Crystallization of racemic 4-arylsulfonyl-2(5H)-furanones: reproducibility of homochiral associates,conditions for the spontaneous resolution of enantiomers and the formation of racemic compounds,the role of intermolecular interactions

Crystallization of three 4-arylsulfonyl-2(5H)-furanones from chloroform leads to the formation of a conglomerate of sulfone with para-tolyl substituent and racemic crystals of chloro and bromo analogs. The high degree of similarity of the crystal packings of a homochiral crystal and racemic compounds, viz., the similar type of the homochiral hydrogen-bonded chains and analogous three-dimensional homochiral layers additionally stabilized by the interactions of the type C=O…C=O and C-H…O, allowed us to suggest the presence of the second, “missing” form for each sulfone. A directed search for the “missing” forms revealed the existence of the racemic modification of sulfone with the para-tolyl fragment formed during a very slow crystallization of the compound from benzene. No conglomerates of bromo and chloro analogs were found. Topological analysis of the electron density distribution performed by quantum chemical calculations using density functional theory (PBE1PBE, 6–31G(d,p)) showed the higher energy favorability of intermolecular interactions in the homochiral chains as compared to the hypothetical heterochiral associates.     

Oxidative Addition to Palladium(0) Diphosphine Complexes: Observations of Mechanistic Complexity with Iodobenzene as Reactant

Using a combination of electrochemical and NMR techniques, the oxidative addition of PhX to three closely related bis‐diphosphine P₂Pd⁰ complexes, where the steric bulk of just one substituent was varied, has been analysed quantitatively. For the complex derived from MetBu₂P, a rapid reaction ensued with PhI following an associative mechanism, and data was also obtained by cyclic voltammetry for PhOTs, PhBr and PhCl, revealing distinct relative reactivities from the related (PCx₃)₂Pd complex (Cx=cyclohexyl) previously studied. The corresponding EttBu₂P complex reacted more slowly with PhI and was studied by NMR spectroscopy. The reaction course indicated a mixture of pathways, with contribution from a component that was [PhI] independent. For the CxtBu₂P complex, reaction was again monitored by NMR spectroscopy, and was even slower. At high PhI concentrations reaction was predominantly linear in [PhI], but at lower concentrations the [PhI] independent pathway was again observed, and an accelerating influence of the reaction product was observed over the concentration range. The NMR spectra of the EttBu₂P and CxtBu₂P complexes conducted in C₆D₆ shows some line broadening that was augmented on addition of PhI. NMR experiments carried out in parallel show that there is rapid ligand exchange between free phosphine and the Pd₂Pd complex and also a slow ligand crossover between different P₂Pd complexes. DFT calculations were carried out to further test the feasibility of C₆D₆ involvement in the oxidative addition process, and located Van der Waals complexes for association of the P₂Pd⁰ complexes with either PhI or benzene. PhI or solvent‐assisted pathways for ligand loss are both lower in energy than direct ligand dissociation. Taken all together, these results provide a consistent explanation for the surprising complexity of an apparently simple reaction step. The clear dividing line between reactions that give a di‐ or monophosphine palladium complex after oxidative addition clarifies the participation of the ligand in coupling catalysis.     

Cocrystallization of diastereomers in the series of 2(5<Emphasis Type="Italic">H</Emphasis>)-furanone bis-thioethers based on 1,2-phenylenedimethanethiol

Crystallization of diastereomeric mixtures of 2(5H)-furanone bis-thioethers, in the molecules of which two unsaturated γ-lactone rings are bound by 1,2-phenylenedimethanethiol bridge through their carbon atoms C(4), was studied. A rare case of cocrystallization of meso- and d,l-diastereomers for bis-thioethers with the small-size methoxy or hydroxy substituents at the asymmetric carbon atom was observed.     

One‐Pot Evolution of Ageladine A through a Bio‐Inspired Cascade towards Selective Modulators of Neuronal Differentiation

A bio‐inspired cascade reaction has been developed for the construction of the marine natural product ageladine A and a de novo array of its N1‐substituted derivatives. This cascade features a 2‐aminoimidazole formation that is modeled after an arginine post‐translational modification and an aza‐electrocyclization. It can be effectively carried out in a one‐pot procedure from simple anilines or guanidines, leading to structural analogues of ageladine A that had been otherwise synthetically inaccessible. We found that some compounds out of this structurally novel library show a significant activity in modulating the neural differentiation. Namely, these compounds selectively activate or inhibit the differentiation of neural stem cells to neurons, while being negligible in the differentiation to astrocytes. This study represents a successful case in which the native biofunction of a natural product could be altered by structural modifications.     

