THE PREPARATION AND SOME REACTIONS OF TRICYCLO(4.4.4.0)TETRADECANE‐2,7‐DIONE ((4.4.4)PROPELLANE‐2,7‐DIONE): X‐RAY CRYSTAL STRUCTURE OF 2,7‐BIS(TRIMETHYLSILYLOXY)TETRACYCLO(4.4.4.0.02,7)TETRADECANE