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We report a sensitive method for comparing weak interactions between aryl rings located on the external surfaces of equilibrating homo‐ and heterodimeric capsules. Two identical self‐complementary resorcin[4]arene tetrabenzoate molecules and one tetramethylammonium cation form in CDCl3 hydrogen‐bonded homodimeric capsules whose exteriors are decorated with four tight pairs of weakly interacting aryl rings. The pair wise mixing of six different homodimers establishes their equilibria with the corresponding heterodimeric species in which two types of aryl rings exert on each other some gentle forces. This equilibrium is significantly shifted either towards homo‐ or heterodimers depending on the nature and location of the substituents in the weakly interacting aryl rings. The thermodynamic favorability or disadvantage of the heterodimerization is determined by stronger or weaker aryl‐aryl attractions in the hetero‐ or homodimeric capsules, respectively. The four‐fold amplification of weak aryl‐aryl interactions on the external surfaces of the equilibrating capsules is responsible for high sensitiveness of our approach. [ABSTRACT FROM AUTHOR]

A study of the fluorescence properties of dendrimers (GN is the dendrimer generation number) comprising of four varying luminophores , terphenyl (T), dansyl(D), stilbenyl(S) and eosin (E) is presented. The various mechanisms of fluorescence depolarization observed in the analysis, depending on the photophysical properties of the fluorescent units and structures of the dendrimers, are discussed.

The synthesis of 'designer' dendrimers and dendrons with sulfonlmide units at every branching point is reported. Two models branched oligosulfonimides are characterized in the solid state by single-crystal X-ray analysis and the reaction selectivities and conformation of sulfonimide branching points are rationalized by DFT calculations.

The Diels–Alder reaction of N -benzylcytisine with N -methyl- and N -benzylmaleimides is 100% endo -selective and gives the corresponding syn - and anti -diastereomers in 11–42% isolated yields. The studies of the reaction progress with LCMS and NMR along with detailed quantum chemical calculations revealed that some Diels–Alder adducts are kinetically and their isomers are thermodynamically controlled products. The Pd/C-catalyzed hydrogenation of benzyl-protected cytisine amine derivatives resulted in the removal of the benzyl group and the addition of hydrogen to the C=C double bond to give the corresponding secondary amines in 45–84% yield. The complete reduction of carbonyl groups in a cytisine derivative with LiAlH4 in THF under reflux afforded the respective tricyclic triamine. Quantum mechanical calculations for the mechanism of the Diels–Alder reaction between the simplest model compounds are presented. [ABSTRACT FROM AUTHOR]

The Prilezhaev epoxidation of N -Boc-protected 3-cyclobutylidenetropane 1a affords a 1:2 mixture of compounds 2a and 2b , in which tropane and cyclobutane fragments are spiro-connected to the oxirane ring in endo - and exo -fashion, respectively. The exo -isomer 2b is obtained in 89% yield and 97% selectivity via the dioxirane oxidation of 1a. BF3-catalyzed isomerization of exo -oxirane 2b results in a 1:1 mixture of the spirocyclic ketones endo 3a and exo 3b containing spiro-connected tropane and cyclopentanone rings, while endo -epoxide 2a gives exclusively endo -ketone 3a. Prilezhaev and dioxirane epoxidations of N -Boc-protected 3-cyclopropylidenetropane 1b affords a mixture of endo - and exo -oxiranes 2c and 2d. Compounds 2c and 2d are not isolated in individual forms since they isomerize into a mixture of spirocyclic ketones endo 3c and exo 3d. Removal of the Boc groups from ketones 3a – d gives the corresponding hydrochlorides of aminoketones 4a – d in quantitative yields. Quantum chemical calculations predict that the rearrangement of endo -epoxides into the corresponding endo -ketones involving BF3-containing intermediates has by 4.4–7.9 kcal/mol lower activation barriers than the respective conversion of the exo -epoxides into exo -ketones. The cyclopropyl-containing dispiroepoxides 2c and 2d are predicted to interconvert faster into the corresponding ketones compared to their less strained cyclobutyl counterparts 2a and 2b. [ABSTRACT FROM AUTHOR]

Research was conducted to examine the complexes of camphor enantiomers with alpha-cyclodextrin in D2O using 1H and 13C NMR spectroscopic methods. The complexes manifest splittings which were attributed to chiral recognition. Results demonstrate that both complexes displayed 1:2 stoichiometry using the Job method. Greater stability of the complex involving one enantiomer was reproduced using molecular dynamic simulations.

A study was conducted to analyze the preparation and conformational characteristics of C2v symmetrical resorcarene tetrasulfonates. Varian and Bruker instruments were utilized to determine the 1H and 13C nuclear magnetic resonance spectra. Results indicated the tetrasulfonates and tetraphosphates of resorcarenes as possible molecular platforms for the preorganization of different modules through the alteration of the hydroxy groups and unsubstituted resorcinol rings.

The regioselective formation of bis-benzoxazines 5/6 in 65%-86% yield was successfully achieved through the regioselective condensation of resorcarene tetratosylates. Nuclear magnetic resonance spectroscopy and single-crystal X-ray analysis verified the chiral, Csub(2)-symmetrical farmework of these compounds. Nis-benzoxazines 5f and 5i were observed to take on a boat-like conformation in crystalline state, where the two resorcinol, oxazine fragment-bearing rings are almost parallel.

Conformationally restrained exo -isomers of N -Boc-protected spiro[2′,2′-difluorocyclopropane-3′,2′-tropanes] were synthesized in 62–83% yield via absolutely diastereoselective cycloaddition of CF2 , generated in situ from Me3 SiCF3 /NaI in refluxing THF, to double bonds of 3-alkylidenetropanes. Standard removal of Boc protecting groups afforded corresponding exo -spiro[2′,2′-difluorocyclopropane-3′,2′-tropane] hydrochlorides in 82–94% yields. DFT and CCSD(T) calculations revealed that the observed exo -selectivity of difluorocarbene addition is likely to be caused by a lower activation barrier of the exo -difluorocyclopropanation compared to the endo -reaction. [ABSTRACT FROM AUTHOR]

The optimization of the repetitive steps involved in the synthesis of the sulfonimide-based dendrimers via systematic analysis of the persulfonylation of branched aromatic oligoamines with different arylsulfonyl chlorides is reported. The optimized method yielded the fourth generation N- and pentaphenylene-centered dendrimers with 16 and 32 peripheral groups.

The analysis of the potential stabilization of the normally unstable [C.sub.20], the smallest fullerene, via its encapsulation inside a tetraureacalix[4]arene dimer is discussed. The guest-free capsular dimer, which decomposes on a 1-ns time scale, is unstable but dimeric complexes with guests remained intact during the 5-ns simulation time, indicating the guest-driven formation of the molecular capsule.

Ab initio Hartree-Fock and density functional methods at the HF/6-31(d,p) and B3LYP/6-311-(d,p) levels, respectively being used for the comparative study of the relative stabilities of 17 multiply hydrogen-bonded complexes. This study shows that the stability information of the single complex could not be directly used to obtain stability data for hydrogen-bonded assemblies in general but it is noted that the geometry analysis of this can give useful insights into their cooperative effects affecting the complex stabilities.

A reply on the comment forwarded on rationalizing the strength of hydrogen-bonded complexes. Ab initio HF and DFT studies is presented. Clarification and explanation are forwarded in this study to verify the applicability of empirical rules.