Anodic Dehydrogenative Aromatization of Tetrahydrocarbazoles Leading to Carbazoles.

Anodic oxidation-promoted aromatization of 1,2,3,4-tetrahydrocarbazoles was achieved. Nitrogen-protected tetrahydrocarbazoles could be converted to the corresponding carbazoles with the use of bromide as a mediator. LiBr, an inexpensive bromide source, allowed for efficient transformation in the presence of AcOH.

Electrochemical Synthesis of Sultone Derivatives via Dehydrogenative C-O Bond Formation.

Electrochemical dehydrogenative C-O bond formation for the synthesis of sultones was achieved. In the presence of K2CO3 and H2O, constant current electrolysis of [1,1'-biphenyl]-2-sulfonyl chloride afforded an aryl-fused sultone quantitatively. Under the optimized conditions, a variety of sultone derivatives were obtained. Control experiments suggest that the electrochemical oxidation of the sulfonates generated in situ would afford sulfo radical intermediates.

Electrochemical Synthesis of Dibenzothiophenes via Intramolecular C-S Cyclization with a Halogen Mediator.

Electrochemical synthesis of dibenzothiophene derivatives was achieved. Several bis(biaryl) disulfides are efficiently converted to dibenzothiophenes by electrochemical oxidation. The use of Bu4NBr as a halogen mediator was essential, and wide varieties of dibenzothiophene derivatives were obtained in good yields.

Electrochemical hydrogenation of enones using a proton-exchange membrane reactor: selectivity and utility.

Electrochemical hydrogenation of enones using a proton-exchange membrane reactor is described. The reduction of enones proceeded smoothly under mild conditions to afford ketones or alcohols. The reaction occurred chemoselectively with the use of different cathode catalysts (Pd/C or Ir/C).

Application of an Electrochemical Microflow Reactor for Cyanosilylation: Machine Learning-Assisted Exploration of Suitable Reaction Conditions for Semi-Large-Scale Synthesis.

Cyanosilylation of carbonyl compounds provides protected cyanohydrins, which can be converted into many kinds of compounds such as amino alcohols, amides, esters, and carboxylic acids. In particular, the use of trimethylsilyl cyanide as the sole carbon source can avoid the need for more toxic inorganic cyanides. In this paper, we describe an electrochemically initiated cyanosilylation of carbonyl compounds and its application to a microflow reactor. Furthermore, to identify suitable reaction conditions, which reflect considerations beyond simply a high yield, we demonstrate machine learning-assisted optimization. Machine learning can be used to adjust the current and flow rate at the same time and identify the conditions needed to achieve the best productivity.

Cu-Catalyzed Dehydrogenative C-O Cyclization for the Synthesis of Furan-Fused Thienoacenes.

The first Cu-catalyzed dehydrogenative C-O cyclization for the synthesis of furan-fused thienoacenes is described. A variety of heteroacenes including a thieno[3,2-b]furan or a thieno[2,3-b]furan skeleton were synthesized by intramolecular C-H/O-H coupling. The use of a mixed solvent of N-methyl-2-pyrrolidone, ethylene glycol monomethyl ether, and toluene was essential for suppressing side reactions and efficiently promoting the reaction. Double C-O cyclization was also conducted to afford highly π-expanded furan-fused thienoacenes.

Electrosynthesis of Phosphacycles via Dehydrogenative C-P Bond Formation Using DABCO as a Mediator.

The first electrochemical synthesis of diarylphosphole oxides (DPOs) was achieved under mild conditions. The practical protocol employs commercially available and inexpensive DABCO as a hydrogen atom transfer (HAT) mediator, leading to various DPOs in moderate to good yields. This procedure can also be applied to the synthesis of six-membered phosphacycles, such as phenophosphazine derivatives. Mechanistic studies suggested that the reaction proceeds via an electro-generated phosphinyl radical.

Electro-Oxidative Coupling Reactions Leading to π-Conjugated Compounds.

Electrochemical reactions are rapidly gaining attention today as a powerful and environmentally benign reaction processes for organic synthesis. We found that the electro-oxidation of palladium acetate afforded cationic palladium species and thus-generated cationic Pd species were efficient mediators for electro-oxidative coupling reactions. Homo-coupling of arylboronic acids and terminal alkynes proceeded efficiently to afford biaryls and butadiyne, respectively. Cross-coupling reactions between terminal alkynes and arylboronic acids were also achieved with the use of a Ag anode. As an advantage of electrochemical reactions, we developed a sequential reaction system switched between oxidative and neutral conditions by the on/off application of electricity, and several π-extended butadiynes were obtained in one-sequence by the system. Electrochemical intramolecular C-S coupling for the synthesis of thienoacene was also developed. The use of Bu4 NBr as a halogen mediator was essential for the reaction.

Kinetic Resolution of Tertiary Alcohols by Chiral DMAP Derivatives: Enantioselective Access to 3-Hydroxy-3-substituted 2-Oxindoles.

