Synthesis and application of novel carbohydrate-based ammonium and triazolium salts

The synthesis of nine new carbohydrate-based quaternary ammonium salts and two new triazolium salts starting from d-glucose has been accomplished. Our synthesis utilized the regio- and stereoselective ring opening reaction of 2,3-anhydro sugars by nucleophilic reagents to afford the key intermediates. In these new types of phase transfer catalysts, the ammonium and triazolium functions are directly attached to the carbohydrate scaffold in different positions (2-, 3-, 6-positions of the sugar). The efficiency of the altrose- and glucose-based quaternary salts were tested in the alkylation of N-(diphenyl) methylene glycine tert-butyl ester with benzyl bromide. To our knowledge this is the first example when sugar-based quaternary ammonium or triazolium salts were used successfully as phase transfer catalysts. The enantiomeric recognition ability of the synthesized salts towards racemic Mosher’s acid silver salt was also investigated by ¹⁹F NMR spectroscopy.     

Metal-free synthesis of pyridin-2-yl ureas from 2-aminopyridinium salts

An unprecedented base promoted domino approach has been developed for the synthesis of pyridin-2-yl urea derivatives via the reaction of 2-aminopyridinium salts and arylamines. The developed strategy tolerated a wide range of functional groups and afforded pyridin-2-yl ureas in moderate to good yields. The reaction was postulated to involve tandem cyclization, intermolecular nucleophilic addition, ring opening, and demethylation.     

Synthesis and properties of novel dialkylaminocarbenium salts

Novel dialkylaminocarbenium salts with metallocomplex counter ions were prepared by the reaction of phosgene with either DMF or tetramethylurea in the presence of metal chlorides. Reactions of organosilicon amides with phosgene gave corresponding carbenium salts, while organosilicon ureas yielded aminoiminocarbenium salts. Dialkylaminochlorocarbenium salts were reduced with hydrosilanes to give dialkylaminocarbenium, salts and can be easily hydrolyzed to afford either amides or ureas. Pathways of the reaction with water and alcohols depend on the nature of reagent and the reaction conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1035–1040, May 1997.     

Single Atom Ring Contraction of Peptide Macrocycles Using Cornforth Rearrangement

Site-selective transformations of densely functionalized scaffolds have been a topic of intense interest in chemical synthesis. Herein we have repurposed the rarely used Cornforth rearrangement as a tool to effect a single-atom ring contraction in cyclic peptide backbones. Investigations into the kinetics of the rearrangement were carried out to understand the impact of electronic factors, ring size, and linker type on the reaction efficiency. Conformational analysis was undertaken and showed how subtle differences in the peptide backbone result in substrate-dependent reaction profiles. This methodology can now be used to perform conformation-activity studies. The chemistry also offers an opportunity to install building blocks that are not compatible with traditional C-to-N iterative synthesis of macrocycle precursors.     

Tandem and chemoselective synthesis of benzil derivatives from styrene and arene diazonium salts

A facile and practically applied protocol for synthesis of benzil derivatives using styrene and arene diazonium salts is reported. Pd(OAc)₂/SeO₂ catalytic system was found to be efficient for chemoselective synthesis of benzil. Selenium dioxide works well as an oxidant under milder reaction conditions. Moderate to very good yields of the desired products were obtained.     

Rapid thermal analysis of processes of thermal decomposition of mineral salts

Kinetic curves of thermal decomposition and synthesis of mineral salts are obtained in the conditions of rapid heating approaching the heating conditions in a low-temperature plasma flow. The kinetic characteristics are used in calculations of transformations in the path of a chemical plasma reactor.

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Zusammenfassung Für thermische Zersetzung und Synthese von Mineralsalzen wurden die kinetischen Kurven unter den Bedingungen schnellen Aufheizens in Annäherung der Aufheizbedingungen in einem Niedertemperatur-Plasmastrom ermittelt. Die kinetischen Eigenschaften wurden zur Berechnung der Umwandlungen bei einem chemischen Plasmareaktor verwendet.

