Published papers

The synthesis of a multiboron heterocycle and its application to a direct amidation catalyst are described. The heterocycle comprised of B3NO2is called DATB. The DATB-catalyzed direct amide formation is well suited for the synthesis of a wide range of amides, including previously intractable ones. The catalysis can also be applied to peptide synthesis and N-acylation of sulfoxi- mines. The most active DATB contains four boron atoms in its structure, and the detailed mecha- nistic study revealed their distinctive roles in the catalytic cycle, depending on the given chemical environment. A pyrimidine containing analog was also developed and evaluated as a more readily accessible amidation catalyst than the original one. The Pym-DATB is now available from a commercial vendor. Current trends and future perspective in the boron - catalyzed direct amidation are also discussed.

A cascade alkene sulfonylation that simultaneously forges C-S and C-C bonds is a highly efficient and powerful approach for directly accessing structurally diverse sulfonylated compounds in a single operation. The reaction was enabled by visible-light-mediated regioselective radical addition of sulfonyl chlorides to 2-arylstyrenes using fac[Ir(ppy)3] as a photocatalyst, demonstrating its unique role in a photocascade process to execute atom transfer radical addition (ATRA) followed by photocyclization. A new class of sulfonyl-substituted fluorenes and pyrroloindoles, which are useful in the field of photoelectronic materials and medicinal chemistry, was produced in excellent yields by this photocascade reaction. In contrast, the cyclization was interrupted when using the [Ru(bpy)3Cl2] catalyst having lower reduction potential, leading only to the formation of a C-S bond and the production of acyclic sulfonylated 2-arylstyrenes under identical reaction conditions. The synthetic utility of the present room-temperature photocatalysis is enhanced by the broad availability of bench-stable sulfonyl chlorides and unactivated olefins, thereby providing a cost-effective and broad-scope protocol.

A fluorine-containing tetrasubstituted stereogenic center is a highly valued structural feature in medicinal chemistry. Herein, we describe the direct coupling of racemic α-fluoronitriles and aldehydes promoted by a chiral CuI/Barton's base catalytic system, delivering α-tetrasubstituted α-fluoro-β-hydroxynitriles with satisfactory stereoselection. The stereochemical course was positively biased by the combined use of asymmetrical achiral thiourea as a supplementary ligand for CuI, which significantly enhanced the stereoselectivity. Both aromatic and aliphatic aldehydes were implemented to provide densely and stereoselectively functionalized chiral building blocks with aliphatic and aromatic tails.

A direct catalytic asymmetric addition of acetonitrile to aldehydes that realizes over 90 % ee is the ultimate challenge in alkylnitrile addition chemistry. Herein, we report achieving high enantioselectivity by the strategic use of a sterically demanding NiII pincer carbene complex, which afforded highly enantioenriched β-hydroxynitriles. This highly atom-economical process paves the way for exploiting inexpensive acetonitrile as a promising C2 building block in a practical synthetic toolbox for asymmetric catalysis.

The stereoselective preparation of 1,2,3-substituted cyclopropanes from α,β-unsaturated carbonyl compounds in the carboxylic acid oxidation state through Michael addition-initiated ring-closure reactions is a significant challenge in organic synthesis. Herein, the previously elusive catalytic asymmetric cyclopropanation of α,β-unsaturated amides with stabilized sulfur ylides has been efficiently accomplished utilizing a chiral Cu(I) complex. This Lewis acid catalytic system effectively converts a wide range of electron-deficient alkenes into the corresponding 1,2,3-trisubstituted cyclopropanes under mild reaction conditions in good to excellent yields with both high to excellent enantio- and diastereoselectivities. The resulting enantiomerically enriched cyclopropane amides can be readily diversified into promising synthetic intermediates such as β-aminocyclopropanecarboxylic acids with the facile recovery of the 7-azaindoline auxiliary without influencing the optical purity of the cyclopropane unit, which highlights the synthetic efficacy of this catalytic approach.

