Centrohexaindanes bearing methyl groups in their molecular propellane cavities

The syntheses of two new centrohexaindane derivatives bearing methyl groups in their molecular propellane-type cavities are described. These new topologically non-planar hydrocarbons, 1,8-dimethylcentrohexaindane 6 and 1,4,8,28-tetramethylcentrohexaindane 7 were obtained from suitable 1,3-indanediones following the shortest aufbau strategy, the propellane route, representing a six-step access to these unusually highly condensed polycyclic hydrocarbons. X-ray single crystal structure analysis of 6 revealed that the presence of the two methyl groups in the cavities of the centrohexaindane framework does not give rise to significant distortion of the Td-symmetrical molecular skeleton; however, their efficient hiding within two of the four equivalent cavities allows for strong intermolecular disorder in the crystal.