Bridgehead positions electrophilic substitution

In spite of the fact that the only a-protons with respect to the carbonyl group in the tricyclic y-keto esters 231 are at bridgehead positions and thus no real enolates can be formed [118], compounds 231 with R = OR could easily and selectively be deprotonated at C-7, and the resulting lithium derivative then substituted with various electrophiles (Scheme 66). 

Electrophilic substitution in isoxazoles occurs most readily in the 4-position. The latter is part of the ring junction in the fused systems and is only free in the N-bridgehead series. 

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