Ni-catalyzed α-arylation of secondary α-bromo-α-fluoro-β-lactam: cross-coupling of a secondary fluorine-containing electrophile

A highly diastereoselective cross-coupling reaction of an α-bromo-α-fluoro-β-lactam with a wide range of aryl Grignard reagents was catalyzed by Ni/bis(oxazoline) in yields of up to 98%. The product was obtained diastereoselectively as an anti-isomer. This is the first successful α-arylation of an α-fluoro-β-lactam to produce diverse α-aryl-α-fluoro-β-lactams.     

Controlling the photochemical reactions of alkenes by light-path length effects of a microchannel reactor

Photoirradiation of Me₂CO–H₂O solution of pent-4-en-1-ol (1a) with a high-pressure mercury lamp in a test tube gave 8-hydroxyoctan-2-one (3a) in 66 % yield along with oxetane (4a) and the isomer (4a′) in 10 % yield. Irradiation of the running Me₂CO–H₂O solution of 1a in the flow system of a microchannel reactor (MCR) gave mainly 4a. The photoreaction of 1,1-diphenylethene (2a) with triethylamine gave a Markovnikov-type adduct (5a) and an anti-Markovnikov-type adduct (6a). The use of the MCR enhanced the production of 5a. These phenomena were explained by the light-path length effects of the MCR.     

An Unusual Cyclic System: Derivatives of N-Acetyl [2-Deoxy-β-D-Mannopyranosid]Urono-6,2-Lactam

ABSTRACT

Syntheses are described of a new ring system, namely derivatives of N-acetyl [2-deoxy-β-D-mannopyranosid]urono-6,2-lactam. These were formed by participation of a 2-acetamido-2-deoxy group in the oxidation using pyridinium dichromate of a 6-hydroxyl group in a mannopyranosidic system The structures of the new compounds were determined mainly by NMR experiments inter alia by HMBC techniques.     

Synthetic Studies on Sialoglycoconjugates 40: Stereocontrolled Synthesis of Sialyl Lewis X Epitope and Its Ceramide Derivative

Abstract

Stereocontrolled synthesis of sialyl Le^x epitope and its ceramide derivative with regard to the introduction of galactose or β-D-galactosyl ceramide into the terminal N-acetylglucosamine residue of sialyl Le^x determinant is described. Königs-Knorr condensation of 2-(trimethylsilyl)ethyl 2, 4, 6-tri-O-benzyl-β-D-galactopyranoside (4) with 3, 4, 6-tri-O-acetyl-2-deoxy-2-phthalimido-D-glucopyranosyl bromide (5) gave the desired β-glycoside 6, which was converted into 2-(trimethylsilyl)ethyl O-(2-acetamido-4, 6-O-benzylidene-2-deoxy-β-D-glucopyranosyl)-(l→3)-2, 4, 6-tri-O-benzyl-β-D-galactopyranoside (8) via removal of the phthaloyl and O-acetyl groups, followed by N-acetylation and 4, 6-O-benzylidenation. Glycosylation of 8 with methyl 2, 3, 4-tri-O-benzyl-1-thio-β-L-fucopyranoside (9) gave the α-glycoside (10), which was transformed by reductive ring-opening of the benzyliderie acetal into the acceptor (11). Dimethyl(methylthio)sulfonium triflate (DMTST)-promoted coupling of 11 with methyl O-(methyl 5-acetamido-4, 7, 8, 9-tetra-O-acetyl-3, 5-dideoxy-D-glycero-α-D-galacto-2-nonulopyranosylonate)-(2→3)-2, 4, 6-tri-O-benzoyl-l-thio-β-D-galactopyra-noside (12) afforded the desired pentasaccharide (13), which was converted into the α-trichloroacetimidate 16 via reductive removal of the benzyl groups, then O-acetylation, removal of the 2-(trimethyIsilyl)ethyl group and treatment with trichloroacetonitrile. Condensation of 16 with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-l, 3-diol (18) gave the β-glycoside 19, which was transformed into the title compound 21, via reduction of the azido group, coupling with octadecanoic acid, O-deacylation and hydrolysis of the methyl ester group. On the other hand, O-deacylation of 13 and subsequent hydrolysis of the methyl ester group gave the pentasaccharide epitope 17.     

Synthesis,Structure, and Reactivity of Lewis Base Stabilized Plumbacyclopentadienylidenes

Plumbacyclopentadienylidenes, in which the lead atoms have divalent states and are coordinated by THF, pyridine and N‐heterocyclic carbene, were synthesized and characterized. The THF‐ and pyridine‐stabilized compounds can be regarded as rare examples of hypervalent 10‐X‐4 species. The equilibrium between the THF adduct and the free plumbacyclopentadienylidene was evidenced by spectroscopic analysis and theoretical calculations. The THF adduct in benzene converted into a plumbylene dimer, where one of the lead centers is coordinated by THF and the other lead atom is coordinated by a divalent lead atom, the dimer gradually decomposing into spiroplumbole. The THF adduct unexpectedly reacted with trifluoroborane and trichlorogallane to afford fluoroborole and chlorogallole, which are the first examples of non‐annulated fluoroborole and gallole, respectively.     

