Cyclopentenones are present in a wide variety of biologically relevant natural products and act as intermediates in production of substituted cyclopentane derivatives. Allene oxides are precursors in the biosynthesis of cyclopentenones in plants and some marine life. Although these molecules act as potential links to synthetically available cyclopentenones, their cyclization behavior is not well understood. Recent work by Brash and Cha (J. Biol. Chem., 2013, 288, 20797) has suggested two interesting properties of studied allene oxides: their work proposed a novel Z-isomer and this isomer was capable of spontaneous cyclization competitive with hydrolysis, where hydrolysis dominated in the case of the E-isomer. To treat both open and closed shell rearrangement, calculations were run using CASSCF, ωB97xD, and CCSD(T), with up to the cc-pVTZ basis set with implicit solvation in isopropyl alcohol (DOI: 10.1039/C6OB00204H). The open shell pathway was found to be lower in energy than the closed shell pathway, forming a diradical oxyallyl intermediate. The diradical oxyallyl was able to interconvert between configurational isomers via a low energy cyclopropanone intermediate. The lowest energy pathway was found to form the experimentally observed cis-cyclopentenone.

Investigation of allene oxide to cyclopentenone cyclization mechanism through a diradical oxyallyl intermediate

252nd National Meeting (2016)

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