Synthesis of Branch-Type 3-Allylindoles from N-Alkyl-N-cinnamyl-2-ethynylaniline Derivatives Using π-Allylpalladium Chloride Complex as a Catalyst.

The reaction of N-alkyl-N-cinnamyl-2-ethynylaniline derivatives 1 via annulation and aza-Claisen-type rearrangement easily afforded corresponding branch-type 3-allylindoles 2 with high regioselectivities in good yields using π-allylpalladium chloride complex as a catalyst.

Wavily Curved Perylene Diimides: Synthesis, Characterization, and Photovoltaic Properties.

Solubility enhancement is a key issue for developing the perylene diimide-based functional materials. Introduction of curved structure proved an effective solubilizing method without employing steric repulsion. In this work, wavily curved perylene diimides were developed as a new family of highly soluble curved perylene diimides. Moreover, their conformational dynamics, aggregating properties, electronic properties, and photovoltaic performances were thoroughly examined in comparison to the previously reported isomer exhibiting an arched curvature. The waved isomer demonstrated heightened rigidity and a greater propensity for aggregation compared to the arched isomer, likely attributed to its more planar structure. Each benzoxepin unit played a role in cancelling out the curvature on the opposite side. While the difference in the molecular curvature did not cause significant alterations in the photophysical and electron-accepting properties, we identified that the modulation of the curved structure is effective in controlling the morphology of the photoelectric conversion layer.

Formal [3 + 2] Cycloaddition of α-Imino Esters with Azo Compounds: Facile Construction of Pentasubstituted 1,2,4-Triazoline Skeletons.

1,2,4-Triazole and 1,2,4-triazoline are important components of bioactive molecules and catalysts employed in organic synthesis. Therefore, the efficient synthesis of these components has received significant research attention. However, studies on their structural diversity remain lacking. Previously, we developed chiral phase-transfer-catalyzed asymmetric reactions of α-imino carbonyl compounds with α,ß-unsaturated carbonyl compounds and haloalkanes. In this study, we demonstrate the formal [3 + 2] cycloaddition reaction of α-imino esters with azo compounds under Brønsted base catalysis, resulting in the corresponding 1,2,4-triazolines in high yields. The results revealed that a wide range of substrates and reactants can be applied, irrespective of their steric and electronic characteristics. The present reaction made the general preparation of 3-aryl pentasubstituted 1,2,4-triazolines possible for the first time. Furthermore, a mechanistic study suggested that the reaction proceeds without isomerization into the aldimine form.

Intramolecular Azo Coupling Reaction of Binaphthyl Compounds: Synthesis of Pyrazole-Containing Helicene-Like Molecules.

A method for accessing pyrazole-containing helicene-like molecules from easily accessible NOBIN derivatives was developed. The reaction proceeded efficiently via diazonium salt intermediates, which provided a series of helicene-like molecular products in yields of 77%-89% regardless of their steric and electronic natures. The photophysical properties of the products were investigated. The 3,3'-disubstituted molecules showed a characteristic blue shift in their emission spectra. Product derivatizations were conducted, and interesting reactivities toward nucleophiles were observed.

Axially chiral N-alkyl-N-cinnamoyl amide type P,olefin ligands for Pd-catalyzed reactions.

We synthesized N-alkyl-N-cinnamoyl amide type phosphine-olefin compounds 1 and found axial chirality in a C(aryl)-N(amide) bond in compounds 1 by HPLC analysis using a chiral stationary phase column. We successfully obtained enantiomeric isomers of 1 and demonstrated the use of (-)-1 for chiral ligands in Pd-catalyzed asymmetric allylic substitution reactions of allylic esters with indoles (up to 97% ee).

Chiral Bromonium Salt (Hypervalent Bromine(III)) with N-Nitrosamine as a Halogen-Bonding Bifunctional Catalyst.

