Exploiting the Multidentate Nature of Chiral Disulfonimides in a Multicomponent Reaction for the Asymmetric Synthesis of Pyrrolo[1,2‐a]indoles: A Remarkable Case of Enantioinversion

A new multicomponent coupling reaction for the enantioselective synthesis of pyrrolo[1,2‐a]indoles under the catalysis of a chiral disulfonimide is described. The high specificity of the reaction is a consequence of the multidentate character of the Brønsted acid catalyst. Insights from DFT calculations helped explain the unexpected high enantioselectivity observed with the simplest 3,3′‐unsubstituted binaphthyl catalyst as a result of transition‐state stabilization by a network of cooperative noncovalent interactions. The remarkable enantioinversion resulting from the simple introduction of substituents at 3‐ and 3′‐positions, the first reported example of this phenomenon in the context of binaphthalene‐derived Brønsted acid catalysis, was instead attributed to destabilizing steric interactions.     

Morphology of Imidazolium‐Based Ionic Liquids as Deposited by Vapor Deposition: Micro‐/Nanodroplets and Thin Films

The morphology of micro‐ and nanodroplets and thin films of ionic liquids (ILs) prepared through physical vapor deposition is presented. The morphology of droplets deposited on indium‐tin‐oxide‐coated glass is presented for the extended 1‐alkyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([C_nC₁im][Ntf₂]; n=1–8) series, and the results show the nanostructuration of ILs. The use of in‐vacuum energetic particles enhances/increases the nanodroplets mobility/coalescence mechanisms and can be a pathway to the fabrication of thin IL films.     

Fueter's theorem in discrete Clifford analysis

In this paper, we discretize techniques for the construction of axially monogenic functions to the setting of discrete Clifford analysis. Wherefore, we work in the discrete Hermitian Clifford setting, where each basis vector e_j is split into a forward and backward basis vector: . We prove a discrete version of Fueter's theorem in odd dimension by showing that for a discrete monogenic function f(ξ₀,ξ₁) left‐monogenic in two variables ξ₀ and ξ₁ and for a left‐monogenic P_k(ξ), the m‐dimensional function is in itself left monogenic, that is, a discrete function in the kernel of the discrete Dirac operator. Closely related, we consider a Vekua‐type system for the construction of axially monogenic functions. We consider some explicit examples: the discrete axial‐exponential functions and the discrete Clifford–Hermite polynomials. Copyright © 2015 John Wiley & Sons, Ltd.     

Polymer structure and the compensation effect of the diffusion pre-exponential factor and activation energy of a permeating solute

In the present work, the relation between the pre-exponential factor and the apparent activation energy of diffusion, ln D(0) = alpha + betaE(D), so-called compensation effect, is re-examined and critically discussed for diffusion of gases in rubbery and glassy polymers. In principle, the above equation could be derived from the enthalpy-entropy compensation in the framework of the transition state theory. However, one should consider the influence of the jump length term contained in the pre-exponential factor, which may be affected by permeating species and polymer properties. We found that parameter alpha depends on penetrant size and polymer properties, such as local chain mobility and free volume. This can be interpreted by the fact that the jump length is affected by both penetrant and polymer properties. Finally, methods for estimating the jump length are discussed.     

Simultaneous distillation-extraction of high-value volatile compounds from Cistus ladanifer L

The present paper describes a procedure to isolate volatiles from rock-rose (Cistus ladanifer L.) using simultaneous distillation-extraction (SDE). High-value volatile compounds (HVVC) were selected and the influence of the extraction conditions investigated. The effect of the solvent nature and extraction time on SDE efficiency was studied. The best performance was achieved with pentane in 1 h operation. The extraction efficiencies ranged from 65% to 85% and the repeatability varied between 4% and 6% (as a CV%).The C. ladanifer SDE extracts were analysed by headspace solid phase microextraction (HS-SPME) followed by gas chromatography with flame ionization detection (GC-FID). The HS-SPME sampling conditions such as fiber coating, temperature, ionic strength and exposure time were optimized. The best results were achieved with an 85 μm polyacrylate fiber for a 60 min headspace extraction at 40 °C with 20% (w/v) of NaCl. For optimized conditions the recovery was in average higher than 90% for all compounds and the intermediate precision ranged from 4 to 9% (as CV %). The volatiles α-pinene (22.2 mg g⁻¹ of extract), 2,2,6-trimethylcyclohexanone (6.1 mg g⁻¹ of extract), borneol (3.0 mg g⁻¹ of extract) and bornyl acetate (3.9 mg g⁻¹ of extract) were identified in the SDE extracts obtained from the fresh plant material.     

Group 4 complexes of a new [OSSO]-type dianionic ligand. Coordination chemistry and preliminary polymerization catalysis studies

A straightforward synthesis of a new type of tetradentate dianionic [OSSO]-type ligand is described. This ligand features an ethylenedithiol core bridged via methylene groups to substituted phenols, thus representing an S analogue of the [ONNO]-type Salan ligands. The [OSSO]H2 ligand precursor reacted with titanium(IV) isopropoxide and with zirconium(IV) tert-butoxide to give the corresponding [OSSO]-M(OR)2 complexes, which formed as single C2-symmetric isomers but were fluxional according to variable-temperature NMR. An X-ray structure of [OSSO]-Zr(O-t-Bu)2 supported the fac-fac wrapping mode of the ligand. The dibenzyl complex [OSSO]-Zr(bn)2 that was obtained by a reaction between the ligand precursor and tetrabenzylzirconium was found to be an active 1-hexene polymerization catalyst upon activation with B(C6F5)3, leading to a stereoirregular polymer despite its C2 symmetry.     

