Novel rearrangement of N-enoyl oxazolidinethiones to N-substituted 1,3-thiazine-2,4-diones promoted by NbCl5

NbCl₅ has been employed as promoter of a novel rearrangement to afford chiral N-substituted 1,3-thiazine-2,4-diones with one or two new stereogenic centers from di- and trisubstituted N-enoyl oxazolidinethiones. The trisubstituted E-isomers provide the anti-diastereomers mainly.     

Synthesis of N-substituted 2,4-thiazolidinediones from oxazolidinethiones

A novel reaction has been found between oxazolidinethione and bromoacetyl bromide to afford N-substituted 2,4-thiazolidinediones through an intramolecular nucleophilic substitution reaction. Interestingly a step of elimination was carried out in trisubstituted oxazolidinethiones forming a double bond.     

Synthesis and aromatic nucleophilic N-N, N-S and N-O exchange reactions of N,N-dimethyl-2-trifluoroacetyl-1-naphthylamine

We succeeded in the synthesis of N,N-dimethyl-2-trifluoroacetyl-1-naphthylamine (10) by the regioselective deacylation of N,N-dimethyl-2,4-bis(trifluoroacetyl)-1-naphthylamine with trifluoroacetic acid and water. The aromatic nucleophilic substitutions of 10 with various amines, thiols and alcohols proceeded cleanly to give the corresponding N-N, N-S and N-O exchanged products in moderate to excellent yields.     

N-Heterocyclic carbene catalyzed intramolecular nucleophilic addition of carbonyl anion equivalents to enol ethers

The intramolecular nucleophilic addition reaction of acyl anion equivalents to enol ethers is described, which was catalyzed by N-heterocyclic carbenes generated in situ from readily available thiazolium salt. In this transformation, benzofuranones were obtained in excellent yield. In combination with our previous work, the precise mechanistic elucidation for the formation of benzofuranones has been further investigated. A labeling experiment implied that the transformation proceeds through a nucleophilic addition mechanism.     

A synthesis of novel N-sulfonylated β-amino acids

Novel N-sulfonyl β-amino acids were efficiently prepared in a seven-step synthesis starting from Boc protected methanesulfonamide and terminal epoxides. A zinc-mediated allylation of cyclic N-sulfonyl imines readily derived from these building blocks served as a key operation of this sequence.     

Oxidation of N-hydroxyazetidines: A novel synthesis of N-acetoxy β-Lactams and four-membered cyclic nitrones

The N-hydroxyazetidines $\text{2}$ and $\text{3}$ are prepared startinfrom 2,3-dihydroazete 1-oxides ($\text{1a}$ and $\text{1b}$0 by reduction with sodium borohydride and by reaction with a nucleophile, respectively. The N-thydroxyazetidines $\text{2}$ and $\text{3}$ can be oxidized with mercury (II) oxide to the corresponding nitrones $\text{1}$; oxidation of the N-hydroxyazetidine $\text{2a}$ (unsubstituted at C-4) with $\text{two}$ equivalent of lead tetraacetate tyields the N-tacetoxy β-lactam $\text{4}$.     

Amidines as potent nucleophilic organocatalysts for the transfer of electrophilic bromine from N-bromosuccinimide to alkenes

(±)-iso-Amarine is a potent organocatalyst at 1 mol % loading for both the bromoacetoxylation of alkenes with added acetic acid and bromolactonisation of unsaturated carboxylic acids with stoichiometric NBS as the electrophilic bromine source. A simple bromoamidine with an N-Br bond has been characterised crystallographically for the first time. Asymmetric induction in the bromination reactions with enantiopure amidines was zero.     

Some studies on nucleophilic trifluoromethylation using the shelf-stable trifluoromethylacetophenone-N,N-dimethyltrimethylsilylamine adduct

The simple thermal addition product of N,N-dimethyltrimethylsilylamine with 2,2,2-trifluoroacetophenone provides a shelf-stable reagent for nucleophilic trifluoromethylation of both the carbonyl and the imine group.     

Enantioselective nucleophilic addition to N-(2-pyridylsulfonyl)imines by use of dynamically induced chirality

Enantioselective nucleophilic addition of Grignard reagents to N-(2-pyridylsulfonyl)imines in the presence of bis(oxazoline) afforded products with good enantioselectivity. Dynamically induced chirality on the sulfur by coordination of a chiral Lewis acid to a pyridyl nitrogen and one of the sulfonyl oxygens fixes the conformation of the complex and induces enantioselectivity. Since the 2-pyridylsulfonyl group can be easily removed after the addition reaction, it acts not only as a protecting group but also as an efficient stereocontroller.     

Transition state flexibility in nucleophilic attack on carbon

Multi-directional transition state theory qualitatively explains steric effects with hindered nucleophiles.     