There has been a great focus on halogen-bonding as a unique interaction between electron-deficient halogen atoms with Lewis basic moieties. Although the application of halogen-bonded atoms in organic chemistry has been eagerly researched in these decades, the development of chiral molecules with halogen-bonding functionalities and their utilization in asymmetric catalysis are still in the\ir infancy. We have previously developed chiral halonium salts with amide functionalities, which behaved as excellent catalysts albeit in only two reactions due to the lack of substrate activation abilities. In this manuscript, we have developed chiral halonium salts with an N-nitrosamine moiety and applied them to the Mannich reaction of isatin-derived ketimines with malonic esters. The study focused on our novel bromonium salt catalyst which provided the corresponding products in high yields with up to 80% ee. DFT calculations of the chiral catalyst structure suggested that the high asymmetric induction abilities of this catalyst are due to the Lewis basic role of the N-nitrosamine part. To the best of our knowledge, this is the first catalytic application of N-nitrosamines.

Synthesis of 3-Allylindoles via Annulation of N-Allyl-2-ethynylaniline Derivatives Using a P,Olefin Type Ligand/Pd(0) Catalyst.

Annulation of N-allyl-2-ethynylaniline derivatives easily afforded the corresponding 2-substituted 3-allylindole derivatives in good to excellent yields using P,olefin ligand/palladium catalst systems.

Chiral Symmetry Breaking of Monoacylated Anhydroerythritols and meso-1,2-Diols through Crystallization-Induced Deracemization.

We developed a chiral symmetry breaking method for monoacylated meso diols. The X-ray crystal structure analysis of monoacylated 1,4-anhydroerythritols, meso cyclic diols with a cis configuration, revealed that the O-(p-anisoyl) derivative crystallized as a racemic conglomerate of the P21 21 21 crystal system. It was confirmed that the substrate racemized by intramolecular transfer of the acyl group in the presence of a catalytic amount of base. Evaporating the solvent gradually from the solution or Viedma ripening to promote crystallization-induced deracemization efficiently led to enantiomer crystals. These results provide the first successful example of asymmetric expression and amplification by deracemization of sugar derivatives without an external chemical chiral source. Furthermore, we applied this methodology to acyclic meso-1,2-diols. Three O-monoacylated substrates were successfully deracemized to 99 % ee by Viedma ripening. We also developed asymmetric desymmetrization of meso-1,2-diols by combining acylation and crystallization-induced deracemization.

Cinnamoyl amide type chiral P,olefin ligands for Pd-catalyzed reactions.

We synthesized cinnamoyl amide type chiral P,olefin ligand (S)-4. We successfully obtained separable diastereomers of 4d and demonstrated Pd-catalyzed asymmetric allylic substitution reactions of indoles using (S,aS)-4d as a chiral ligand with high enantioselectivities (up to 98% ee).

Asymmetric Synthesis of Indoline from Achiral Phthalimide Involving Crystallization-Induced Deracemization.

Asymmetric synthesis was performed by combining the photochemical reaction of an achiral substrate followed by crystallization-induced deracemization. The results indicated that a fused indoline produced by photochemical intramolecular δ-hydrogen abstraction and cyclization of N-(5-chloro-2-methylphenyl)phthalimide crystallized as a racemic conglomerate. Since this substrate has an aminal skeleton, racemization involving a ring-opening and ring-closing equilibrium process occurred under suitable conditions. Efficient racemization was observed in acetone containing a catalytic base, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Crystallization-induced dynamic deracemization by Viedma ripening from racemic indoline was performed with an excellent enantioselectivity of 99 % ee. Furthermore, one-pot asymmetric synthesis of the indoline was achieved by the photochemical reaction of achiral phthalimide followed by continuous attrition-enhanced deracemization converging to 99 % ee of enantiomeric crystals. This is the first example of asymmetric expression and amplification by photochemical hydrogen abstraction and crystallization-induced dynamic deracemization.

Influence of N-Substituents on Photovoltaic Properties of Singly Bay-Linked Dimeric Perylene Diimides.

