Synthesis of novel acetylenic cyclophanes with helical chirality: potential new structures for liquid crystals

Planar Chiral p,p'-Terphenyl-Based Cyclophanes with Remarkable Enantiomer Stability: Synthesis, Theoretical Investigations, and Complexation Studies

Design of conformationally stable compounds with planar chirality is a topic of great interest mainly because of their potential applications as enantioselective ligands or other functional materials. Herein, we present the design and synthesis of novel planar chiral cyclophanes, obtained by ortho, ortho″ anchoring of the p,p'-terphenyl unit, with bridges of different lengths and rigidities, along with their nuclear magnetic resonance, mass spectrometry, and X-ray characterizations. We investigated the influence of the structural particularities of the bridges over the stability of the enantiomers, by means of nuclear magnetic resonance and chiral high-performance liquid chromatography as well as by density functional theory calculations. We also demonstrated the ability of one of the cyclophanes to preferentially bind arginine with Ka > 110 M-1 (ΔG > -11 kJ mol-1) in acetonitrile solutions containig 10 % water, in the presence of other amino acids.

Preparation of shape-persistent macrocycles with a single pyridine unit by double cross-coupling reactions of aryl bromides and alkynes

A double Sonogashira-type coupling reaction between aryl bromides and alkynes using a catalytic Pd/XPhos (2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl) system was introduced as an efficient method for the synthesis of shape-persistent macrocycles (SPMs). This approach is advantageous in the synthesis of SPMs with a single pyridine unit.

Phane Properties of [2.2]Paracyclophane/Dehydrobenzoannulene Hybrids

A series of [2.2]paracyclophane/dehydrobenzo[14]annulene (PC/DBA) hybrids (hydrocarbons 5, 6, 9, 10 b, and 10 c), [2.2]paracyclophane/dehydro[14]annulene (PC/DA) hybrids (7 and 8) and suitable model systems (11, 12, and 33) has been synthesized. Comparison of the electronic absorption spectra in each series of compounds provides further insight into the global communication between the decks in the [2.2]paracyclophane unit.

Molecular folding of C60 acetylenic cyclophanes: pi-stacking of superimposed aromatic rings

[structure: see text] The syntheses of two distinct families of phenylyne helical cyclophanes with potential for organic materials are described. The meta-bonded atropisomers afford interesting bowtie-like and butterfly-like conformers from a palladium(0), copper-mediated coupling sequence. Molecular modeling revealed the contrasting stereochemistry in these systems from differential molecular folding pathways during cyclization. The interplanar separation of the superimposed aromatic rings is approximately 3.5 A.

Facile intramolecular cyclization in oxidative coupling of acetylenes linked to 1,3-positions of benzene: strained [12]metacyclophanedienetetrayne system

Oxidative coupling of ethynylpropellane linked to 1,3,5-position of a benzene core 3b did not give the cage dimer 2 but the dimer 4 having a strained [12]metacyclophanedienetetrayne system. The spectral and structural features of the novel ring system were revealed for the simple dibenzo derivative 6, which was also prepared efficiently by the intramolecular cyclization of the open-chain precursor.

[2.2]paracyclophane/dehydrobenzoannulene hybrids: transannular delocalization in open-circuited conjugated macrocycles

Enhanced global delocalization throughout the "stepped" π-electron systems of the [2.2]paracyclophane/dehydrobenzoannulene (PC/DBA) hybrids 1 and 2 is strongly suggested by a comparison of their electronic absorption spectra with those of model compounds with complete and interrupted classical aromatic delocalization. A distinct bathochromic shift (for 1) and greater absorption intensity at higher wavelengths (for 1 and 2) is observed versus the corresponding model hydrocarbons.

Functionalized macrocyclic ligands for use in supramolecular chemistry

The synthesis of three cross-conjugated macrocycles bearing pyridine functionality is described. The ability of two of these molecules, 5a and 5c, to behave as 4,4'-bipyridine mimics in self-assembly reactions is demonstrated by axial coordination to a metalloporphyrin. The directed coordinative ability of the pyridine rings ensures predictable self-assembly into well-ordered nanoscale systems, both in solution and the solid state. 1H, 13C, and HMQC NMR spectroscopic experiments and ESI MS have been used to characterize the supramolecular complexes in solution. X-ray crystallographic analysis of solid-state assemblies 7a and 7c provides insight into the scope and flexibility of these macrocyclic ligands as supramolecular building blocks. UV-vis and fluorescence spectroscopies provide a description of their electronic characteristics.

A novel strained undecadiyne cyclophane with interesting dienophilic character

[reaction: see text] Copper-mediated oxidative coupling of 3 afforded the strained product 4 from intramolecular cyclization rather than the triply bridged cyclophane 5 from dimerization. X-ray analysis of the bromo derivative 15 confirmed the distorted nature of the butadiyne bridge (bond angles 164.1 degrees and 153.4 degrees). The distortion in the strained triple bond is reflected in its cycloaddition reactivity. Cyclopentadiene and 1,3-cyclohexandiene afforded the new adduct macrocycles 16 and 17, respectively.

Rapid homogeneous-phase Sonogashira coupling reactions using controlled microwave heating

A microwave-enhanced, rapid and efficient homogeneous-phase version of the Sonogashira reaction is presented. It has been applied to the coupling of aryl iodides, bromides, triflates, and aryl chloride, as well as pyridine and thiophene derivatives with trimethylsilylacetylene. Excellent yields (80-95%) for substrates containing a large variety of substituents in different positions are obtained in 5-25 min.

Synthesis of acetylenic cyclophanes via intramolecular self-assembly: evidence of perfluorophenyl-phenyl quadrupole interactions in the solution state

Reported herein is an example of a solution-state cross-coupling cyclization with an outcome mediated by perfluorophenyl-phenyl electrostatic interactions.