Enolonium Species: From Structure to New Reactivity
Prof. Alex M. Szpilman
Department of Chemical Sciences, Ariel University
Our group has developed a unique synthetic strategy involving the umpolung of enolates, which are
classically used as nucleophiles, through the action of hypervalent iodine to form electrophilic
enolonium species.1 These species, whose structures were controversial for over 40 years, have been
characterized using in situ NMR and IR spectroscopy.1a We have applied this strategy to a plethora of
new ketone α-functionalization reactions, including allylation,1a arylation,1b azidation,1c Nheteroarylation,
1c and cross-coupling with TMS enol ethers to give 1,4-dicarbonyl compounds.1d This
chemistry has also led us to develop new reactive intermediates such as azido-enolonium species.1e
As an aside, this chemistry also led to the serendipitous discovery of the nitro-cyclopropanation of
enones1f and the synthesis of indoline-3-ones.1g We have developed the first umpolung Morita–Baylis–
Hillman reaction, in which the key nucleophilic enolate intermediate of the classical Morita–Baylis–
Hillman reaction is inverted into an electrophilic enolonium species that can react with nucleophiles.2
This