Are Terminal Aryl Butadiynes Stable? Synthesis and X-ray Crystal Structures of a Series of Aryl- and Heteroaryl-butadiynes (Ar−C⋮C−C⋮C−H)

The synthesis and isolation are reported of a range of terminal aryl- and heteroaryl-butadiynes
(ArC⋮C−C⋮CH) 4a−h from 2-methyl-6-(aryl/heteroaryl)hexa-3,5-diyn-2-ol precursors. The stability
of 4a−h in solution is concentration dependent:  many of the derivatives can be stored as dilute solutions
for several days or even weeks. The X-ray crystal structures have been obtained for five ArC⋮C−C⋮CH
derivatives [Ar = 2-(9-fluorenonyl), 4-biphenyl, 2-pyridyl, 4-pyridyl, and 2-pyrazyl].