Kurzfassung

Abstract:
Aerobic oxidation of alkyl- and phenyl-substituted 4-pentenols (bishomoallyl alcohols), catalyzed by cobalt(II) complexes in solutions of -terpinene or cyclohexa-1,4-diene, stereoselectively gave tetrahydrofurylmethyl radicals. Cyclized radicals were trapped with monosubstituted olefins (e.g. acrylonitrile, methyl acrylate), (E)- and (Z)-1,2-diacceptor-substituted olefins (e.g. dimethyl fumarate, fumarodinitrile, N-phenyl maleic imide), and ester-substituted alkynes (e.g. ethyl...Abstract:
Aerobic oxidation of alkyl- and phenyl-substituted 4-pentenols (bishomoallyl alcohols), catalyzed by cobalt(II) complexes in solutions of -terpinene or cyclohexa-1,4-diene, stereoselectively gave tetrahydrofurylmethyl radicals. Cyclized radicals were trapped with monosubstituted olefins (e.g. acrylonitrile, methyl acrylate), (E)- and (Z)-1,2-diacceptor-substituted olefins (e.g. dimethyl fumarate, fumarodinitrile, N-phenyl maleic imide), and ester-substituted alkynes (e.g. ethyl propynoate). Oxidation-addition cascades thus furnished side chain-substituted (CN, CO2R, COR, or SO2R) di- and trisubsituted tetrahydrofurans in stereoselective reactions (2,3-trans, 2,4-cis, and 2,5-trans). A diastereomerically pure bistetrahydrofuran was prepared in a cascade consisting of two areobic oxidations, one alkyne addition, and one final H-atom transfer.

Conclusion:
The chemistry associated with the final step of cobalt-catalyzed aerobic alkenol oxidation, in conclusion, is uncontradictively explicable with the existence of free carbon radicals. If combinations of XH-acidic nucleophiles (X = e.g. O, N) and olefines other than those described in the present report were able to provide free carbon radicals, the new methodology would have the potential to usefully supplement existing well-established tin- or silicon hydride-based methods for conducting carbon radical chemistry under reductive conditions.

Leading References:
[1] Functionalized Tetrahydrofurans from Alkenols and Olefins/Alkynes via Aerobic Oxidation-Reductive Radical Addition Cascades. P. Fries, J. Hartung, J. Am. Chem. Soc. 2011, DOI:10.1021/ja108403s.
[2] Reductive and Brominative Termination of Alkenol Cyclization in Aerobic Cobalt-Catalyzed Reactions. D. Schuch, P. Fries, M. Dönges, J. Hartung, J. Am. Chem. Soc., 2009, 131, 12918–12920.
[3] Cobalt-Catalyzed Aerobic Oxidation of (E)- and (Z)-Bishomoallylic Alcohols. B. Menéndez Pérez, J. Hartung, Tetrahedron Lett. 2009, 50, 960–962. DOI: 101016j.tetlet.2008.12040.
[4] Chlorobis(dimethylglyoximato)(pyridine)cobalt(III), B. Menéndez Pérez, J. Hartung in Reagents for Radical Chemistry – Encyclopedia of Reagents in Organic Chemistry (Hrsg. D. Crich), John Wiley & Sons, New York, N.Y., 2008, 166–174. DOI:10.1002/047084289X.rc074m.
[5] Activation of Molecular Oxygen and its Use in Stereoselective Tetrahydrofuran-Syntheses from d,e-Unsaturated Alcohols, B. Menéndez Pérez, D. Schuch, J. Hartung, Org. Biomol. Chem. 2008, 6, 3532–3541.
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