We developed an efficient acylative kinetic resolution of 3-hydroxy-3-substituted 2-oxindoles by a chiral DMAP derivative having a 1,1'-binaphthyl with two tert-alcohols units. A wide range of 3-hydroxy-3-substituted oxindoles having various functional groups were efficiently resolved (14 examples, up to s = 60) in the presence of 1 mol % of catalyst within 3-9 h. Multigram-scale reactions (10 g) also proceeded with a high s-factor (s = 43) within 5 h.

Synthesis, optical and electrochemical properties of 4,4'-bibenzo[c]thiophene derivatives.

We designed and synthesized unsubstituted 4,4'-bibenzo[c]thiophene 4,4'-BBT and its silyl-substituted derivatives 1,1'-Si-4,4'-BBT and 1,1',3,3'-Si-4,4'-BBT with one or two tert-butyldimethylsilyl groups on each thiophene ring, as new π-building blocks in emitters, photosensitizers and semiconductors for organic optoelectronic devices. The characterization of 4,4'-BBT, 1,1'-Si-4,4'-BBT and 1,1',3,3'-Si-4,4'-BBT was successfully determined by FTIR, 1H and 13C NMR measurements, high-resolution mass spectrometry (HRMS) analysis, photoabsorption and fluorescence spectroscopy, cyclic voltammetry (CV) and density functional theory (DFT) calculations. Moreover, a single-crystal X-ray structural analysis was successfully made for 1,1'-Si-4,4'-BBT and 1,1',3,3'-Si-4,4'-BBT. The photoabsorption and fluorescence maxima (λ abs max and λ fl max) of the three 4,4'-bibenzo[c]thiophene derivatives in toluene exhibit bathochromic shifts in the order of 4,4'-BBT (359 nm and 410 nm) < 1,1'-Si-4,4'-BBT (366 nm and 420 nm) < 1,1',3,3'-Si-4,4'-BBT (371 nm and 451 nm). The HOMO and LUMO energy levels rise in the order of 4,4'-BBT (-5.55 eV and -2.39 eV) < 1,1'-Si-4,4'-BBT (-5.45 eV and -2.34 eV) < 1,1',3,3'-Si-4,4'-BBT (-5.34 eV and -2.30 eV), but the rise of the HOMO energy level is larger than that of the LUMO energy level, resulting in the bathochromic shift of the photoabsorption band from 4,4'-BBT to 1,1',3,3'-Si-4,4'-BBT. The fluorescence quantum yields (Φ fl) of 4,4'-BBT, 1,1'-Si-4,4'-BBT and 1,1',3,3'-Si-4,4'-BBT in toluene are 0.41, 0.41 and 0.36, respectively. It is worth mentioning that in the solid state 1,1'-Si-4,4'-BBT and 1,1',3,3'-Si-4,4'-BBT show relatively high Φ fl-solid values of 0.22 and 0.25, respectively, whereas 4,4'-BBT exhibits poor solid-state fluorescence properties (Φ fl-solid < 0.02). This work provides an efficient synthetic method for the 4,4'-bibenzo[c]thiophene derivatives and their photophysical properties in the solution and solid state, electrochemical properties and X-ray crystal structures.

Crystal structure of tris-[4-(naphthalen-1-yl)phen-yl]amine.

In the title mol-ecule, C48H33N, the central N atom shows no pyramidalization, so that the N atom and the three C atoms bound to the N atom lie almost in the same plane. The three para-phenyl-ene rings bonded to the N atom are in a propeller form. All of the naphthalene ring systems are slightly bent. In the crystal, mol-ecules form an inversion dimer, through two pairs of C-H⋯π inter-actions, which further inter-acts with the adjacent dimer via another two pairs of C-H⋯π inter-actions, forming a column structure along the a axis. There are no significant inter-actions between these column structures.

Electrochemical Synthesis of Thienoacene Derivatives: Transition-Metal-Free Dehydrogenative C-S Coupling Promoted by a Halogen Mediator.

The first electrochemical dehydrogenative C-S bond formation leading to thienoacene derivatives is described. Several thienoacene derivatives were synthesized by dehydrogenative C-H/S-H coupling. The addition of n Bu4 NBr, which catalytically promoted the reaction as a halogen mediator, was essential.

Iodide-Mediated or Iodide-Catalyzed Demethylation and Friedel-Crafts C-H Borylative Cyclization Leading to Thiophene-Fused 1,2-Oxaborine Derivatives.

The first synthesis of dithieno-1,2-oxaborine derivatives was achieved via iodide-mediated or iodide-catalyzed demethylation of 3-methoxy-2,2'-bithiophene and subsequent C-H borylation. A wide variety of thiophene-fused oxaborines could be synthesized by the procedure.

Enantioselective Acyl Migration Reactions of Furanyl Carbonates with Chiral DMAP Derivatives.