Mixed unsymmetric oxadiazoline and/or imine platinum(II) complexes

Iminoacylation of acetone oxime Me(2)C[double bond, length as m-dash]NOH upon reaction with trans-[PtCl(2)(NCCH(2)CO(2)Me)(2)] and [2 + 3] cycloaddition of acyclic nitrone (-)O(+)N(Me) = C(H)(C(6)H(4)Me-4) to a nitrile ligand in lead to the formation of mono-imine trans-[PtCl(2)(imine-a)(NCCH(2)CO(2)Me)] [imine-a = NH[double bond, length as m-dash]C(CH(2)CO(2)Me)ON = CMe(2)] and mono-oxadiazoline trans-[PtCl(2)(oxadiazoline-a)(NCCH(2)CO(2)Me)] [oxadiazoline-a = [upper bond 1 start]N[double bond, length as m-dash]C(CH(2)CO(2)Me)ON(Me)C[upper bond 1 end](H)(C(6)H(4)Me-4)] unsymmetric mixed ligand complexes, respectively, as the main products. Reactions of or with acetone oxime , cyclic nitrone (-)O(+)N = CHCH(2)CH(2)C[upper bond 1 end]Me(2) or N,N-diethylhydroxylamine give access, in moderate to good yields, to the unsymmetric mixed ligand oxadiazoline and/or imine complexes trans-[PtCl(2)(oxadiazoline-a)(imine-a)] , trans-[PtCl(2)(oxadiazoline-a)(oxadiazoline-b)] [oxadiazoline-b = [upper bond 1 start]N[double bond, length as m-dash]C(CH(2)CO(2)Me)O[lower bond 1 start]NC[upper bond 1 end](H)CH(2)CH(2)C[lower bond 1 end]Me(2)], trans-[PtCl(2)(imine-a)(imine-b)] [imine-b = NH = C(CH(2)CO(2)Me)ONEt(2)] or trans-[PtCl(2)(imine-a)(oxadiazoline-b)] . The cis mono-imine mixed ligand complex cis-[PtCl(2)(imine-a)(NCCH(2)CO(2)Me)] is the major product from the reaction of cis-[PtCl(2)(NCCH(2)CO(2)Me)(2)] with the oxime , while the di-imine compound cis-[PtCl(2)(imine-a)(2)] is a minor product. Reaction of cis-[PtCl(2)(imine-a)(NCCH(2)CO(2)Me)] with N,N-diethylhydroxylamine or the cyclic nitrone affords, in good yields, the unsymmetric mixed ligand complexes cis-[PtCl(2)(imine-a)(imine-b)] or cis-[PtCl(2)(imine-a)(oxadiazoline-b)] , respectively. All these complexes were characterized by elemental analyses, IR and (1)H, (13)C and (195)Pt NMR spectroscopies, and FAB(+)-MS. The X-ray structural analysis of trans-[PtCl(2){NH=C(CH(2)CO(2)Me)ON=CMe(2)}(NCCH(2)CO(2)Me)] is also reported.     

Importance sampling algorithms for first passage time probabilities in the infinite server queue

This paper applies importance sampling simulation for estimating rare event probabilities of the first passage time in the infinite server queue with renewal arrivals and general service time distributions. We consider importance sampling algorithms which are based on large deviations results of the infinite server queue, and we consider an algorithm based on the cross-entropy method, where we allow light-tailed and heavy-tailed distributions for the interarrival times and the service times. Efficiency of the algorithms is discussed by simulation experiments.     

The Orthogonal Subcategory Problem and the Small Object Argument

A classical result of P. Freyd and M. Kelly states that in “good” categories, the Orthogonal Subcategory Problem has a positive solution for all classes of morphisms whose members are, except possibly for a subset, epimorphisms. We prove that under the same assumptions on the base category and on , the generalization of the Small Object Argument of D. Quillen holds—that is, every object of the category has a cellular -injective weak reflection. In locally presentable categories, we prove a sharper result: a class of morphisms is called quasi-presentable if for some cardinal λ every member of the class is either λ-presentable or an epimorphism. Both the Orthogonal Subcategory Problem and the Small Object Argument are valid for quasi-presentable classes. Surprisingly, in locally ranked categories (used previously to generalize Quillen’s result), this is no longer true: we present a class of morphisms, all but one being epimorphisms, such that the orthogonality subcategory is not reflective and the injectivity subcategory Inj is not weakly reflective. We also prove that in locally presentable categories, the injectivity logic and the Orthogonality Logic are complete for all quasi-presentable classes. Financial support by Centre for Mathematics of University of Coimbra and by School of Technology of Viseu is acknowledged by the third author.