Cage-Shaped Borate Catalysts Bearing Precisely Controlled Lewis Acidity and Their Application in Glycosylations.

Cage-shaped borates, whose Lewis acidity can be precisely modulated by the structural attributes of the triphenolic ligands, were employed as catalysts for glycosylation. Each cage-shaped borate displayed distinctive reactivity; thus, screening of the borate catalysts enabled controllable activation of glycosyl fluorides under mild conditions. Practical glycosylation was achieved by fine-tuning the Lewis acidity tailored to the substrate reactivity, thereby providing a versatile method applicable to the synthesis of complex glycans.

Selective recognition between aromatics and aliphatics by cage-shaped borates supported by a machine learning approach.

Selective recognition between hydrocarbon moieties is a longstanding issue. Although we developed a π-pocket Lewis acid catalyst with high selectivity for aromatic aldehydes over aliphatic ones, a general strategy for catalyst design remains elusive. As an approach that transfers the molecular recognition based on multiple cooperative non-covalent interactions within the π-pocket to a rational catalyst design, herein, we demonstrate Lewis acid catalysts showing improved selectivity through the support of an ensemble algorithm with random forest, Ada Boost, and XG Boost as a machine learning (ML) approach.

-2,6-Di(isopropyl)phenyl-2-azaphenalenyl radical cations.

-2,6-Di(isopropyl)phenyl-2-azaphenalenyl radical cations were obtained as a dark brown air-sensitive crystalline compound. The high HOMA values and the ACID calculation indicate relatively high aromatic character of a 5,8-di--butyl derivative, and clean generation of a derivative without -butyl groups indicates that the di(isopropyl)phenyl group is sufficient for hampering the formation of the σ-dimer.

Synthesis and Characterization of Dibenzothieno[,]pentalenes Enabling Large Antiaromaticity and Moderate Open-Shell Character through a Small Energy Barrier for Bond-Shift Valence Tautomerization.

Experimental and theoretical rationalization of bond-shift valence tautomerization, characterized by double-well potential surfaces, is one of the most challenging topics of study among the rich electronic properties of antiaromatic molecules. Although the pseudo-Jahn-Teller effect (PJTE) is an essential effect to provide attractive characteristics of 4π systems, an understanding of the structure-property relationship derived from the PJTE for planar 4π electron systems is still in its infancy. Herein, we describe the synthesis and characterization of two regioisomers of the thiophene-fused diareno[,]pentalenes and .

Cage-Shaped Phosphites Having C -Symmetric Chiral Environment: Steric Control of Lewis Basicity and Application as Chiral Ligands in Rhodium-Catalyzed Conjugate Additions.

Designing chiral ligands with an axial symmetry higher than C -rotational symmetry is one of the most crucial approaches to improving enantioselectivity in asymmetric synthesis. Herein, C -symmetric chiral cage-shaped phosphites are reported. Their Lewis basicity and chiral environment are precisely controlled by the tethered group.

Synthesis and Characterization of Hexafluorocyclopentane-Bridged Bisbutatrienes as Models for Longer Cumulenes: Various Transformations for the Construction of π-Conjugated Frameworks.

Cumulenes have attracted considerable attention due to their unique structural and electronic properties. Despite their high potential for constructing condensed π-conjugated molecules, the synthetic utility of longer cumulenes remains to be established owing to their inherently high reactivity. Conjugated bisbutatrienes having two cumulene moieties linked by a spacer as a mimic of a longer cumulene were evaluated.

Synthesis of Cage-Shaped Borates Bearing Pyrenylmethyl Groups: Efficient Lewis Acid Catalyst for Photoactivated Glycosylations Driven by Intramolecular Excimer Formation.

We describe the synthesis and characterization of a photoactivated boron-based Lewis acid catalyst based on a cage-shaped triphenolic ligand with three pyrenylmethyl moieties. The obtained cage-shaped borate functioned as a photoactivated Lewis acid catalyst thanks to the flexible three pyrenylmethyl moieties. The deformation of the cage-shaped scaffold driven by intramolecular excimer formations of the pyrenes is a critical factor in realizing the photoactivation.

Bis-periazulene (Cyclohepta[]fluorene) as a Nonalternant Isomer of Pyrene: Synthesis and Characterization of Its Triaryl Derivatives.

Bis-periazulene (cyclohepta[]fluorene), which is an unknown pyrene isomer, was synthesized as kinetically protected forms. Its triaryl derivatives - exhibited the superimposed electronic structures of peripheral, polarized, and open-shell π-conjugated systems. In contrast to previous theoretical predictions, bis-periazulene derivatives were in the singlet ground state.

