Kinetic resolution of 1,1'-binaphthyl-2,2'-diamine derivatives by chiral calcium phosphate-catalyzed acylation

1,1'-Binaphthyl-2,2'-diamine (BINAM) is a useful axially chiral compound. The kinetic resolution of BINAM is one of the most crucial methods for synthesizing chiral BINAM. We have developed a chiral calcium phosphate-catalyzed kinetic resolution of BINAM by utilizing an acylation reaction to produce a mono-amide. The kinetic resolution of BINAM derivatives was achieved by using isobutyric anhydride in the presence of chiral calcium phosphate and 4-morpholinopyridine with up to s = 127. 6,6'-Substituted BINAM derivatives were also applicable for this reaction. The resulting mono-acylated BINAM could be transformed into BINAM by hydrolysis under acidic conditions.

Photoreduction of Trifluoromethyl Group: Lithium Ion Assisted Fluoride-Coupled Electron Transfer from EDA Complex

Photoinduced single-electron reduction is an efficient method for the mono-selective activation of the C-F bond on a trifluoromethyl group to construct a difluoroalkyl group. We have developed an electron-donor-acceptor (EDA) complex mediated single-electron transfer (EDA-SET) of α,α,α-trifluoromethyl arenes in the presence of lithium salt to give α,α-difluoroalkylarenes. The C-F bond reduction was realized by lithium iodide and triethylamine, two common feedstock reagents. Mechanistic studies revealed the generation of a α,α-difluoromethyl radical by single-electron reduction and defluorination, followed by the radical addition to alkenes. Lithium salt interacted with the fluorine atom to promote the photoinduced reduction mediated by the EDA complex. Computational studies indicated that the lithium-assisted defluorination and the single-electron reduction occurred concertedly. We call this phenomenon fluoride-coupled electron transfer (FCET). FCET is a novel approach to C-F bond activation for the synthesis of organofluorine compounds.

Visible-light-driven enantioselective intermolecular [2 + 2] photocyclization utilizing bathochromic excitation mediated by a chiral phosphoric acid

We report herein an enantioselective intermolecular [2 + 2] photocyclization of alkenyl 2-pyrrolyl ketones using the bathochromic shift mediated by a chiral phosphoric acid. This synthetic method provides access to cyclobutanes with up to 98% ee. According to the UV-Vis spectra, the bathochromic effect was observed by mixing alkenyl 2-pyrrolyl ketones and a chiral phosphoric acid. A non-linear correlation was observed between the ee of the catalyst and the ee of the cycloadduct, suggesting that both substrates bind to the chiral phosphoric acid and form a dimer complex before photocycloaddition.

2-Silylated Dihydroquinazolinone as a Photocatalytic Energy Transfer Enabled Radical Hydrosilylation Reagent

The hydrosilylation of alkenes is one of the most important methods for the synthesis of organosilicon compounds. In addition to the platinum-catalyzed hydrosilylation, silyl radical addition reactions are notable as economic reactions. An efficient and widely applicable silyl radical addition reaction was developed by using 2-silylated dihydroquinazolinone derivatives under photocatalytic conditions. Electron-deficient alkenes and styrene derivatives underwent hydrosilylation to give addition products in good to high yields. Mechanistic studies indicated that the photocatalyst functioned not as a photoredox catalyst but as an energy transfer catalyst. DFT calculations clarified that the triplet excited state of 2-silylated dihydroquinazolinone derivatives released a silyl radical through the homolytic cleavage of a carbon-silicon bond, and this was followed by the hydrogen atom transfer pathway, not the redox pathway.

Chiral Phosphoric Acid-Palladium(II) Complex Catalyzed Asymmetric Desymmetrization of Biaryl Compounds by C(sp3)-H Activation

Desymmetrization is an essential method for the synthesis of chiral compounds, particularly chiral biaryls. We have developed an enantioselective synthesis of axially chiral biaryls by desymmetrization using C(sp³)-H activation catalyzed by chiral palladium phosphate. Mechanistic studies show that C-H activation is the rate- and enantiomer-determining step. To the best of our knowledge, this is the first report of asymmetric desymmetrization of axially chiral compounds by C(sp³)-H activation.