An efficient enantioselective acyl migration reaction of furanyl carbonates was developed to construct all-carbon quaternary stereogenic centers. In some cases, the reactions required only 0.05 mol % (minimum 500 ppm) of catalyst and showed a high turnover frequency value (TOF; 3640 h-1 ). Multigram-scale reactions (10 grams) also proceeded with high enantioselectivity (>99:1 e.r.) in quantitative yield. The catalyst was robust and easily recovered in 98 % yield. A wide range of functional groups were tolerated (15 examples, >98 % yield, up to >99:1 e.r.), and a variety of optically active 3,3'-disubstituted benzofuranone derivatives, which are useful intermediates for the synthesis of natural products and pharmaceuticals, were efficiently obtained. Control experiments on the catalyst structure (e.g., catalyst 1 a vs. 1 a' and 1 a'') and computational calculations revealed that both the catalytic activity and enantioselectivity should be enhanced by hydrogen bonding between catalyst and substrate. Moreover, this system was applied to the challenging γ-selective acyl migration reaction of furanyl carbonates with high γ-selectivity and high enantioselectivity (α:γ=10:90, 95:5 e.r.).

Synthesis and Properties of Dithieno-Fused 1,4-Azaborine Derivatives.

The first synthesis of dithieno[3,2- b:2',3'- e][1,4]azaborinine (DTAB) derivatives has been achieved by Buchwald-Hartwig coupling and subsequent Friedel-Crafts-type C-H borylation. A facile method for further π-extension of DTAB was also developed via stannylation and subsequent Kosugi-Migita-Stille cross-coupling reaction. The fundamental properties of DTAB derivatives were also investigated.

Stereoselective nucleophilic addition reactions to cyclic N-acyliminium ions using the indirect cation pool method: Elucidation of stereoselectivity by spectroscopic conformational analysis and DFT calculations.

In this study, six-membered N-acyliminium ions were generated by the "indirect cation pool" method and reacted with several nucleophiles. These reactions afforded disubstituted piperidine derivatives with high diastereoselectivities and good to excellent yields. The conformations of the obtained N-acyliminium ions were studied by low temperature NMR analyses and DFT calculations and were found to be consistent with the Steven's hypothesis.

Dynamic Kinetic Resolution of Azlactones by a Chiral N, N-Dimethyl-4-aminopyridine Derivative Containing a 1,1'-Binaphthyl Unit: Importance of Amide Groups.

A dynamic kinetic resolution (DKR) of azlactones in the presence of benzoic acid and a binaphthyl-based N, N-4-dimethylaminopyridine (DMAP) derivative 1i having two amide groups at the 3,3'-positions of a binaphthyl unit is developed. The reaction proceeded smoothly with a wide range of azlactones to provide α-amino acid derivatives with good to high enantiomeric ratios (er's). A multigram-scale reaction (2.5 g) for the DKR of azlactone 2d was also demonstrated, and the resulting product was converted to unnatural α-amino acid 6d'.

Miniaturization and Combinatorial Approach in Organic Electrochemistry.

Recent advances in electro-organic chemistry involving miniaturization, integration, and combinatorial chemistry were reviewed. Microelectrode array technology for site-selective electro-organic reactions and addressable libraries provides a direct and unlabeled method for measuring small-molecule-protein interactions. Electrochemical systems using solid-supported bases and acids ("site separation") can realize electrolysis without the addition of supporting electrolytes. Well-designed "bipolar electrodes" have enabled the production of patterned gradient polymer brushes and microfibers. For the display of combinatorial organic electrochemistry, batch and flow electrolysis systems for the optimization and screening of electro-organic reactions as well as the building of chemical libraries for organic compounds are described.

Desymmetrization of meso-1,2-Diols by a Chiral N,N-4-Dimethylaminopyridine Derivative Containing a 1,1'-Binaphthyl Unit: Importance of the Hydroxy Groups.

We developed an acylative desymmetrization of meso-1,2-diols using a binaphthyl-based N,N-4-dimethylaminopyridine (DMAP) derivative 1h with tert-alcohol substituents. The reaction proceeds with a wide range of acyclic meso-1,2-diols and six-membered-ring meso-1,2-diols to provide a monoacylate selectively with a high enantiomeric ratio (er). Only 0.1 mol % of the catalyst facilitated the reaction within a short reaction time (3 h) to afford enantio-enriched monoacylated products in moderate to good yield. Several control experiments revealed that the tert-alcohol units of catalyst 1h play a significant role in achieving high catalytic activity, chemoselectivity of monoacylation, and enantioselectivity.

Synthesis of 3-Benzo[b]thienyl 3-Thienyl Ether via an Addition-Elimination Reaction and Its Transformation to an Oxygen-Fused Dithiophene Skeleton: Synthesis and Properties of Benzodithienofuran and Its π-Extended Derivatives.

The synthesis of 3-benzo[b]thienyl 3-thienyl ether and its dehydrogenative cyclization leading to benzodithienofuran (BDTF; [1]benzothieno[3,2-b]thieno[2,3-d]furan) are described for the first time. Further transformation of BDTF to more π-extended BDTF derivatives and their fundamental physical properties are also studied.