Generation of a Carbanion y to the Carbon-Oxygen Bond

The generation of a carbanion gamma to the oxygen bridgehead could also lead to elimination and ring opening. Arjona and co-workers explored this strategy 

It is particularly difficult to carry out a ring opening in compounds containing the oxabicyclo[2.2.1] nucleus without concomitant aromatization, because the strong acidic conditions can also lead to dehydration. On the other hand, inducing aromatization under controlled conditions permits the synthesis of highly-substituted aryl compounds as an alternative synthetic strategy to traditional electrophilic aromatic substitution . The methods to aromatize oxabicyclo [2.2.1 ] heptanyl derivatives by the use of acids and low valent metals have been reviewed [172]. 

For the heterolytic cleavage of the bridging ether in oxabicyclo[3.2.1] substrates, it is essential to find reaction conditions to induce a regioselective opening, as well as complementary conditions selective for troponization, in light of the biological activity of many troponoids. 

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