C4N4 fluorophores comprise a recently disclosed new class of emissive organic molecules with modular synthetic capabilities. Herein, we report a new synthetic protocol toward asymmetrically di arylated C4N4 fluorescent materials. Direct monoarylation of 1-naphthol is exploited to suppress undesired diarylation and to provide a free phenolic hydroxy group for prospective linking to a molecule of interest. Installation of the second aromatic unit in order to acquire fluorescent properties is achieved by Suzuki-Miyaura cross-coupling.

Oxa-TriQuinoline (o-TQ) is a new entry in the collection of aza-oxa-crown compounds featuring a semi-rigid flexible conformation and a tripodal ligation capability through three quinoline units. Herein, we describe the installation of functional groups and aromatic substituents on the outer edge of o-TQ to modulate its physicochemical properties. Amino and bromo substituents were regioselectively introduced at the 5-position, forming bowl-shaped Cu(I) complexes in which three quinoline units coordinated to Cu(I). X-ray crystallography indicated that these o-TQ derivatives preferred an almost identical geometry in both the absence and presence of Cu(I). In contrast to o-TQ, some new o-TQ derivatives exhibited photoluminescent properties in solution and/or in the solid state depending on the substituents.

An iterative hydride reduction/oxidation process was promoted under ambient conditions by a quasi-planar iminium cation rigidified by two concatenated quinoline units. The iminium proton was fixed by hydrogen bonding from neighboring quinoline nitrogen atoms, rendering the imine highly susceptible to hydride reduction with weak reductants, e.g., 1,4-dihydropyridines. The thus-formed amine was readily oxidized by molecular oxygen to regenerate the quasi-planar iminium cation under ambient conditions. This process was exploited for catalytic oxidation of 1,4-dihydropyridines as well as 9,10-dihydroacridine to highlight an intriguing rigidity- driven catalysis.

The C4N4 fluorophore is an intense fluorescence emitter featuring a 2,5-diaminopyrimidine core comprising four carbon and four nitrogen atoms. A series of C4N4 derivatives was photochemically dimerized at the 5-amino group, furnishing overcrowded ortho-tetraaryl-substituted diaryl azo compounds with a characteristic skewed structure revealed by X-ray crystallography. The photoquenched azo-C4N4s are useful for fluorescently visualizing cells under hypoxic conditions.

Diboron substructures have emerged as a promising scaffold for the catalytic dehydrative amidation of carboxylic acids and amines. This Letter describes the design, synthesis, and evaluation of the first isolable N(BOH)2 compound as an amidation catalyst. The new catalyst outperforms the previously reported B3NO2 heterocycle catalyst, with respect to turnover frequency, albeit the former gradually decomposes upon exposure to amines. This work opens up an avenue for designing a better catalyst for direct amidation.

Nitrogen-containing macrocycles have attracted sustained attention because of their fascinating structures and extensive applications in organic chemistry, therapeutic developments, and materials science. The nitrogen atoms in the macrocycles play important roles in the interaction with metal cations or small molecules, endowing their potential in catalysis, fluorescent sensors, and host–guest chemistry. In this context, herein we summarize highly symmetric nitrogen-containing N3/N4/N6 macrocycles comprising pyrroles, pyridines, quinolines, and (iso)indoles as key N-heteroarenes. The direct and indirect connectivity of N-heteroarene subunits allows for the construction of both flat and non-flat cyclic architectures. The synthesis, structure, and properties of these macrocycles are highlighted.

An efficient method for the synthesis of versatile intermediates for biologically interesting 13-deoxy- and 9,13-dideoxyphorbol ester analogs is described. First,more efficient synthetic routes to the bicyclic ketones 7 and 8, which are well-known intermediates for the synthesis of 13-deoxyphorbols, than the previous one were established. Second, 7 and 8 were successfully converted to the intermediates 19, 25 and 27 for the synthesis of 9,13-dideoxyphorbols using Peterson reaction, oxymercuration and nitrile oxide cycloaddition as key steps. (C) 2000 Elsevier Science Ltd. All rights reserved.

