Cleavage, heterolytic intermolecular

One of the best examples of intermolecular heterolytic cleavage of r 2-H2 is the protonation of ethers by extremely electrophilic cationic H2 complexes containing electron-withdrawing ligands such as CO [Eqs. (6)—(7)] (32). 

Intermolecular heterolytic cleavage involves proton transfer to an external base to give a metal hydride (H- fragment) and the conjugate acid of the base, HB+. This... 

The vicinal hydroxyl group can be replaced by any function transformable to alkoxide under very basic conditions as, for example, acetate. More surprising is the obviously practical preparation starting from tron -ditosylates (reaction 7.4). This reaction occurs at 0°C, yet it involves heterolytic cleavage between the oxygen and sulfur atoms which is not at all simple to carry out by an intermolecular route. We can observe that the tosylate at C-3 is displaced leading to a-D-allo epoxide 7.18. Here again we see the inertia of position 2 relative to the substitution. 

Lewis acids can induce heterolytic cleavage of the ethereal bridge of 7-oxanorbomanes as exemplified with the cmiversion of 187 into 188 [237], and of 189 into 190 [238] that imply intermolecular quenching of the nucleophile, and for the intramolecular displacement of the ethereal bridge of 191 by its Al-benzylamido moiety to give the bicycUc lactam 192 with high stereoselectivity (Sivii displacement) [239] (Scheme 30). 

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