Direct Umpolung Morita-Baylis-Hillman like α-Functionalization of Enones via Enolonium Species.

Herein we report on the umpolung of Morita-Baylis-Hillman type intermediates and application to the α-functionalization of enone C-H bonds. This reaction gives direct access to α-chloro-enones, 1,2-diketones and α-tosyloxy-enones. The latter are important intermediates for cross-coupling reaction and, to the best of our knowledge, cannot be made in a single step from enones in any other way.

A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species.

α-Functionalization of ketones via umpolung of enolates by hypervalent iodine reagents is an important concept in synthetic organic chemistry. Recently, we have developed a two-step strategy for ketone enolate umpolung that has enabled the development of methods for chlorination, azidation, and amination using azoles. In addition, we have developed C-C bond-forming arylation and allylation reactions.

Cross-coupling of dissimilar ketone enolates via enolonium species to afford non-symmetrical 1,4-diketones.

Due to their closely matched reactivity, the coupling of two dissimilar ketone enolates to form a 1,4-diketone remains a challenge in organic synthesis. We herein report that umpolung of a ketone trimethylsilyl enol ether (1 equiv) to form a discrete enolonium species, followed by addition of as little as 1.2-1.

α-N-Heteroarylation and α-Azidation of Ketones via Enolonium Species.

Enolonium species, resulting from the umpolung of ketone enolates by Koser's hypervalent iodine reagents activated by boron trifluoride, react with a variety of nitrogen heterocycles to form α-aminated ketones. The reactions are mild and complete in 4-5 h. Additionally, α-azidation of the enolonium species takes place using trimethylsilyl azide as a convenient source of azide nucleophile.

Transition-Metal-Free Intermolecular α-Arylation of Ketones via Enolonium Species.

Herein it is shown, for the first time, that enolonium species are powerful electrophiles capable of reacting with aromatic compounds in an intermolecular manner to afford α-arylated ketones. The reaction is compatible with a variety of functional groups, is of wide scope with respect to aromatic compounds and ketone, and even works for polymerization-prone substrates such as substituted pyrroles, thiophenes, and furans. Only 1.