Enantioselective synthesis of (−)-idiospermuline

The enantioselective total synthesis of the nonacyclic polypyrrolidinoindoline (−)-idiospermuline is described. Stereocontrolled formation of the vicinal quaternary carbon centers is achieved in a single step by dialkylation of an unsymmetrical prostereogenic dienolate with a tartrate-derived chiral dielectrophile. A catalyst-controlled diastereoselective Heck cyclization is employed to form the diaryl-substituted quaternary center.     

The analysis of aliquat-336 by gas chromatography

The determination of the quaternary ammonium components of Aliquat-336 by gas chromatography using tetraheptylammonium chloride as an internal standard is described. The method relies on the fact that long-chain quaternary ammonium salts undergo thermal decomposition at high injection port temperatures to form tertiary amines. The major component in Aliquat-336 is methyldioctyldecylammonium chloride with up to four other quaternary ammonium compounds being present. Aliquat-336 also contains 1-octanol and 1-decanol and some water.     

Ternary inclusion complexes of γ-cyclodextrin with sodium 1-pyrenesulfonate and cationic and anionic organic compounds having an alkyl chain in aqueous solution

The interactions of an organic anion, 1-pyrenesulfonate (PS), with γ-cyclodextrin (γ-CD) and organic cations such as quaternary ammonium compounds (or organic anions such as 1-decanesulfonate) have been examined by means of absorption and fluorescence spectroscopy. At a low concentration of PS, γ-CD forms a 1:1 inclusion complex with PS. PS forms organic cation–organic anion complexes with quaternary ammonium compounds. The organic cation–organic anion complexes of PS form ternary inclusion complexes with γ-CD. Equilibrium constants for the formation of these complexes have been evaluated from the fluorescence intensity change. As an alkyl chain in the quaternary ammonium compound is lengthened, the equilibrium constant for the formation of the ternary inclusion complex is increased. Although PS does not form complexes with organic anions such as 1-decanesulfonate, the organic anions are bound to the γ-CD cavity accommodating a PS molecule to form ternary inclusion complexes. However, the equilibrium constants for the organic anions (1-decanesulfonate etc.) are significantly less than those for the quaternary ammonium compounds. The small equilibrium constants for the organic anions can be ascribed to the electrostatic repulsion between PS and the organic anions.     

Palladium‐Catalyzed Decarbonylative Dehydration for the Synthesis of α‐Vinyl Carbonyl Compounds and Total Synthesis of (−)‐Aspewentins A,B, and C

The direct α‐vinylation of carbonyl compounds to form a quaternary stereocenter is a challenging transformation. It was discovered that δ‐oxocarboxylic acids can serve as masked vinyl compounds and be unveiled by palladium‐catalyzed decarbonylative dehydration. The carboxylic acids are readily available through enantioselective acrylate addition or asymmetric allylic alkylation. A variety of α‐vinyl quaternary carbonyl compounds are obtained in good yields, and an application in the first enantioselective total synthesis of (?)‐aspewentins A, B, and C is demonstrated.     

Palladium‐Catalyzed Decarbonylative Dehydration for the Synthesis of α‐Vinyl Carbonyl Compounds and Total Synthesis of (−)‐Aspewentins A,B, and C

The direct α‐vinylation of carbonyl compounds to form a quaternary stereocenter is a challenging transformation. It was discovered that δ‐oxocarboxylic acids can serve as masked vinyl compounds and be unveiled by palladium‐catalyzed decarbonylative dehydration. The carboxylic acids are readily available through enantioselective acrylate addition or asymmetric allylic alkylation. A variety of α‐vinyl quaternary carbonyl compounds are obtained in good yields, and an application in the first enantioselective total synthesis of (−)‐aspewentins A, B, and C is demonstrated.     

Iridium‐Catalyzed Stereoselective Allylic Alkylation Reactions with Crotyl Chloride

The development of the first enantio‐, diastereo‐, and regioselective iridium‐catalyzed allylic alkylation reaction of prochiral enolates to form an all‐carbon quaternary stereogenic center with an aliphatic‐substituted allylic electrophile is disclosed. The reaction proceeds with good to excellent selectivity with a range of substituted tetralone‐derived nucleophiles furnishing products bearing a newly formed vicinal tertiary and all‐carbon quaternary stereodyad. The utility of this protocol is further demonstrated via a number of synthetically diverse product transformations.     