Two case studies regarding the development of rare earth metal-based asymmetric catalysts are summarized, with particular focus on the process of refining catalysts amenable to industrial applications. Amide-based chiral ligands in combination with lanthanum or neodymium cations furnished robust catalytic systems for asymmetric amination or nitroaldol reactions, respectively. Although rare earth metal catalysis is generally characterized by a peculiar coordination chemistry and Lewis acidic catalytic functions, its wide availability and moderate tolerance to moisture are also important features to be noted, making the application of rare earth metal catalysis beneficial for industrial large-scale synthesis.

For decades, the planarity of the amide functional group has garnered sustained interest in organic chemistry, enticing chemists to deform its usually characteristic high-fidelity plane. As opposed to the construction of amides that are distorted by imposing rigid covalent bond assemblies, we demonstrate herein the deformation of the amide plane through increased steric bulk in the periphery of the amide moiety, which is induced by coordination to metal cations. A crystallographic analysis revealed that the thus obtained amides exhibit significant pyramidalization and twisting upon coordination to the metals, while the amide functional group remained intact. The observed deformation, which should be attributed to through-space interactions, substantially enhanced the solvolytic cleavage of the amide, providing compelling evidence that temporary crowding in the periphery of the amide functional group may be used to control the reactivity of amides.

The first protocol for the asymmetric synthesis of 2,3,3,3-tetrafluoro-2-methyl-1-arylpropan-1-amines which function as fluorinated surrogates for alpha-isopropylbenzylamines in SAR-studies is presented herein. Crucial for the successful synthesis was the application of a recently developed direct catalytic asymmetric Mannich-type reaction of fluorinated amide for the key bond-forming step. The utility of this versatile protocol was demonstrated by the synthesis of fluorinated analogues of a T-type selective Ca2+ channel blocker and a prolylcarboxypeptidase inhibitor. The predominant conformation of their fluorinated analogues was investigated by X-ray crystallography and NMR spectroscopy which revealed a strong influence of a fluorine mediated gauche effect. (C) 2016 Elsevier B.V. All rights reserved.

A catalytic asymmetric aldol reaction directly employing amides as latent enolates has remained elusive because of the resistance of amides to enolization. A direct aldol reaction of alpha-alkylarnides without any electron-withdrawing group harnessed by specific activation of 7-azaindoline amides under soft Lewis acid/Bronsted base cooperative catalysis is reported. Diastereo- and enantioselective coupling with ynals and aromatic aldehydes as well as divergent functional group interconversion of the amide provided expeditious access to a variety of aliphatic and aromatic chiral building blocks.

A linear molecular architecture equipped with complementary three-fold hydrogen-bonding units embedded with a photoswitchable trans-tetrafluoroazobenzene moiety was synthesized. The transto cis photoisomerism of the azobenzene unit induced drastic changes in the molecular architecture as a result of intramolecular hydrogen bonding as evidenced by NMR spectroscopy and size exclusion chromatography. A minute stereogenic element in the linear trans state enabled stereoselective folding into the cis state, thus producing a globular architecture with enhanced chiroptical property.

An anti-selective catalytic asymmetric nitroaldol reaction was implemented in a continuous-flow reaction platform for the synthesis of a key intermediate of a drug candidate. The requisite solid-phase catalyst was readily prepared by mixing an amide-based chiral ligand and inexpensive inorganic salts, NdCl3 center dot 6H(2)O and (NaOBu)-Bu-t, without covalent bond linkages. The flow system was operated with 2-Me-THE as the eluent for ca. 400 h to provide a crude nitroaldol adduct in a highly stereoselective manner with no work-up procedure, reaching turnover number over 1600. Facile reduction of the nitro group of the product afforded a key intermediate of AZD7594, a therapeutic candidate for asthma and chronic obstructive pulmonary disease. (C) 2017 Elsevier Ltd. All rights reserved.