Enolonium Species-Umpoled Enolates.

Area of Science:

• Organic Chemistry
• Hypervalent Iodine Chemistry
• Synthetic Methodology

Background:

• Enolonium species/iodo(III)enolates are proposed intermediates in hypervalent iodine-mediated reactions of carbonyl compounds.
• These intermediates are crucial for various bond formations (α-C-O, α-C-N, α-C-C, α-carbon-halide) but have remained uncharacterized.
• Understanding these species is key to unlocking new synthetic pathways in organic chemistry.

Purpose of the Study:

• To synthesize and characterize elusive enolonium species (iodo(III)enolates) of carbonyl compounds.
• To provide the first spectroscopic evidence for these umpoled enolate intermediates.
• To demonstrate the role of enolonium species as direct intermediates in key bond-forming reactions.

Main Methods:

• Generation of enolonium species/iodo(III)enolates from carbonyl compounds under specific reaction conditions.
• Spectroscopic techniques (e.g., NMR, IR) for characterization of the transient intermediates.
• Reactions of isolated enolonium species with various allylic silanes (prenyl, crotyl, cinnamyl, allyl) to assess reactivity and selectivity.

Main Results:

• Enolonium species were successfully generated as discrete entities, stable for several minutes at -78°C.
• The first spectroscopic identification of these umpoled enolates was achieved.
• Enolonium species were confirmed as direct intermediates in C-O, C-N, C-Cl, and C-C bond formation.
• Reactions with allylic silanes exhibited absolute regioselectivity, yielding products in up to 92% yield.

Conclusions:

• The characterization of enolonium species provides concrete evidence for their role in hypervalent iodine chemistry.
• This work expands the chemical space for designing novel synthetic transformations involving carbonyl compounds.
• The demonstrated reactivity and selectivity of enolonium species open avenues for developing new synthetic methodologies.