     

Synthesis of 8‐Desmethoxy Psymberin: A Putative Biosynthetic Intermediate Towards the Marine Polyketide Psymberin

The synthesis of a putative biosynthetic precursor of psymberin including a formal synthesis of the natural product is described. The key step towards the densely functionalized tetrahydropyran core was an enantioselective catalytic Mukaiyama aldol reaction using a titanium(IV)–BINOL catalyst system. syn‐Selective reduction followed by ozonolysis led to a rapid assembly of the tetrahydropyran ring. This flexible approach also allows the synthesis of similar fragments of other complex molecules such as bryostatins and pederins. The syn‐selective coupling between the tetrahydropyran and the aromatic aldehyde was achieved using a boron‐mediated aldol reaction which was followed by further transformations to complete the synthesis of the precursor as well as the formal synthesis of the natural product.     

Structure Elucidation and Total Synthesis of Kulkenon

The impressive biological profile of secondary metabolites isolated from strains of Sorangium cellulosum prompted us to initiate synthetic studies on kulkenon, also isolated from Sorangium cellulosum. The synthesis features a syn‐selective vinylogous Kobayashi aldol reaction, recently developed by us, and a ring‐closing intramolecular Heck reaction as the pivotal transformations. Comparison of the NMR spectra of the authentic and synthetic material revealed that the proposed configuration had to be revised. A combination of molecular modeling and NOE experiments was used to propose the revised configuration, which was confirmed by a new synthesis.     

Dinitramide and its salts

A strategy of organic synthesis has been developed for a new class of inorganic compounds,viz., dinitramide and its metal, ammonium, and substituted ammonium salts. The basic concepts have been tested in model reactions of -substituted derivatives ofN-alkyl-N-nitrotoluenesulfonamides with bases and have been confirmed by the decyanoethylation ofN,N-dmitro--aminopropionitrile taken as an example.In the communications of this series, we are going to report the results of work on dinitramide carried out in 1970–1980 that could not be published previously. The synthesis of dinitramide salts was first published in the patent literature in 1992. 1,2Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 94–97, January, 1994.     

Electronic absorption spectra of pyrylium and benzodihydrochromenylium salts

The electronic absorption spectra of benzodihydrochromenylium, tetrahydrochromenylium, and dichloropyrylium salts were studied for the first time. It was noticed that intramolecular charge transfer takes place mainly between the substituent at position 4 of the pyrylium ring and the π-system of the cation as a whole, while the bathochromic shift depends substantially on the geometry of the molecule. It was shown that the chlorine atoms have an effect on the form of the spectra when they are introduced into the ring of the pyrylium cation and into the aryl substituents. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1152–1159, August, 2008.     

Asymmetric Total Synthesis of (−)‐Stenine and 9a‐epi‐Stenine

A route for the asymmetric synthesis of (?)‐stenine, a member of the Stemona alkaloid family used as folk medicine in Asian countries, is described. The key features of the sequence employed include stereoselective transformations on a cyclohexane ring controlled by a chiral auxiliary unit and an intramolecular Mitsunobu reaction to construct the perhydroindole ring system. By using an intermediate in the route to (?)‐stenine, an asymmetric synthesis of 9a‐epi‐stenine was also executed. The C(9a) stereocenter in 9a‐epi‐stenine was installed by using a Staudinger/aza‐Wittig reaction of a keto–azide precursor followed by reduction of the resulting imine. The results of this effort demonstrate the applicability of the chiral auxiliary based strategy to the preparation of naturally occurring alkaloids that contain highly functionalized cyclohexane cores.     

