate the iron-catalyzed intermolecular coupling of internal alkynes and thiosalicylic acid derivatives. The reaction was effectively catalyzed by the Fe(acac)2/1,10-phenanthroline catalyst in toluene/HFIP (hexafluoroisopropyl alcohol) as the reaction solvent and afforded several types of 1,3-oxathiine derivatives in moderate to high yields through the intermolecular hydrothiolation and sequential intramolecular cyclization.

Ruthenium-catalyzed regioselective allylic amination of 2,3,3-trifluoroallylic carbonates.

We demonstrated the ruthenium-catalyzed allylic amination of 2,3,3-trifluoroallylic carbonates with several types of amines. The reactions proceeded with several types of amines, and succeeded in obtaining polyfluorinated terminal alkenes possessing branched allylic amines as a single regioisomer.

Intramolecular Construction of Trifluoromethyl Group by the Palladium-Catalyzed Alkylation of 2,3,3-Trifluoroallylic Carbonates with Indoles.

The palladium-catalyzed alkylation reaction of 2,3,3-trifluoroallylic carbonates with indoles afforded a trifluoromethyl group possessing 3-substituted indole derivatives. The reaction proceeded via attack of the C-3 carbon of the indoles onto the C-2 position of the allylic moiety and intramolecular construction of the trifluoromethyl group by the intramolecular fluorine atom shift from the C-2 position to the C-3 position of the allyl unit.

Regioselective Construction of α,α-Disubstituted Allylic Amines by the Ruthenium-Catalyzed Allylic Amination of Tertiary Allylic Acetates.

The ruthenium-catalyzed regioselective allylic amination of tertiary allylic acetates with several types of amines has been accomplished. The reaction was effectively catalyzed by Cp*RuCl2/5,5'-dimethyl-2,2'-bipyridine or its related ruthenium catalyst systems, and α,α-disubstituted allylic amines were formed as a single regioisomer in moderate to high yields.

Kinetic Resolution of Racemic and Branched Monosubstituted Allylic Acetates by a Ruthenium-Catalyzed Regioselective Allylic Etherification.

We demonstrated the kinetic resolution of racemic and branched monosubstituted allylic acetates by a ruthenium-catalyzed regioselective allylic etherification. The reaction was effectively catalyzed by the chiral ruthenium catalyst, which was generated by [RuCl2(p-cymene)]2 and (S,S)-iPr-pybox and a catalytic amount of TFA, and both the allylic etherification product and recovered allylic acetate were obtained as an enantiomerically enriched form with up to a 103 s value.

Recent Progress on Nazarov Cyclizations: The Use of Iron Salts as Catalysts in Ionic Liquid Solvent Systems.

Nazarov cyclization is an important and versatile method for the synthesis of five-membered carbocycles, and extensive studies have been conducted to optimize the reaction. Among recent studies, several trends are recognized. One is the combination of different reactions with Nazarov cyclization in a one-pot reaction system which enables the preparation of unique cyclization products. The second is the use of a transition-metal catalyst, though Lewis or Brønsted acids have generally been used for the reaction. The third is the realization of the asymmetric Nazarov cyclization. The fourth is the base-catalyzed Nazarov cyclization. Furthermore, several useful protocols for realizing Nazarov cyclization have also been developed. The recent progress on Nazarov cyclizations is summarized in Section 2. Section 3 is our chronicle in this field. We focused on the use of iron as the catalyst in Nazarov cyclizations and ionic liquids as solvents: Nazarov cyclization of thiophene derivatives using FeCl3 as the catalyst was accomplished and we succeeded in demonstrating the first example of an iron-catalyzed asymmetric Nazarov reaction. We next established Nazarov cyclization of pyrrole or indole derivatives using Fe(ClO4 )3 ·Al2 O3 as the catalyst with high trans selectivities in excellent yields. Since the cyclized product was reacted with a vinyl ketone in the presence of the same iron salt, the system allowed realization of the sequential type of Nazarov/Michael reaction of pyrrole derivatives. Furthermore, we demonstrated the recyclable use of the iron catalyst and obtained the desired Nazarov/Michael reaction products in good yields for five repetitions of the reactions without any addition of the catalyst using an ionic liquid, [bmim][NTf2 ], as the solvent. We expect that the iron-catalyzed Nazarov cyclization, in particular, in an ionic liquid solvent might become a useful method to synthesize functional molecules that include cycloalkene moieties.

Copper-Catalyzed Intermolecular Hydroamination of Internal Alkynes with Anilines and Amines.

The copper-catalyzed regioselective intermolecular hydroamination of the aryl and trifluoromethyl group or electron-withdrawing group substituted internal alkynes with amines has been accomplished. The reaction was effectively catalyzed by the ligand-free Cu(OTf)2 and afforded the intended amine derivatives in good yields after treatment of NaBH3CN.

Palladium-catalyzed enantioselective allylic alkylation of trifluoromethyl group substituted racemic and acyclic unsymmetrical 1,3-disubstituted allylic esters with malonate anions.

We examined the palladium-catalyzed allylic alkylation of trifluoromethyl group-substituted racemic and acyclic unsymmetrical 1,3-disubstituted allylic benzoate with a malonate anion, and succeeded in obtaining an enantiomerically enriched product in high yields with high ee values through the dynamic kinetic asymmetric transformation (DYKAT). The best result was attained by the [Pd(C3H5)(cod)]BF4/(S)-tol-BINAP in the presence of BSA or DMAP as a base.

Palladium-catalyzed amination of 2,3,3-trifluoroallyl esters: synthesis of trifluoromethylenamines via an intramolecular fluorine shift and CF3 group construction.

The palladium-catalyzed reaction of 2,3,3-trifluoroallyl esters with several types of amines afforded trifluoromethylenamines, which were formed by the addition of a nitrogen nucleophile at the C-2 position and the intramolecular construction of the trifluoromethyl group via the fluorine atom shift from the C-2 to the C-3 position.

Enantioselective allylic amination of trifluoromethyl group substituted racemic and unsymmetrical 1,3-disubstituted allylic esters by palladium catalysts.

The palladium-catalyzed regio- and enantioselective allylic amination of trifluoromethyl group substituted racemic and unsymmetrical 1,3-disubstituted allylic esters has been accomplished. The enantioselective formation of the α-type allylic amines was attained by the dynamic kinetic asymmetric transformation (DYKAT).

Ruthenium-catalyzed regio- and enantioselective allylic amination of racemic 1-arylallyl esters.

The regio- and enantioselective allylic amination of racemic monosubstituted allylic esters, such as 1-arylallyl acetates, with cyclic secondary amines has been accomplished. The RuCl3/(S,S)-ip-pybox catalyst system has effectively catalyzed the reaction to afford the enantiomerically enriched branch-type allylic amines with perfect regioselectivity and high enantioselectivity.

Palladium-catalyzed double alkylation of 3-aryl-2-fluoroallyl esters with malonate nucleophiles through the carbon-fluorine bond cleavage.

The alkylation of (Z)-3-aryl-2-fluoroallyl acetate with the malonate anion by the [Pd(C3H5)(cod)]BF4/2,2'-bpy catalyst proceeds through the carbon-fluorine bond cleavage, and 2 equiv of the malonate nucleophile was introduced to the allyl substrate.