K+‐Mediated vs Pd‐Catalyzed Cyclotrimerization of 9,10‐Didehydrotribenzo[8]annulene (TribenzoCOTyne): Stereodivergent Access to (α,α,α)‐ and (α,α,β)‐Fragments of Cubic Graphite

Abstract A remarkable stereodivergent cyclotrimerization of 9,10‐didehydrotribenzo[8]annulene (tribenzoCOTyne) to the corresponding (α,α,α)‐ and (α,α,β)‐benzofused derivatives has been developed by controlling the reaction conditions. While the K + ‐mediated cyclotrimerization afforded the (α,α,α) stereoisomer, using Pd as a catalyst resulted in the (α,α,β)‐derivative. Both stereoisomers were evidenced by spectroscopic data and crystal X‐Ray analysis. The (α,α,α) stereoisomer is a fragment of cubic graphite (CG), an elusive 3D carbon allotrope that contains carbon cages, since all of its sixty carbons are part of the structure of CG, and 36 constitute a part of the C 48 molecular cage of CG. Experimental and computational mechanistic studies revealed that the potassium ion would play a key role as a template to favor the formation of the (α,α,α) stereoisomer.