Representation of Multicomponent Liquid-Liquid Equilibria for Aqueous and Organic Solutions Using a Modified UNIQUAC Model

A modified form of the UNIQUAC model is presented to accurately reproducebinary phase equilibria and ternary and quaternary liquid-liquid equilibria ofaqueous and organic solutions. The model gives a good representation in thereproduction of binary coexistence curves over a wide temperature range usingtemperature-dependent parameters and of binary vapor-liquid equilibria usingtwo binary energy parameters, and in the correlation of ternary and quaternaryliquid-liquid equilibria using ternary and quaternary parameters, in addition tobinary parameters. The quaternary calculated results are compared with thoseobtained from the modified Wilson and extended UNIQUAC models.     

A study of the globulins of cotton seeds XX. Stability of the quaternary structure of the 11S-globulin

The 11S-globulin has a complex stable quaternary structure in the formation of which three types of subunits participate. The aim of the work was to determine what forces form and stabilize the quaternary structure of this protein. The products of the maleylation and acetylation of the 11S-globulin and also the stability of the native 11S-globulin in the presence of ionic and nonionic detergents were investigated by disk electrophoresis. It was shown that hydrophobic interactions play a deciding role in the formation and stabilization of the quaternary structure of the 11S-globulin.     

Synthesis of (+/-)-thiohalenaquinone by iterative metalations of thiophene

The synthesis of a thiophene-containing analogue of halenaquinone was realized. Key steps include an alkynyl ketone-benzocyclobutane Diels-Alder reaction to construct the C,D-ring naphthalene subunit, a Heck cyclization to form the quaternary carbon, and a ring closing metathesis to add the A-ring.     

Formation of gas-phase clusters monitored during electrospray mass spectrometry: a study of quaternary ammonium pesticides

Gas-phase cluster formation between the quaternary ammonium pesticides paraquat, diquat, difenzoquat, chlormequat and mepiquat, and chloride and acetate anions present in a liquid chromatography (LC) mobile phase, has been studied using electrospray mass spectrometry. The clusters of paraquat, mepiquat and chlormequat were revealed over the entire m/z range of the mass spectrometer, and their formation is dependent on the concentrations of both the cationic and the anionic species. Mepiquat and chlormequat form clusters of the type [2M(q)(+) + A(-)](+), where M(q)(+) is the quaternary ammonium cation and A(-) is the anion. Paraquat forms a cluster species with ammonia and also an ion-pair complex with chloride anions. Diquat and difenzoquat did not form observable ion-pair complexes or clusters with any of the anions studied. Competitive binding of acetate and chloride anions reflects the higher charge density of chloride, which forms the dominant clusters with mepiquat and chlormequat. The formation of cluster species has implications for the quantification of quaternary ammonium pesticides and may have an influence on the linearity of calibrations.     

Synthesis of the ring system of phomactin D using a Suzuki macrocyclization

[reaction: see text]The ring system of phomactin D was synthesized in racemic form in an efficient manner from 2,3-dimethylcyclohexanone. Notable transformations include (1) an alkylation of the enolate of a vinylogous thiolester to install a quaternary stereocenter, (2) a conjugate addition of cyanide to an alpha,beta-unsaturated aldehyde, (3) the formation of a Weinreb amide directly from a cyanohydrin, and (4) an intramolecular Pd-mediated Suzuki coupling of a B-alkyl-9-BBN derivative and a vinyl iodide to form the macrocyclic ring.     

Unexpected Hofmann elimination in the benzophenone-(phenylthio)acetic tetrabutylammonium salt photoredox system

The triplet state of benzophenone was quenched by the tetrabutylammonium salt of (phenylthio)acetic acid in acetonitrile solutions. The quenching event, following laser flash photolysis, resulted in the formation of a transient ion pair consisting of the benzophenone radical anion and the tetrabutylammonium cation. Subsequently this ion pair decays with the quaternary ammonium cation undergoing a Hofmann elimination to form butane-1 and tributylamine, which were detected in steady-state irradiation. This appears to be the first report of an ion pair consisting of a benzophenone radical anion and an organic cation (nonradical), in addition to the first report of a photoinduced Hofmann elimination in quaternary ammonium ions.     