Revisiting Glycosylations Using Glycosyl Fluoride by BF·EtO: Activation of Disarmed Glycosyl Fluorides with High Catalytic Turnover.

Catalytic glycosylations with glycosyl fluorides using BF·EtO are presented. Glycosylations with both armed and disarmed donors were efficiently catalyzed by 1 mol% of BF·EtO in a nitrogen-filled glovebox without the use of dehydrating agents. Our finding is in sharp contrast with conventional BF·EtO-mediated glycosylations, where excess Lewis acid and additives are required.

Synthesis and Catalytic Activity of Atrane-type Hard and Soft Lewis Superacids with a Silyl, Germyl, or Stannyl Cationic Center.

The synthesis and isolation of atrane-type molecules 1E (E=Si, Ge, or Sn) having a cationic group 14 elemental center are reported. The cations 1E act as hard and soft Lewis superacids, which readily interact with various hard and soft Lewis basic substrates. The rigid atrane framework stabilizes the localized positive charge on the elemental center and assists the formation of the well-defined highly coordinated states of 1E .

Characterization of Benzo[a]naphtho[2,3-f]pentalene: Interrelation between Open-shell and Antiaromatic Characters Governed by Mode of the Quinoidal Subunit and Molecular Symmetry.

The singlet open-shell character and antiaromaticity are intriguing features in π-conjugated carbocycles. These two exhibit similar chemical and physical properties. However, they rarely coexist in the same molecule.

Selective Activation of Aromatic Aldehydes Promoted by Dispersion Interactions: Steric and Electronic Factors of a π-Pocket within Cage-Shaped Borates for Molecular Recognition.

Selective bond formations are one of the most important reactions in organic synthesis. In the Lewis acid mediated electrophile reactions of carbonyls, the selective formation of a carbonyl-acid complex plays a critical role in determining selectivity, which is based on the difference in the coordinative interaction between the carbonyl and Lewis acid center. Although this strategy has attained progress in selective bond formations, the discrimination between similarly sized aromatic and aliphatic carbonyls that have no functional anchors to strongly interact with the metal center still remains a challenging issue.

Characterization of Highly Coordinated Allylgermanes: Pivotal Players for Enhanced Nucleophilicity and Stereoselectivity.

Allylgermanes with a 4-, 5-, and 6-coordinated germanium center were characterized by X-ray crystallography. Cationic 6-coordinated group 14 allylmetals, which were hitherto assumed to be a transition-state structure of allylations, were successfully isolated. Forming high coordination states significantly enhanced the reactivity of the allylgermanes.

Synthesis of α-Alkenyl α,β-Unsaturated Ketones via Dehydrogermylation of Oxagermacycles with Regeneration of the Germanium(II) Species.

The synthesis of α-alkenyl α,β-unsaturated ketones using germanium(II) salts is reported. Oxagermacycles derived from α,β-unsaturated ketones with germanium(II) salts and aldehydes can be transformed into α-alkenyl α,β-unsaturated ketones. Ammonium salts promoted the elimination of Ge(II) species to afford the two classes of α-alkenyl α,β-unsaturated ketones in good yields.

Synthesis of Cage-Shaped Aluminum Aryloxides: Efficient Lewis Acid Catalyst for Stereoselective Glycosylation Driven by Flexible Shift of Four- to Five-Coordination.

Monomeric cage-shaped aluminum aryl oxides Al were synthesized using tripodal triphenolic ligands. The Lewis acidity and catalytic activity of the obtained Al·py were investigated. The Lewis acidity of Al·py originates from the flexible change in the coordination number of the aluminum center, allowing the catalytic -glycosylation to occur with a high efficiency and an unusual stereoselectivity.

Open-Shell and Antiaromatic Character Induced by the Highly Symmetric Geometry of the Planar Heptalene Structure: Synthesis and Characterization of a Nonalternant Isomer of Bisanthene.

A nonbenzenoid hydrocarbon, difluoreno[1,9,8- alkj:1',9',8'- gfed]heptalene 1, is synthesized. Experimental and theoretical investigations demonstrate that the planar and symmetric heptalene core within 1 effectively induces the antiaromatic and open-shell character. These properties are not shared by bisanthene 2, a benzenoid isomer of 1.

Enhancement of Antiaromatic Character via Additional Benzoannulation into Dibenzo[ a, f]pentalene: Syntheses and Properties of Benzo[ a]naphtho[2,1- f]pentalene and Dinaphtho[2,1- a, f]pentalene.

