Intramolecular oxyallyl-carbonyl (3 + 2) cycloadditions.

Area of Science:

• Organic Chemistry
• Reaction Mechanisms
• Cycloaddition Reactions

Background:

• Oxyallyl cycloadditions traditionally necessitate electron-rich dienes or alkenes.
• Previous methods lacked efficient pathways for oxyallyl intermediate reactions with carbonyl groups.

Purpose of the Study:

• To report the first cycloaddition of heteroatom-stabilized oxyallyls onto carbonyl groups.
• To investigate the chemoselectivity and mechanism of these novel cycloaddition reactions.

Main Methods:

• Utilized oxazolidinone-substituted oxyallyls and tethered dienones for cycloaddition experiments.
• Employed Density Functional Theory (DFT) calculations to elucidate the reaction mechanism.
• Verified theoretical predictions through experimental validation with phenyl ketones and enones.

Main Results:

• Demonstrated chemoselective (3 + 2) cycloaddition of an oxazolidinone-substituted oxyallyl onto a carbonyl group, overriding expected (4 + 3) adduct formation.
• DFT calculations revealed a concerted, highly asynchronous mechanism for the (3 + 2) cycloaddition.
• Identified the transition state as "hemipseudopericyclic" due to simultaneous oxyallyl LUMO interactions with carbonyl π and lone-pair orbitals.
• Experimentally confirmed predicted (3 + 2) cycloadditions with tethered phenyl ketones and enones.

Conclusions:

• Heteroatom-stabilized oxyallyls can undergo (3 + 2) cycloadditions with carbonyl groups, expanding the scope of oxyallyl chemistry.
• The reaction proceeds via a unique hemipseudopericyclic pathway, offering new mechanistic insights.
• This discovery provides a novel synthetic route with potential applications in organic synthesis.