The interaction of organosilanes with triphenylmethyl tetrafluoroborate

Under mild conditions, Ph₃CBF₄ readily fluorinates the SiH bond(s) of trialkylsilanes and dialkylsilanes. The use of this reagent in the successful fluorination of HSiMe₂CH₂Fe(CO)₂Cp suggests that the reaction can be used to fluorinate silicon compounds that possibly would not survive more vigorous fluorination reactions. A convenient preparation of diorganofluorosilanes that have both hydrogen and fluorine bonded to silicon is described.     

Tandem base-promoted ring-opening/Brook rearrangement/allylic alkylation of O-silyl cyanohydrins of beta-silyl-alpha,beta-epoxyaldehyde: scope and mechanism

Metalated O-silyl cyanohydrins of beta-silyl-alpha,beta-epoxyaldehyde have been found to serve as functionalized homoenolate equivalents by a tandem sequence involving base-promoted ring opening of the epoxide, Brook rearrangement, and alkylation of the resulting allylic anion. On the basis of mechanistic studies involving competitive experiments using the diastereomeric cyanohydrins, we propose a reaction pathway involving a silicate intermediate 36 formed by a concerted process via an anti-opening of the epoxide followed by the formation of an O-Si bond.     

The nature and fragmentation pathways of the molecular ions of some arylureas,arylthioureas, acetanilides,thioacetanilides and related compounds

Evidence as to the nature of the molecular ions of the title compounds near the ionization thresholds and of their fragmentation processes is presented and discussed. The mode of formation of 5-membered rings, involving the loss of an ortho substituent, is compared and contrasted with the formally similar process reported for the N-dimethyl N'-(o-X-phenyl) formamidines.     

Mathematical simulation of propane dehydrogenation involving oxygen on an alumina-chromium catalyst promoted with Co,Ni, Bi,and K oxides

The rate laws of propane dehydrogenation involving oxygen on an alumina-chromium catalyst promoted with Co, Ni, Bi, and K oxides were studied. The reaction was carried out in a flow reactor in the temperature range of 560–640°C at residence times of 0.5–2.5 s. A kinetic model of the process according to a probable reaction scheme was proposed. The rate constants and activation energies of individual reactions that participate in the process were found. A mathematical model of the process was developed with consideration for material and heat balances and hydrodynamic conditions. The concentration and temperature fields and pressure along the height of the catalyst bed were calculated. The dependences of the target product yield and process selectivity on the residence time were plotted.     

Transition-metal-free O-, S-, and N-arylation of alcohols, thiols, amides, amines, and related heterocycles

A new protocol for the Ullmann-type arylation process of different aromatic heterocycles without any transition-metal catalyst, implying the use of a combination of an excess of potassium hydroxide and dimethyl sulfoxide, is described. The reaction can be performed between a broad range of starting nucleophiles including phenol, alcohols, amines, nitrogen-containing five-membered systems such as pyrazoles, imidazoles, and indoles, and amides with haloarenes, iodide and bromide derivatives giving the best results, the possible pathway involving the in situ generation of the corresponding benzyne intermediate. When the reaction was performed with 2-iodoaniline and either carboxamides or isothiocyanato derivatives, the corresponding benzoazole derivatives were obtained.     

Concise synthesis of spirocyclic, bridged gamma-butyrolactones via stereospecific, dyotropic rearrangements of beta-lactones involving 1,2-acyl and delta-lactone migrations

Dyotropic processes involving unprecedented 1,2-acyl migrations provide access to novel spirocyclic, bridged keto-gamma-lactones from a series of fused, tricyclic-beta-lactones, available via biscyclization of ketoacids including a new asymmetric variant. In addition, a spirocyclic bis-gamma-lactone was generated via a dyotropic process involving a 1,2-beta-lactone/sigma-lactone interchange. Overall, this sequence provides a simple, two-step process for conversion of diketoacids to complex spiro[5.n]alkanes bearing a contiguous tertiary carbon center, a quaternary carbon center, and a tertiary alcohol in the form of a bridging gamma-lactone.     