Reactions of isoquinoline derivatives with pyridinium salts yielding 4-naphthylpyridines

Regiospecific introduction of the 2-naphthyl residue into position 4 of the pyridine ring occurs in the reactions of isoquinolinium salts with 4-methylpyridinium salts through the intermolecular transformation of the isoquinoline bicyclic system involving the methyl group of the pyridinium salt. The reaction occurs under the action of methylammonium sulfite in an aqueous medium on heating. This method provides ring transformation not only for isoquinolinium salts but even for unsubstituted isoquinoline.     

Effect of the reaction state on the polymerization of p-xylenesulfonium salts

1,4-Phenylenebis(methylene) sulfonium salts were polymerized under different conditions to yield p-xylylene sulfonium salt polyelectrolytes in a broad range of molecular weights. The aqueous reaction mixture formed a reversible gel at initial monomer concentrations higher than 1.0M, but at lower concentrations it remained as an emulsion until reaction completion. The effect of reaction time on intrinsic viscosities and polymer yields for both the emulsion and the gel state is discussed. The higher yields obtained when the reaction was carried out in the presence of a water-immiscible organic solvent were apparently due to the effect of this solvent on increasing the concentration of the reactive intermediate that led to the polyelectrolyte. Both the addition of an organic solvent and the variation of the initial monomer concentrations allowed some control over the molecular weight of the polyelectrolyte formed.     

Studies on cyclization of o-(alka-1,3-diynyl)arenediazonium salts

The Richter reaction of o-(alka-1,3-diynyl)arenediazonium salts, obtained by diazotization of diacetylenic derivatives of anilines, leads to 3-alkynyl-4-chloro- or 3-alkynyl-4-bromocinnolines and/or 3-alkynyl-4-hydroxycinnolines (the latter cyclize into furo[3,2-c]-cinnolines under the reaction conditions). 3-Alkynyl-4-chlorocinnolines undergo solvolysis in methanol giving rise to 3-alkynyl-4-methoxycinnolines, the subsequent hydrolysis of which also gives furo[3,2-c]cinnolines. Effects of the nature of substituents in the aromatic ring and of the reaction conditions on the product composition and yields have been established. The reaction course has been studied by spectrophotometry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1693–1700, August, 2008.     

Synthesis,thermal and lyotropic liquid crystalline properties of protic ionic salts

A series of protic ionic salts were synthesised by a simple acid–base reaction from various pyridine derivatives and dodecylbenzenesulfonic acid in a common organic solvent and characterised in terms of their thermal and lyotropic liquid crystalline properties using various experimental techniques. All of them exhibited lyotropic liquid crystalline phases in toluene, methanol, acetonitrile, dimethyl sulfoxide and water. Their critical concentrations for the formation of biphasic solutions and concentrations for the formation of lyotropic solutions were quite broad depending on the dielectric constants of the solvents. Their lyotropic phases were identified as lamellar phases, since their textures exhibited bâtonnets, oily streaks and mosaic textures. They can potentially be used for many organic transformations, which may have implications in green chemistry.     

Catalyst-free Friedel-Crafts reaction of 1-(N-acylamino)alkyltriarylphosphonium salts with electron-rich arenes

Friedel-Crafts reaction of 1-(N-acylamino)alkyltriarylphosphonium salts with arenes or heteroarenes without the need for any catalyst provided access to a wide range of biologically interesting N-(1-arylalkyl)amides or 1-arylalkylphosphonium salts which can be of great interest in the chemistry of ylides and phosphonium ionic liquids. Depending on reaction conditions and substrate structure, the reaction can be conducted selectively with high yields toward each of the above-mentioned products. Mechanistic aspects of the above transformations were also considered.     