Enantioselective Synthesis of an All-Carbon Quaternary Stereocenter by Chiral Brønsted Acid-Catalyzed Friedel-Crafts-Type Reaction between Pyrroles and 3-Indolylmethanols

We have developed a chiral phosphoric acid-catalyzed enantioselective Friedel-Crafts alkylation reaction between pyrroles and indolylmethanols. Wide substrate scope was observed, and a chiral all-carbon quaternary center was constructed at the 3 position of indoles in high yields with high to excellent enantioselectivities (up to 99% ee).

Enantioselective Friedel-Crafts Alkylation Reaction of Pyrroles with N-Unprotected Alkynyl Trifluoromethyl Ketimines

Developed herein is an enantioselective Friedel-Crafts alkylation reaction of N-unprotected alkynyl trifluoromethyl ketimines with pyrroles catalyzed by chiral phosphoric acid to furnish chiral primary α-trifluoromethyl-α-(2-pyrrolyl)propargylamines with high enantioselectivity. Transformation of the alkynyl group of the adducts afforded optically active α-trifluoromethylated amines bearing various substituents such as alkyl, alkenyl, enyne, and triazole without loss of optical purity.

Chiral Calcium Phosphate Catalyzed Enantioselective Synthesis of All-Carbon Quaternary Center by Friedel–Crafts Alkylation Reaction of Pyrroles and Trifluoromethylated Nitrostyrenes

A chiral calcium phosphate-catalyzed enantioselective Friedel–Crafts alkylation reaction of pyrroles and α-trifluoromethyl-β-nitrostyrenes has been developed. Pyrroles bearing an all-carbon quaternary center at 2-position were obtained with high to excellent enantioselectivity. Use of 4,7-dihydroindole as a nucleophile and subsequent oxidation resulted in the formation a 2-substituted indole derivative with excellent enantioselectivity. A 3,4-dihydropyrrolo[1,2-c]pyrimidine derivative was successfully synthesized by reduction followed by benzoylation of the product without loss of enantioselectivity. Application to a 1 mmol scale reaction was successfully achieved.

Visible-Light-Driven C-S Bond Formation Based on Electron Donor-Acceptor Excitation and Hydrogen Atom Transfer Combined System

Developed herein is a visible-light-driven synthesis of sulfides by an electron donor-acceptor/single electron transfer and hydrogen atom transfer combined system without transition metals and strong oxidants. This reaction proceeds through the excitation of an electron donor-acceptor complex between a thiolate and an aryl halide, followed by the hydrogen atom transfer from an alkane to the generated aryl radical.

Catalytic trifluoromethylation of iodoarenes by use of 2-trifluoromethylated benzimidazoline as trifluoromethylating reagent

The trifluoromethylation of iodoarenes was accomplished by use of a 2-trifluoromethylbenzimidazoline derivative as the trifluoromethylating reagent and a catalytic amount of Cu(I) in the presence of 2,2'-bipyridyl as the ligand. Through a mechanistic study, we found that the oxidative addition of the iodoarene to the Cu(I)–CF₃ species is the rate-determining step.

Radical Hydroalkylation and Hydroacylation of Alkenes by the Use of Benzothiazoline under Thermal Conditions

The hydroalkylation and hydroacylation of electron-deficient alkenes proceeded smoothly by using benzothiazoline derivatives as radical-transfer reagents under thermal conditions without light irradiation or any additive. Both benzyl and benzoyl moieties were transferred efficiently.

Supramolecular Photocatalysis by Utilizing the Host-Guest Charge-Transfer Interaction: Visible-Light-Induced Generation of Triplet Anthracenes for [4+2] Cycloaddition Reactions

Supramolecular photocatalysis via charge-transfer excitation of a host-guest complex was developed by use of the macrocyclic boronic ester [2+2]_BTH-F containing highly electron-deficient difluorobenzothiadiazole moieties. In the presence of a catalytic amount of [2+2]_BTH-F , the triplet excited state of anthracene was generated from the charge-transfer excited state of anthracene@[2+2]_BTH-F by visible-light irradiation, and cycloaddition of the excited anthracene with several dienes and alkenes proceeded in a [4+2] manner in high yields.

Benzothiazolines as radical transfer reagents: hydroalkylation and hydroacylation of alkenes by radical generation under photoirradiation conditions

Novel radical transfer reagents under photoirradiation conditions were developed by the use of benzothiazoline derivatives.

Control of the reversibility during boronic ester formation: application to the construction of ferrocene dimers and trimers

Equilibration of boronic esters during boronic ester formation was controlled using protic or aprotic solvents under neutral conditions.