Synthesis of highly substituted benzene ring systems through three-component coupling of enyne imines,Fischer carbene complexes,and electron-deficient alkynes

Three-component coupling of Fischer carbene complexes, enyne aldehyde hydrazones, and electron-deficient alkynes leads to simple benzoate derivatives in a process involving the formation of an N-aminopyrrole derivative, Diels-Alder reaction, and nitrene extrusion. The products are readily converted into isoquinolones through reaction with primary amines. The reaction proceeds best with highly substituted and electron-rich pyrroles even though these are the sterically least favorable substrates, and this reactivity trend is supported by a computational study.     

Base-catalyzed domino reaction toward 3-benzylidenecyclohexenes: DBU-promoted sequential Michael, aldol, dehydration, and dealkoxycarbonylation

3-Benzylidenecyclohexene derivatives were prepared starting from the Baylis-Hillman adducts by using DBU-promoted domino process involving Michael, aldol, dehydration, and dealkoxycarbonylation.     

Discovery of a multi-bond forming, four-step tandem process: construction of drug-like polycyclic scaffolds

A one-pot tandem process involving an Overman rearrangement, ring closing enyne metathesis and a hydrogen bonding directed Diels-Alder reaction has been developed for the efficient diastereoselective synthesis of functionalised amino substituted tetralin and indene ring systems.     

A novel one-step approach for the preparation of alpha-amino acids,alpha-amino amides,and dipeptides from azetidine-2,3-diones

A remarkable reaction of azetidine-2,3-diones with primary as well as secondary amines, and water is presented. Simply by varying the nucleophile, an unprecedented one-step synthesis of alpha-amino acids, alpha-amino amides, and dipeptides, was developed in both the racemic and optically pure forms. The current mechanistic hypothesis invokes a concerted process involving CO extrusion. However, a stepwise pathway can also account for these novel transformations.     

Parallel Microflow Photochemistry: Process Optimization, Scale-up, and Library Synthesis

A novel, multimicrocapillary flow reactor (MμCFR) was constructed and applied to a series of sensitized photoadditions involving 2(5H)-furanones. The reactor allowed for rapid and energy-, time-, and space-efficient sensitizer screening, process optimization, validation, scale-up, and library synthesis.     

Azidosulfonylation of alkenes, dienes, and enynes

The radical mediated azidosulfonylation of various alkenes and alkynes that are able to undergo a rapid radical rearrangement is reported. For instance, treatment of 1,6-dienes or 1-en-6-ynes with benzenesulfonyl azide affords cyclic azidosulfones. High yields are observed when tertiary alkyl radicals are azidated in the last step of the cascade process. The azidosulfonylation of β-pinene involving ring opening of the bicyclic skeleton is also reported.     

Synthesis of new 4-aroyl-pyrano[c]chromenes via a one-pot,three-component reaction based on aryl glyoxals

A new library of pyrano[c]chromenes containing an aroyl group has been synthesized by a novel multicomponent process involving the reaction of various aryl glyoxals with 4-hydroxycoumarin and malononitrile. The reactions were catalyzed efficiently by ammonium dihydrogen phosphate to yield the desired products in good to excellent yields.     

Catalytic, enantioselective, conjugate alkyne addition

We document a copper-catalyzed, enantioselective, conjugate addition involving the direct use of a terminal acetylene, which undergoes in situ metalation. The addition reactions of phenylacetylene to Meldrum's acid derived acceptors take place in aqueous media, without recourse to inert atmosphere. The success of the enantioselective process was enabled by the use of a new class of conveniently accessed P,N-ligands, which we have termed PINAP. These modular ligands are responsive to numerous electronic and steric modifications that permit optimization of the reaction.     

Synthesis of symmetrical 1, 3-diynes via tandem reaction of (Z)-arylvinyl bromides in the presence of DBU and CuI

Microwave-assisted tandem reaction of(Z)-arylvinyl bromides involving an elimination and homocoupling in the presence of DBU and Cul in DMF affords a variety of symmetrical 1,3-diynes in good to excellent yields.This tandem process,eliminating the need of volatile and savory terminal alkynes,provides an alternative to the conventional homocoupling methods for the synthesis of symmetrical 1,3-diynes.     

