Two‐Step Synthesis of Heptacyclo[6.6.0.02,6.03,13.04,11.05,9.010,14] tetradecane from Norbornadiene: Mechanism of the Cage Assembly and Post‐synthetic Functionalization

A selective and scalable two‐step approach to the dimerization of norbornadiene (NBD) into its thermodynamically most stable dimer, heptacyclo[6.6.0.02,6.03,13.04,11.05,9.010,14] tetradecane, (HCTD) is reported. Calculations indicate that the reaction starts with the Rh‐catalyzed stepwise homo Diels–Alder cyclisation of NBD into its exo‐cis‐endo dimer. Treatment of this compound with acid promotes its evolution to HCTD via a [1,2]‐sigmatropic rearrangement. The assemblies of 7,12‐disubstituted cages from 7‐(alkyl/aryl) NBDs, as well as the selective post‐synthetic C−H functionalization of the core HCTD scaffold at position C1, or positions C1 and C4 are described. Heptacyclotetradecane (HCTD) was synthesized through a two‐step process, which starts with the Rh‐catalyzed homo‐Diels Alder between two norbornadiene (nbd) units. Acidic treatment of the thus obtained intermediate affords the desired cage via sigmatropic rearrangement. The post‐synthetic functionalization of the HCTD scaffold is also described.