Katsuma Matsui, Yasutomo Segawa, and Kenichiro Itami

Org. Lett. 2012, ASAP. DOI: 10.1021/ol3005112

The first synthesis of a nitrogen-containing cycloparaphenylene, cyclo[14]paraphenylene[4]2,5-pyridylidene ([14,4]CPPy), has been achieved. A palladium-catalyzed stepwise assembly of 2,2′-bipyridine, benzene, and L-shaped cyclohexane units, followed by NaHSO₄/o-chloranil-mediated aromatization, successfully provided [14,4]CPPy. While the absorption and fluorescence properties of [14,4]CPPy were somewhat similar to those of cycloparaphenylenes (λ_abs = 344 nm, ε = 7.3 × 10⁴ cm^–1 M^–1, λ_em = 427 nm, Φ_F = 0.80), it was found that [14,4]CPPy possesses an interesting halochromic property.