Preparation and degradation of salts of poly(methacrylic acid)—Part II: Magnesium,calcium, strontium and barium salts

The thermal degradation behaviour of the alkaline earth metal polymethacrylates has been compared with that of the corresponding acetates and that of the alkali metal polymethacrylates, using thermal volatilisation analysis, thermogravimetry and analysis of the several product fractions and partially degraded polymer. The salt polymers resemble the acetates only in the order of their stabilities which increase with the size of the metal ion. Chain scission and depolymerisation, which was found to be an important process in the alkali metal polymethacrylate series, cannot occur to the same extent in the alkaline earth metal series because, except in the case of the magnesium salt, the monomers are involatile and cannot distil out of the reaction zone. The alternative process, involving formation of ketones and metal carbonate or oxide, therefore predominates. There is some evidence that chain scission occurs in the case of magnesium polymethacrylate. The mechanism of degradation is discussed.     

A new seeding and electroless approach to alloying,direct patterning,and self-forming barriers for Cu thin-film nanostructures

In contrast to the previous studies involving sputter deposition to form Cu-alloy thin films with several atomic percentages of incorporated metallic solutes, this work examines the feasibility of using electroless deposition in conjunction with a new site-selective seeding process for the alloying and direct patterning of Cu thin-film nanostructures on dielectric layers. Very minute amounts (0.4 at.%) of manganese can be incorporated into the constituting Cu and segregated to form an interfacial layer at the SiO₂/Cu interface upon annealing in an Ar–H₂ atmosphere. The interfacial layer made up of only a few atomic layers is identified based on synchrotron X-ray spectroscopy and serves as a barrier for advanced technology nodes.     

Domino pericyclic reactions of acyclic conjugated (E,Z,E,E)-tetraenes

Acyclic conjugated (E,Z,E,E)-tetraenes, upon thermolysis, undergo a domino pericyclic process involving 6π electrocyclisation of the (E,Z,E)-triene moiety to give the corresponding cis-disubstituted 5-vinyl-1,3-cyclohexadienes, followed by an intramolecular Diels-Alder reaction with the vinyl side chain to give tricyclo[3.2.1.0^2,7]oct-3-enes.     

Evidence for the intermediacy of arylbenzylnitrenium ions in the thermal rearrangement of isoxazolidines derived from C,N-diarylnitrones and 2-morpholin-4-yl-acrylonitrile

In contrast to the diaryl, dialkyl, alkylaryl, and parent series, nothing is known about the generation and chemical behavior of arylbenzylnitrenium ions. Herein, we report that these species can be generated by a process involving an unprecedented thermal rearrangement of isoxazolidines derived from C,N-diarylnitrones and 2-morpholin-4-yl-acrylonitrile. The products from these reactions are dramatically dependent upon the nature of the nitrone. Most of the observed chemistry originates from the singlet state.     

Multicomponent,Mannich-type assembly process for generating novel,biologically-active 2-arylpiperidines and derivatives

A multicomponent, Mannich-type assembly process commencing with commercially available bromobenzaldehydes was sequenced with [3+2] dipolar cycloaddition reactions involving nitrones and azomethine ylides to generate collections of fused, bicyclic scaffolds based on the 2-arylpiperidine subunit. Use of the 4-pentenoyl group, which served both as an activator in the Mannich-type reaction and a readily-cleaved amine protecting group, allowed sub-libraries to be prepared through piperidine N-functionalization and cross-coupling of the aryl bromide. A number of these derivatives displayed biological activities that had not previously been associated with this substructure. Methods were also developed that allowed rapid conversion of these scaffolds to novel, polycyclic dihydroquinazolin-2-ones, 2-imino-1,3-benzothiazinanes, dihydroisoquinolin-3-ones, and bridged tetrahydroquinolines.