The catalytic asymmetric total synthesis of elatol

Described in this report is the first total synthesis of elatol, a halogenated sesquiterpene in the chamigrene natural product family. The key disconnections in our synthetic approach include an enantioselective decarboxylative allylation to form the all-carbon quaternary stereocenter and a ring-closing olefin metathesis to concomitantly form the spirocyclic core as well as the fully substituted chlorinated olefin. This strategy represents a general platform for accessing the chamigrene natural product family, as demonstrated by the synthesis of (+)-laurencenone B as an intermediate in our route.     

Trapping specific quaternary states of the allosteric enzyme aspartate transcarbamoylase in silica matrix sol-gels

The extreme T and R quaternary structures of the allosteric enzyme aspartate transcarbamoylase have been trapped by encapsulation in a silica sol-gel matrix. Detection of the specific quaternary structure present in the sol-gel was accomplished using a pyrene-labeled version of the enzyme that exhibited monomer fluorescence in the T quaternary structure and excimer fluorescence in the R quaternary structure. Using thin films of the encapsulated enzyme, kinetics of the T and R states could be determined without interconversion of the states. Using a monolith form of the encapsulated enzyme, the transition from the T or the R structure was monitored. Within the sol-gel matrix, the rate of the transition was slowed approximately 105 over that observed in solution.     

First enantioselective total synthesis of (+)-(R)-Pinnatolide using an asymmetric domino allylation reaction

An efficient total synthesis of (+)-(R)-Pinnatolide is described. As a key step an asymmetric multicomponent domino allylation reaction of methyl levulinate is used to form the quaternary stereogenic center in a highly selective way.     

Rhodium-catalyzed cross-coupling reaction of arylboronates and diazoesters and tandem alkylation reaction for the synthesis of quaternary α,α-heterodiaryl carboxylic esters

A rhodium-catalyzed one-pot three-component coupling reaction was developed for the synthesis of quaternary α,α-heterodiaryl carboxylic esters. This reaction involves cross-coupling of the arylrhodium(I) complexes with α-aryldiazoacetates to form oxa-π-allylrhodium complexes. With KOtBu and alkyl halides, tandem alkylation of the allyl complex occurs to form a quaternary stereocenter at the carbenic carbon.     

Synthesis,Properties, and Application of Cationic Reactive Disperse Dyes Containing Quaternary Group

A series of cationic reactive disperse dyes containing quaternary group were synthesized. The dyeing behavior of these dyes on wool was studied. The results show that cationic reactive disperse dyes containing quaternary group is available to form covalent bond with nucleophiles in the wool even under acidic condition. The fastness on wool was excellent.     

Electrophilic C12 building blocks for alkaloids: formal total synthesis of (+/-)-maritidine

Silyl-protected benzyl alcohol derivatives and the salt 1 are used to form ortho-substituted C12 electrophilic organoiron building blocks which are converted into a spirocyclic cyclohexenone to complete a formal total synthesis of (+/-)-maritidine (5). The choice of TBDPS protection was shown to be better than TIPS and compatible with ipso nucleophile addition to form a quaternary center. The reaction sequence is the first example of a successful application in the synthesis of an arylcyclohexadienyliron complex with an ortho-carbon substituent in the position required for Amaryllidaceae alkaloids of this type.     

Oxidative N-Heterocyclic Carbene Catalyzed Dearomatization of Indoles to Spirocyclic Indolenines with a Quaternary Carbon Stereocenter

An efficient method for the asymmetric intramolecular dearomatization of indoles by using oxidative N-heterocyclic carbene catalysis is demonstrated. Valuable optically active spirocyclic indolenines bearing an all-carbon quaternary stereocenter are obtained in excellent yields and with excellent enantioselectivity. The starting indoles are readily prepared and the reactions proceed through an intramolecular indole 3-acylation with an in situ generated acyl azolium intermediate to form a spirocyclic ketone moiety.     

Enantioselective Formation of All‐Carbon Quaternary Stereocenters from Indoles and Tertiary Alcohols Bearing A Directing Group

Described is an efficient catalytic asymmetric intermolecular C? C bond‐formation process to generate acyclic all‐carbon quaternary stereocenters. The reactions overcome the unfavorable steric hindrance around reactive centers, and the competitive elimination (E1), to form a range of useful indole products with excellent efficiency and enantioselectivity.