Expanded Cyclotetrabenzoins.

Cyclobenzoins are shape-persistent macrocycles of interest in the preparation of optoelectronic and porous materials. New cyclotetrabenzoins derived from biphenyl, naphthalene, and tolane skeletons were synthesized using N-heterocyclic carbene-catalyzed benzoin condensation. Their preparation proceeded with different regioselectivity than that observed in the cyanide-catalyzed preparation of the parent cyclotetrabenzoin. Crystal structures of two new cyclotetrabenzoin acetic esters have been obtained. Alkyne groups of the tolane-based cyclotetrabenzoin were postsynthetically functionalized with Co2(CO)6 moieties.