The influence of N-substituents on the photovoltaic properties of singly bay-linked perylene diimides (diPDIs) was systematically investigated to understand the aromatic-aliphatic balance, which is beneficial for achieving high device performance in organic photovoltaic (OPV) systems. The synthesis of various N-substituted diPDIs was successfully achieved using a newly developed one-step procedure, resulting in sufficiently high yields. Detailed investigations of seven variants of diPDIs demonstrated that the primary alkyl substituents, particularly the 2-ethylhexyl group, induce the self-organized growth of thin films with high crystallinity. This is beneficial for enhancing the device performance of bulk heterojunction (BHJ) systems. The results presented herein reveal the important roles of alkyl side chains as hydrophobic solubilizing auxiliaries or primary determinants in the control of the active layer nanomorphology. This offers a valuable guideline that is essential for developing high-performance organic semiconductor materials for future practical applications.

Phase-transfer catalysed asymmetric synthesis of α-chiral tetrasubstituted α-aminothioesters.

Chiral amino thioesters are important scaffolds owing to their widespread use in organic synthesis and biosynthesis. Despite their usefulness, their asymmetric synthesis, especially the catalytic asymmetric synthesis of α-chiral tetrasubstituted α-aminothioesters, is limited, with only one example reported so far. Herein, we report the first phase-transfer catalysed asymmetric synthesis of α-chiral tetrasubstituted α-aminothioesters to afford the corresponding products in up to 81% ee.

Iminophosphorane-mediated regioselective umpolung alkylation reaction of α-iminoesters.

Umpolung reactions of imines, especially the asymmetric reactions, have been extensively studied as they provide access to important chiral amines in an efficient manner. The reactions studied range from simple Michael reactions to several kinds of other reactions such as the aza-benzoin reaction, aza-Stetter reaction, addition with MBH carbonate, and Ir-catalysed allylation. Herein, we report the first umpolung alkylation reaction of α-iminoesters with alkyl halides mediated by iminophosphorane as an organic superbase. The desired products were obtained in up to 82% yield with almost perfect regioselectivities. The key to the regioselectivity of this reaction was the use of 4-trifluoromethyl benzyl imines as a substrate. The products were successfully derivatised into the more functionalised molecules in good yields.

5,11-Diazadibenzo[hi,qr]tetracene: Synthesis, Properties, and Reactivity toward Nucleophilic Reagents.

5,11-Diazadibenzo[hi,qr]tetracene was synthesized as a new nitrogen-substituted polycyclic heteroaromatic compound by Pd-catalyzed cycloisomerization of an alkyne precursor followed by oxidative cyclization with bis(trifluoroacetoxy)iodobenzene. The substitution of imine-type nitrogen atoms significantly enhanced its electron-accepting character and facilitated the direct nucleophilic addition of arylamines under strongly basic conditions to afford the desired amino-substituted products. The introduction of amino groups induced a remarkable red-shift in their absorption spectra; the tetrasubstituted product exhibited intense near-infrared absorbing property. Furthermore, the π-electronic system, which includes a redox-active 1,4-diazabutadiene moiety, underwent reversible interconversion to its corresponding reduced form upon reduction with NaBH4 and aerobic oxidation.

Chirogenesis and Amplification of Molecular Chirality Using Optical Vortices.

The study of chirogenesis of organic molecules is important to elucidate the origin of the homochirality of biomolecules on Earth. Here, we have accomplished chiral symmetry breaking from a racemate using optical vortices with orbital angular momentum and a helical wavefront. We propose a new methodology of asymmetric transformation by the combination of enantioselective crystal nucleation by irradiation with optical vortices and crystallization-induced dynamic optical resolution of conglomerate crystals. Chiral green vortices generated using a spiral phase plate (SPP) with a 532 nm CW-laser were used to irradiate a supersaturated solution of a racemic isoindolinone, leading to crystal nucleation. The handedness of the crystals were controlled by the winding direction of the chiral optical vortices. The molecular chirality of the isoindolinone was then amplified by dynamic crystallization.

