Krenske EH, He S, Huang J, Du Y, Houk KN, Hsung RP. Intramolecular oxyallyl-carbonyl (3 + 2) cycloadditions.
J Am Chem Soc 2013;
135:5242-5. [PMID:
23544997 PMCID:
PMC3642281 DOI:
10.1021/ja312459b]
[Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Cycloadditions involving oxyallyl intermediates typically require an electron-rich diene or alkene, but we have discovered the first examples of the cycloaddition of heteroatom-stabilized oxyallyls onto carbonyl groups. An oxazolidinone-substituted oxyallyl undergoes chemoselective (3 + 2) cycloaddition onto the carbonyl group of a tethered dienone in preference to formation of the expected (4 + 3) cycloadduct. Density functional theory calculations indicated that the (3 + 2) cycloaddition takes place through a concerted, highly asynchronous mechanism. The transition state features simultaneous interactions of the oxyallyl LUMO with the carbonyl π and lone-pair orbitals, making this reaction "hemipseudopericyclic" (halfway between purely pericyclic and purely pseudopericyclic). Further (3 + 2) cycloadditions involving tethered phenyl ketones and a tethered enone were predicted theoretically and verified experimentally.
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