A novel method for the formation of N-glycosides using hydroxamate

Direct formation of Asn-linked carbohydrate by N-glycosylation has been difficult, because of the lack of nucleophilicity of carboxamide nitrogen. We report here the novel N-glycosylation using Asn hydroxamate as a glycosyl acceptor. Reaction with glycosyl fluoride or glycosyl trichloroacetimidate afforded N-glycoside and subsequent reduction with SmI₂ gave Asn-linked glucose. Carbamate derived hydroxamates proved to have even enhanced reactivity to give N-glycosides in high yields.     

A novel solid-phase synthesis of di- and trisubstituted N-acyl ureas

A novel, mild method for the synthesis of di- and trisubstituted N-acyl ureas on solid support is described. Addition of carboxylic acids to a resin-bound carbimidoyl chloride gave, initially, an O-acyl isourea which subsequently rearranged to the corresponding N-acyl urea. Trisubstituted N-acyl ureas were assembled on a Wang resin from a wide range of Fmoc amino acids, secondary amines and carboxylic acids. Acid mediated cleavage yielded the products in good yields and excellent purities. In addition, the regioselective synthesis of disubstituted N-acyl ureas is demonstrated with four examples.     

The umpolung of substituent effect in nucleophilic aromatic substitution. A new approach to the synthesis of N,N-disubstituted melamines (triazine triskelions) under mild reaction conditions

By the umpolung of substituent effect 1,3,5-triazines substituted with three dialkylamino groups were prepared under mild reaction conditions by treatment of cyanuric chloride with tertiary amines. Quaternary N-triazinylammonium salts were identified as reactive intermediates activating the triazine ring and strongly promoting the persubstitution of all chlorine atoms. The final degradation of intermediate N-triazinylammonium chlorides proceeded at room temperature or in boiling dichloromethane spontaneously within irreversible evolution of appropriate chloroalkane.     

A novel method for the reduction of sulfoxides with the N,N,N’,N’-tetrabromobenzene-1,3-disulfonamide (TBBDA)/PPh3 system

A new method is described for the reduction of sulfoxides to sulfides using N,N,N’,N’-tetrabromobenzene-1,3-disulfonamide [TBBDA] in combination with triphenylphosphine. Good to excellent yields, short reaction times, high efficiency and facile isolation of the desired products are the advantages of this method.     

A conserved asparagine in a ubiquitin-conjugating enzyme positions the substrate for nucleophilic attack

The mechanism used by the ubiquitin-conjugating enzyme, Ubc13, to catalyze ubiquitination is probed with three computational techniques: Born–Oppenheimer molecular dynamics, single point quantum mechanics/molecular mechanics energies, and classical molecular dynamics. These simulations support a long-held hypothesis and show that Ubc13-catalyzed ubiquitination uses a stepwise, nucleophilic attack mechanism. Furthermore, they show that the first step—the formation of a tetrahedral, zwitterionic intermediate—is rate limiting. However, these simulations contradict another popular hypothesis that supposes that the negative charge on the intermediate is stabilized by a highly conserved asparagine (Asn79 in Ubc13). Instead, calculated reaction profiles of the N79A mutant illustrate how charge stabilization actually increases the barrier to product formation. Finally, an alternate role for Asn79 is suggested by simulations of wild-type, N79A, N79D, and H77A Ubc13: it stabilizes the motion of the electrophile prior to the reaction, positioning it for nucleophilic attack. © 2019 Wiley Periodicals, Inc.     

Moderate generation of sulfenylnitrenes from novel N-sulfenylsulfodiimides

N-Sulfenylated sulfodiimides were first prepared by the reaction of S,S-diphenyl-N-tosylsulfodiimide with arenesulfenyl chlorides under the basic conditions. Thermolysis of S,S-diphenyl-N-(2-nitrophenylsulfenyl)- and S,S-diphenyl-N-(2,4-dinitrophenylsulfenyl)sulfodiimides in the presence of olefins proceeded at 50-80 °C to give the corresponding deiminated S,S-diphenyl-N-tosylsulfimide and N-sulfenylaziridines in very good yields. 2,4-Dinitrophenyl-sulfenylnitrene was trapped by trans- and cis-1-phenylpropenes stereospecifically. The thermolysis temperature of the N-sulfenylsulfodiimides was found to be lower than N-sulfenylsulfoximide and higher than N-sulfenyliminosulfonium salt and very effective to trap the sulfenylnitrene to give the N-sulfenylaziridines in very good yields.     

Synthesis and characterization of novel fluorescent N-glycoconjugates

Novel fluorescent N-glycoconjugates containing d-glucose, glycine and coumarin or naphthalenetriazole derivatives were prepared by peptide synthesis type methods. The fluorescence properties (spectra, quantum yields) of the compounds were evaluated.