Synthesis and 1H NMR structural analysis of 11-aryl/heteroarylnaphtha[2,1-b]furans: X-ray crystal structure of 11-(4′-pyridyl)naphtho[2,1 -b]furan

Synthesis of biaryl type systems, 11‐aryl/heteroarylnaphtho[2,1‐b]furans 8‐11 has been described with a view to studying the conformational orientation of C‐11 aryl/heteroaryl groups. Synthesis of 8‐11 was accomplished by a two‐step sequence involving O‐alkylation of 2‐naphthol with appropriate halo‐ketones 2‐4, followed by cyclization of the resulting naphthoxy‐ketones 5‐7 with methanesulphonic acid. The structures of 8‐11 are based on detailed 2D NMR spectral analysis. The H8 in these compounds is not subject to significant anisotropic upfield shielding effects. The slightly upfield chemical shift of H8 in molecules 9‐11, relative to 8 has been correlated with the electron density at C17 and C8 positions. While molecular modeling indicated dihedral angle (φ) between the C11 aryl/heteroaryl groups and the naphthofuran plane to be in the range of 70–60° in 8‐10, a single X‐ray crystal structural analysis of 11‐(4′‐pyridyl)naphtho[2,1‐b]furan 10 indicated (φ) of 64.36°. In view of significant deviations from the orthogonal oreintation, the absence of any significant anisotropic shielding in 8‐11 is not entirely unexpected.