Diastereo‐ and Regioselective Addition of Thioamide Dianions to Imines and Aziridines: Synthesis of N‐Thioacyl‐1,2‐diamines and N‐Thioacyl‐1,3‐diamines

Addition reactions of thioamide dianions that were derived from N‐arylmethyl thioamides to imines and aziridines were carried out. The reactions of imines gave the addition products of N‐thioacyl‐1,2‐diamines in a highly diastereoselective manner in good‐to‐excellent yields. The diastereomeric purity of these N‐thioacyl‐1,2‐diamines could be enriched by simple recrystallization. The reduction of N‐thioacyl‐1,2‐diamines with LiAlH₄ gave their corresponding 1,2‐diamines in moderate‐to‐good yields with retention of their stereochemistry. The oxidative‐desulfurization/cyclization of an N‐thioacyl‐1,2‐diamine in CuCl₂/O₂ and I₂/pyridine systems gave the cyclized product in moderate yield and the trans isomer was obtained as the sole product. On the other hand, a similar cyclization reaction with antiformin (aq. NaClO) as an oxidant gave the cis isomer as the major product. The reactions of N‐tosylaziridines gave the addition products of N‐thioacyl‐1,3‐diamines with low diastereoselectivity but high regioselectivity and in good‐to‐excellent yields. The use of AlMe₃ as an additive improved the efficiency and regioselectivity of the reaction. The stereochemistry of the obtained products was determined by X‐ray diffraction.     

Bimetallic Co–Pd alloy nanoparticles as magnetically recoverable catalysts for the aerobic oxidation of alcohols in water

Co–Pd bimetallic alloy nanoparticle catalysts were prepared from CoCl₂, Pd(OAc)₂ and several capping agents with Li(C₂H₅)₃BH. The nanoparticle catalysts were applied to the aerobic oxidation of a variety of alcohols in water to give the corresponding carbonyl products. The catalyst was magnetically recovered and reused for further oxidation. The nanoparticle catalysts were characterized with TEM, ICP, and XPS analyses.     

Synthesis and properties of novel crown ether-annelated 4′,5′-diaza-9′-(1,3-dithiole-2-ylidene)-fluorenes and their ruthenium(II) complexes

Two novel redox-active 1,3-dithiole (DT) ring-fused 4,5-diazafluorene ligands with crown ether moieties (L1 and L2) were synthesized and characterized. The crystal structure of L1 was studied. The electrochemical and spectroscopic properties of these new ligands, as well as the corresponding bis(bipyridine)ruthenium(II) complexes [4: Ru L1(bpy)₂ and 5: Ru L2(bpy)₂], were also been investigated.     

Adsorption and photochemical behaviors of the novel cationic xanthene derivative on the clay surface

Novel tetra-cationic xanthene derivative (Flu) was synthesized. Its adsorption and photochemical behaviors on the clay surface were investigated. Fluorescence quantum yield (?_f) and fluorescence lifetime were 0.50 and 2.9 ns for Flu/clay complex. ?_f of Flu was enough high (>0.1) even at high density conditions (0.080 molecules nm⁻²). It is supposed that the strong interaction between clay and Flu by the ‘Size-Matching Effect’ realizes the highly emissive clay complexes at high density adsorption condition by a suppression of a molecular aggregation, which tends to decrease the photochemical activity.     

Copper‐Catalyzed CH Bond Direct Chalcogenation of Aromatic Compounds Leading to Diaryl Sulfides,Selenides, and Diselenides by Using Elemental Sulfur and Selenium as Chalcogen Sources Under Oxidative Conditions

The reactions of aromatic compounds and elemental chalcogens catalyzed by a copper salt with molecular oxygen as an oxidant were carried out. The reaction of 3‐substituted imidazo[1,5‐a]pyridines and elemental sulfur in the presence of CuTC (copper(I) thiophenecarboxylate) gave the corresponding bisimidazopyridyl sulfides in good to quantitative yields. The reaction proceeded even under aerobic oxidation conditions. The use of a polar solvent was crucial for the reaction, and DMSO (dimethyl sulfoxide) in particular stimulated the reaction. The reaction could be applied to common aromatic compounds, such as N‐methyl indole and dialkyl anilines. The reaction of indole proceeded at the nucleophilic C3 position rather than at the acidic C2 position. In addition, the reaction of dialkyl anilines proceeded with an ortho, para orientation. The reactions of imidazopyridines and elemental selenium under similar conditions gave the corresponding bisimidazopyridyl diselenides along with bisimidazopyridyl monoselenides. The resulting diselenides were readily converted to the corresponding monoselenides with unreacted imidazopyridines under the same conditions. The reaction could be applied to the copolymerization of bifunctional bisimidazopyridines and elemental sulfur to give oligomeric copolymers in quantitative yield.