RESUMO
A novel macrocyclic host molecule was synthesized that forms in a single step from commercially available starting materials. The core of the macrocycle backbone possesses two quinone rings and, thus, it is redox-active. Host-guest binding involving the clip-shaped cavity indicates selective binding of pyridine N-oxides based on the electron density of and steric bulk around the anionic oxygen.
RESUMO
Acetylenes are increasingly versatile functional groups for a range of complexity-building organic transformations and for the construction of desirable molecular architectures. Herein we disclose a previously underappreciated aspect of arylacetylene reactivity by utilizing alkynes as electron-withdrawing groups (EWG) for promoting nucleophilic aromatic substitution (S(N)Ar) reactions. Reaction rates for the substitution of 4-(fluoroethynyl)benzenes by p-cresol were determined by (1)H NMR spectroscopy, and these rate data were used to determine substituent (Hammett) constants for terminal and substituted ethynyl groups. The synthetic scope of acetylene-activated S(N)Ar reactions is broad; fluoroarenes bearing one or two ethynyl groups undergo high-yielding substitution with a variety of oxygen and arylamine nucleophiles.
RESUMO
Trialkyl phosphites ((RO)3P) can act as co-initiators for the diaryliodonium-induced cationic polymerization of cyclohexene oxide (CHO) or THF. A radical initiation step is also required, consistent with the essential role of a radical chain reaction of the phosphite with the iodonium salt to form polymerization-starting aryltrialkoxyphosphonium salts (ArP(+)(OR)3). We used the visible photolysis of phenylazoisobutyronitrile (PAIBN) as the radical initiation step. The presence of multiple fluorine substituents on the phosphite, as in tris(2,2,2-trifluoroethyl) phosphite (TFP), allows polymerization to proceed with a minimal amount of chain transfer from nucleophilic attack by the phosphite. In a typical experiment, a CHO solution of bis(4-tert-butylphenyl)iodonium hexafluorophosphate (0.05 M), TFP (0.1 M), and PAIBN (0.02 M) was illuminated with a 65-W compact fluorescent bulb for 1 h, resulting in a 78% conversion to poly(cyclohexene oxide) with an average molecular weight (MW) of 25000. We also used competition experiments to determine approximate rate constants for reactions of phenyl radicals with CHO (k = 2 × 10(6) M(-1) s(-1)) and with TFP (k = 2 × 10(8) M(-1) s(-1)).
RESUMO
Oxacalixarenes bearing acetylene groups are synthesized in a single step by nucleophilic aromatic substitution reactions of orcinol with various 1,5-diethynyl-2,4-difluorobenzenes. Thermodynamic equilibration of the cyclooligomer mixtures was accomplished for arylethynyl activating groups, leading to increased yields of the corresponding oxacalix[4]arenes. A 1,3-alternate macrocycle conformation is observed in the solid state, presenting a large V-shaped π-surface.
RESUMO
We describe a plasmonic crystal device possessing utility for optically transducing chemical forces. The device couples complex plasmonic fields to chemical changes via a chemoresponsive, surface-bound hydrogel. We find that this architecture significantly enhances the spectroscopic responses seen at visible wavelengths while enabling capacities for sensitive signal transduction, even in cases that involve essentially no change in refractive index, thus allowing analytical detection via colorimetric assays in both imaging and spectroscopic modes.