Transition adamantanone with

Studies of adamantanone reduction have been interpreted by le Noble [8 a, 8 b, 9] as consistent with the Cieplak hypothesis, since the reaction occurs preferentially from the face opposite the more electron-rich cr-bond. The Cieplak hypothesis considers interactions of adjacent c-bonds adjacent to the transition state with the cr orbital of the forming C-Nu bond (see Fig. 6-18). Figure 6-19 shows that the mixing of the adjacent antiperiplanar C-D (D=donor) with the (7 c-nu ot the transition state lowers the energy of the transition state. 

It is of considerable interest to establish the magnitude of electronic effects on facial selectivity. The symmetry of 2-adamantanone (1 X=H) makes this structure ideal [61] to investigate electronic effects on transition state energy, since the faces of the carbonyl are little affected by steric and torsional effects with substitution at C5. The donor and acceptor ability of the four adjacent carbon-carbon bonds to the carbonyl can be varied without significantly altering the molecular structure. 

Figure 6-22. Transitions structure geometry for reduction of adamantanone (1 X=H) with AlHj.

Similarly, some cyclic ketals derived from 2-adamantanone were obtained in excellent yields thanks to microwave activation under solvent-free conditions [124] (Eq. 40). The important specific MW effect observed is consistent with mechanism considerations the dipolar transition state is more polar, and therefore more stabilized by the field than the ground state. 

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