Bromonium salts: diaryl-λ3-bromanes as halogen-bonding organocatalysts.

Bromonium salts have been typically but infrequently used in various reactions as good leaving groups or as aryl or vinyl transfer reagents owing to their extremely high nucleofugality. Herein, we report the synthesis of novel, stable bromonium salts and their first catalytic application to the Michael reaction, with excellent product yield (up to 96%).

Curved Perylene Diimides Fused with Seven-Membered Rings.

Curved perylene diimides fused with seven-membered rings have been synthesized using a regioselective bay-functionalization method and Pd-catalyzed intramolecular C-H/C-Br coupling reaction. X-Ray analysis and temperature-dependent NMR spectroscopy revealed the curved molecular structure with a certain degree of conformational flexibility. The curved and expanded π-conjugation altered the electronic properties while retaining the intrinsic properties of the parent perylene diimide. Despite the absence of solubilizing N-substituents, the curved perylene diimides showed sufficient solubility for application in solution-processed organic photovoltaic devices. The devices showed superior performance with a power conversion efficiency of up to 2.76% due to suppressed charge recombination. Our detailed investigations suggest that the introduction of a curved structure enables the removal of the bulky N-substituents, which is an effective way to achieve a thin-film morphology suitable for photoelectric conversion.

Attrition-Enhanced Asymmetric Transformation of Axially Chiral Nicotinamides by Dynamic Chiral Salt Formation.

Atroposelective resolution for axially chiral nicotinamides was achieved by dynamic chiral salt formation with L-DBTA using six types of nicotinamides that could not be optically resolved by the preferential crystallization method. Kinetic studies of their racemization indicated that the chiral conformation was retained for a significant period of time. Two methods of crystallization-induced asymmetric transformation were examined by dynamic diastereomeric salt formation: solvent evaporation from a supersaturated solution, and attrition-enhanced asymmetric transformation. The attrition method was more effective for asymmetric amplification of diastereomeric salts of axially chiral materials. Attrition of equimolar amount of the nicotinamide salts with L-DBTA converged to one diastereomer salts, and the corresponding enantiomers in 87-99 % ee were obtained after the chiral acid was removed. Changing the ratio of two of the nicotinamides with L-DBTA to 1 : 2 inverted the axial chirality.

Regioselective Bay-Functionalization of Perylenes Toward Tailor-Made Synthesis of Acceptor Materials for Organic Photovoltaics.

The development of an efficient synthetic protocol for multiply bay-functionalized perylenes and application of these products to photovoltaics are reported. Tetrabenzyl 1-(4-tert-butylphenoxy)perylene-3,4,9,10-tetracarboxylate underwent a regioselective bromination at the 7-position followed by a further bromination at the 12-position to provide a 7,12-dibromide in high 84% yield. This compound was transformed into a tetrasubstituted C2h -symmetric dibromide by a controlled monoetherification and a final bromination. The synthetic versatility of the new brominated precursors was demonstrated by their application to cross-coupling reactions, cyanation, and derivatization to the corresponding perylene diimide (PDI). Owing to the high solubility and the raised LUMO level, the obtained tetrasubstituted PDI showed significant advantages as an acceptor material for photovoltaic applications, exhibiting a remarkably high open-circuit voltage (VOC ) reaching 1.00 V. The observed high VOC could be understood by reduction of energy offset for charge separation and non-radiative recombination loss.

Absolute Asymmetric Synthesis of an Aspartic Acid Derivative from Prochiral Maleic Acid and Pyridine under Achiral Conditions.

The asymmetric synthesis of an aspartic acid derivative, N-succinopyridine, from prochiral starting materials involving dynamic enantioselective crystallization was accomplished without using any external chiral source. The aza-Michael addition reaction of prochiral maleic acid and pyridine afforded racemic conglomerate N-succinopyridine in water. Continuous stirring of the suspension of the reaction mixture with acetic acid promoted gradual deracemization to afford a crystal with an excellent optical purity of 99 % in 71 % yield.