Flexible,dicationic imidazolium salts for in situ application in palladium‐catalysed Mizoroki–Heck coupling of acrylates under aerobic conditions

The synthesis, characterization and in situ catalytic performance of new unsymmetric N,N′‐disubstituted imidazolium‐based dicationic salts in Mizoroki–Heck coupling of acrylates with aryl bromides under aerobic conditions are described. A series of flexible dicationic salts with varying steric and electronic properties were synthesized in good to excellent yields. All the salts were well characterized using spectroscopic techniques. X‐ray diffraction analysis of two salts with the same dicationic backbone and different counter anions shows that the ligand adopts two different conformations which are influenced by the nature of the anion. Thus, the ligand is capable of changing its conformation according to the change in environment due to its flexible nature. All the synthesized imidazolium salts were found to be active in in situ palladium‐catalysed Mizoroki–Heck coupling under aerobic conditions. Amongst the salts, the hydroxyl‐functionalized imidazolium salt, incorporating the features of both bidentate chelating O,O ligand and carbene, shows the maximum catalytic activity. A variety of aryl and heteroaryl methyl and ethyl cinnamates were synthesized using these imidazolium salts as preligands. In addition, NMR studies confirm in situ generation of normal N‐heterocyclic carbenes from the C‐2 position of imidazol‐2‐ylidene ring. The mercury poisoning test was also performed to ascertain the nature of catalytically active palladium species. Aerobic conditions, low catalytic loading (0.5 mol%), shorter reaction times, broad functional group tolerance and good to excellent isolated yields are some of the significant features of the novel catalytic systems described here. Copyright © 2016 John Wiley & Sons, Ltd.     

Enantioselective Total Synthesis of (+)‐Plumisclerin A

The first and enantioselective total synthesis of (+)‐plumisclerin A, a novel unique complex cytotoxic marine diterpenoid, has been accomplished. Around the central cyclopentane anchorage, a sequential ring‐formation protocol was adopted to generate the characteristic tricycle[4.3.1.0^1,5]decane and trans‐fused dihyrdopyran moiety. Scalable enantioselective La^III‐catalyzed Michael reaction, palladium(0)‐catalyzed carbonylation and SmI₂‐mediated radical conjugate addition were successfully applied in the synthesis, affording multiple grams of the complex and rigid B/C/D‐ring system having six continuous stereogenic centers and two all‐carbon quaternary centers. The trans‐fused dihyrdopyran moiety with an exo side‐chain was furnished in final stage through sequential redox transformations from a lactone precursor, which overcome the largish steric strain of the dense multiring system. The reported total synthesis also confirms the absolute chemistries of natural (+)‐plumisclerin A.     

Directed Remote Lateral Metalation: Highly Substituted 2‐Naphthols and BINOLs by In Situ Generation of a Directing Group

A general synthesis of highly substituted 2‐naphthols based on a new carbanionic reaction sequence is demonstrated. The reaction exploits the dual nature of lithium bases consisting of consecutive ring opening of readily available coumarins with either LiNEt₂ or LiNiPr₂ into Z‐cinnamamides, thus generating a directing group in situ and allowing, by conformational freedom, a lateral directed remote metalation for ring closure to give the aryl 2‐naphthols in good to excellent yields. These transformations can be combined to provide a more efficient one‐pot process. Mechanistic insight into the remote lateral metalation step, demonstrating the requirement of Z‐cinnamamide, is described. Application of this methodology to the synthesis of highly substituted 3,3′‐diaryl BINOL ligands is also reported.     

9‐Membered Carbocycle Formation: Development of Distinct Friedel–Crafts Cyclizations and Application to a Scalable Total Synthesis of (±)‐Caraphenol A

Explorations into a series of different approaches for 9‐membered carbocycle formation have afforded the first reported example of a 9‐exo‐dig ring closure via a Au^III‐promoted reaction between an alkyne and an aryl ring as well as several additional, unique Friedel–Crafts‐type cyclizations. Analyses of the factors leading to the success of these transformations are provided, with the application of one of the developed 9‐membered ring closures affording an efficient and scalable synthesis of the bioactive resveratrol trimer caraphenol A. That synthesis proceeded with an average yield of 89 % per step (7.8 % overall yield) and has provided access to more than 600 mg of the target molecule.