Dodecamethoxy- and hexaoxotricyclobutabenzene: synthesis and characterization.

We report herein the syntheses of dodecamethoxytricyclobutabenzene (TCBB) 1 and hexaoxo-TCBB 2, a class of molecules with structural and theoretical interest. The preparation is based on the 3-fold [2 + 2] cycloadditions of benzyne and ketene silyl acetals (KSAs), where the selectively protected 2-iodophloroglucinol derivative served as a synthetic equivalent of benztriyne I, allowing rapid and regioselective annulation of fully functionalized four-membered rings. Structural study on the former compound showed that the C-C bond lengths in the central benzene ring were essentially the same.

Poly-oxygenated tricyclobutabenzenes via repeated [2 + 2] cycloaddition of benzyne and ketene silyl acetal.

Described herein is a synthesis of highly functionalized tricyclobutabenzenes, a class of molecules of structural and theoretical interest. The preparation is based on the repeated [2 + 2] cycloadditions of benzyne and ketene silyl acetals (KSAs), where two types of regioselectivity enable discrimination of the functionalities on the four-membered rings. By these steps, we were able to prepare poly-oxygenated octamethoxytricyclobutabenzene and its hydrolyzed tetra-oxo derivatives. Structural study on the latter compound showed the interesting properties related to the strained four-membered ring.

Strain-induced regioselectivities in reactions of benzyne possessing a fused four-membered ring.

[reaction: see text] A fused four-membered ring has a powerful directing ability in effecting the regioselective reactions of benzyne with ketene silyl acetal, nucleophile, and alpha-alkoxyfuran.