REPRODUCIBILITY OF A HOMOCHIRAL HYDROGEN-BONDED CHAIN IN CONGLOMERATE AND RACEMIC COMPOUND CRYSTALS OF THE TRIAZOLE DERIVATIVE OF 3-PYRROLINE-2-ONE

Journal of Structural Chemistry - The crystal structures of 3-chloro-5-hydroxy-1-(4-methylbenzyl)-4-[4-phenyl-1H-1,2,3-triazole-1-yl]-1,5-dihydro-2Н-pyrrol-2-one rac-1 and...     

Highly reactive “RIKEN click” probe for glycoconjugation on lysines

One pot double click strategy containing strain-promoted click-reaction followed by 6π-azaelectrocyclization (RIKEN click reaction) has worked well in the synthesis of multivalent homogeneous and heterogeneous N-glycoalbumins. We have slightly changed the structure of linker unsaturated aldehyde used in this method. As a result it can be easily synthesized from commercially available material and furthermore, the enhancement of its reactivity towards both click-reactions was observed. The data described in this Communications facilitate the usage of the double click strategy as a general method for the synthesis of a variety of neo-N-glycoproteins.     

Reactions of 2-sulfanylethanol with mucochloric acid and its derivatives

Mucochloric acid reacted with 2-sulfanylethanol in the presence of triethylamine to give 3-chloro-5-hydroxy-4-(2-hydroxyethylsulfanyl)furan-2(5H)-one which underwent acid-catalyzed cyclization to 7-chloro-2,3,4a,6-tetrahydrofuro[2,3-b][1,4]oxathiin-6-one. Likewise, reactions of 5-alkoxy-3,4-dichlorofuran-2(5H)-ones with 2-sulfanylethanol in the presence of triethylamine involved replacement of chlorine in position 4 of the furan ring with formation of the corresponding 4-(2-hydroxyethylsulfanyl) derivatives. The reaction of mucochloric acid with 2-sulfanylethanol in excess aqueous potassium hydroxide resulted in the formation of an acyclic product, 3-(2-hydroxyethylsulfanyl)-2-chloroprop-2-enoic acid. The structure of 7-chloro-2,3,4a,6-tetrahydrofuro[2,3-b][1,4]oxathiin-6-one and 3-(2-hydroxyethylsulfanyl)-2-chloroprop-2-enoic acid was proved by X-ray analysis.     

Aryl bromide/triflate selectivities reveal mechanistic divergence in palladium-catalysed couplings; the Suzuki-Miyaura anomaly

In palladium-catalysed cross-coupling reactions, the outcome of competition between aryl bromides and aryl triflates depends on the nucleophilic partner; Suzuki couplings with R-B generally follow a different pattern from other R-M species.     

Mechanism of electrochemical reduction of 5-thio derivatives of 2(5H)-furanone

The anionoid elimination of the substituent from position 5 of the lactone ring is the predominant pathway of electrochemical reduction of 5-arylsulfanyl- and 5-arylsulfonyl-3,4-dichloro-2(5H)-furanones in acetonitrile. The contribution of the competing elimination of the chloride ion increases on going to 3,4-dichloro-5-ethylsulfanyl-2(5H)-furanone. An experimental criterion based on the morphology of cyclic voltammograms was proposed for identification of a particular pathway of electroreduction of 2(5H)-furanone derivatives.

     

Reactions of 2-mercaptoacetic acid with mucochloric acid and its derivatives

The stable products of reactions of mucochloric acid and some of its ethers with 2-mer-captoacetic acid were synthesized and characterized. The variation of experimental conditions allowed targeted introduction of a sulfur- containing fragment into particular position of the heterocycle: the reaction in aqueous potassium hydroxide gives 3-substituted 2(5H)-furanone the triethylamine additive in nonaqueous solvents facilitates the formation of 4-substituted products, and acid catalysis results in the replacement of the hydroxy (methoxy) group at C(5). (3,4-Dichloro-2-oxo-2,5-dihydrofuran-5-ylthio)ethanoic acid and (3-chloro-5-hydroxy-2oxo-2,5dihydrofuran-4-ylthio)ethanoic acid were characterized by X-ray diffraction; their crystal and gas-phase structures were discussed. The 5-monosubstituted product crystallizes as a racemate, while 4monosubstituted product, as a conglomerate.