Understanding the structure-property relationships in antiaromatic molecules is crucial for controlling their electronic properties and designing new organic optoelectronic materials. Dibenzo[ a, f]pentalene, a structural isomer of dibenzopentalene, displays open-shell and antiaromatic character harmonization, which is not shared by the well-known isomer, dibenzo[ a, e]pentalene. The next questions of interest concern the topological effects of the π-extension on the harmonization of the open-shell and antiaromatic character in the dibenzo[ a, f]pentalene π-system.

Stereocontrolled Synthesis of Triols Containing Four Asymmetric Centers: Application of C, O-Chelated Germyl Enolates to a Diastereoselective Aldol Reaction.

The treatment of α,β-unsaturated ketones with divalent germanium salts cleanly generated C, O-chelated germyl enolates. The aldol reactions of the chelated enolates with the aldehydes achieved a high diastereoselectivity in the construction of the five-membered aldol adducts. Furthermore, the subsequent transformation of the Ge-C bond in the aldol adduct enabled the stereocontrolled synthesis of triols bearing four asymmetric centers.

Construction of Polycyclic π-Conjugated Systems Incorporating an Azulene Unit Following the Oxidation of 1,8-Diphenyl-9,10-bis(phenylethynyl)phenanthrene.

Polycyclic aromatic hydrocarbons (PAHs) that incorporate either heptagons or pentagons consist of non-planar molecular structures with unusual optoelectronic properties, and the design of a relatively simple and efficient method to construct these highly fused π-conjugated systems with odd-membered rings is in high demand. This work describes the use of silver(I) cations to promote the efficient synthesis of azulene-embedded PAH 2, which is a structural isomer of tribenzo[fg,ij,rst]pentaphene 3, via tandem oxidative transannulation between the phenyl and arylethynyl moieties. This method involves a carbophilic interaction of the silver(I) cation with the acetylene units, which facilitates an electron transfer in the initial step.

1,8-Diphenyl-9,10-Bis(arylethynyl)phenanthrenes: Synthesis, Distorted Structure, and Optical Properties.

The synthesis and optical properties of 1,8-diphenyl-9,10-bis(arylethynyl)phenanthrenes, which are distorted phenanthrenes, are reported. The presence of the two phenyl groups at the 1,8-positions of phenanthrene significantly distorts the molecular geometries, as was evidenced by X-ray crystallography. The congested substitution pattern in the K region results in a distorted aromatic framework, which leads to a redshift in the emission spectrum.

Benzenoid Quinodimethanes.

Reactivity and physical properties of π-conjugated hydrocarbon systems depend predominantly on the topology of π-electrons array. Quinoidal conjugations serve as giving diradical character to molecules, leading to unique chemical behaviors. The simplest member of quinodimethanes are o-, m-, and p-quinodimethanes, which are very reactive due to diradical character and cannot be isolated under normal experimental conditions.

Synthesis and Characterization of Dibenzo[a,f]pentalene: Harmonization of the Antiaromatic and Singlet Biradical Character.

Mesityl derivatives of the unknown dibenzopentalene isomer dibenzo[a,f]pentalene were synthesized. The molecular geometry and physical properties of dibenzo[a,f]pentalene were investigated. Dibenzo[a,f]pentalene combines a large antiaromatic and appreciable singlet open-shell character, properties not shared by well-known isomer dibenzo[a,e]pentalene.

Tuning Lewis Acidity by a Transannular p -σ* Interaction between Boron and Silicon/Germanium Atoms Supported by a Cage-Shaped Framework.

Cage-shaped borates tethered by heavier Group 14 elements (Si or Ge) were synthesized. These possess an intramolecularly transannular p -σ* interaction between the boron center and the tethered Si/Ge atom, which allows the precise tuning of their Lewis acidity. The Lewis acidity was investigated by the ligand-exchange reaction rate and IR measurements with the help of theoretical calculation.

C -Symmetric Boron Lewis Acid with a Cage-Shape for Chiral Molecular Recognition and Asymmetric Catalysis.

Chiral Lewis acids play an important role in the precise construction of various types of chiral molecules. Here, a cage-shaped borate 2 was designed and synthesized as a chiral Lewis acid that possesses a unique C -symmetric structure composed of three homochiral binaphthyl moieties. The highly symmetrical structure of 2 with homochirality was clearly elucidated by X-ray crystallographic analysis.

Tautomerization and Dimerization of 6,13-Disubstituted Derivatives of Pentacene.

Two new 6,13-disubstituted pentacene derivatives, 1 c and 1 d, with alkyl and triisopropylsilylethynyl substitution have been synthesized and characterized experimentally and computationally. The alkyl substituted 1 c and 1 d represent the first 6-alkyl-substituted pentacene derivative where the fully aromatic species dominates over the corresponding tautomer. Indeed, no tautomerization product is found for either 1 c or 1 d upon heating or in the presence of catalytic amounts of acid.