An alternative role for acetylenes: activation of fluorobenzenes toward nucleophilic aromatic substitution.

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.

Single step synthesis of acetylene-substituted oxacalix[4]arenes.

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.