A New Reactive Intermediate The Homoenolate Anion

This reaction includes a highly unusual epimerization of the C-6 carbon of I and a skeletal rearrangement in which the quaternary center of I ends up as the bridge C-7 carbon of product III. This, in turn, entails the formation of a bond between C-6 and C-2, as well as the rupture of the bond linking C-2 and C-l in compound I. 

Before going any further it is important to add that the parent hydrocarbon, camphane, does not undergo the slightest change when subjected to the same reaction conditions, so the homolytic abstraction of hydrogen at C-6 that would furnish free radical intermediates is highly unlikely. 

Careful deuterium exchange and mass spectral studies1,4 have also shown that proton abstraction in other carbons proximal—but not vicinal—to a ketone is also possible. The intermediacy of rather odd species like VII, which feature some of the strain character found in anti-Bredt alkenes and VIII, which nec- 

Alternatively, a structure much less demanding than V such as VII could also result by intramolecular monoalkylation of the copper carbenoid IV. This intermediate contains an electron deficient center two atoms removed from a carbonyl function. This is the combination required for acidic-type cleavages such as in /3-dicarbonyls and /3-keto esters. One would expect, therefore, the occurrence of the nucleophilic attack-bond fragmentation sequence represented in structure VIII to yield II. 

Both V and VII are highly unstable species, as is copper carbenoid IV. It is conceivable that both evolutionary alternatives follow downhill energy profiles.7 Whatever the particular mechanism, the transformation of I into II has been termed the vinylogous Wolff rearrangement,8 since it was taken as a homolog of the classical Wolff transposition. 

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