title: Intrinsic gas-phase reactivity of ionized 6-(oxomethylene)cyclohexa-2,4-dienone: evidence pointing to its neutral alpha-oxoketene counterpart as a proper precursor of various benzopyran-4-ones and analogues.
abstract: Despite its unique structure and potential use as an important building block in organic synthesis, the title alpha-oxoketene 1 has been formed mostly under very special conditions as a short-lived species. The reactivity of 1 is, therefore, nearly unexplored. In great contrast, it seemed that its ionized gaseous form 1*+ is stable and easily accessible. In this study, we used multiple-stage pentaquadrupole mass spectrometry to probe the formation of gaseous 1*+ and explore its stability and intrinsic reactivity. With water and methanol, gaseous 1*+ was found to react similarly to solvated 1, which indicates that there is a close parallel between their reactivities. Gaseous 1*+ was also found to react promptly via polar [3 + 2] cycloadditons with various dienophiles including alkenes, alkynes, isocyanates, ketones and esters, thus forming a series of benzopyran-4-ones (flavones, 4-chromanones, 4-chromenones, benzo[1,3]dioxin-4-ones, and analogues) that are common structural units in many natural products. The present availability of 1 at room temperature and the gas-phase findings reported herein for gaseous 1*+ indicate that solvated 1 should undergo many [4 + 2] cycloadditions and functions as a versatile precursor of a variety of biologically active molecules.
authors.affiliation: São Francisco University, Bragança Paulista 12916-900, São Paulo, Brazil.
authors.forename: Paulo Sergio
authors.initials: PS
authors.lastname: de Carvalho
authors.forename: Fabiane M
authors.initials: FM
authors.lastname: Nachtigall
authors.forename: Marcos Nogueira
authors.initials: MN
authors.lastname: Eberlin
authors.forename: Luiz Alberto Beraldo
authors.initials: LA
authors.lastname: Moraes
mesh_terms: D000475:Alkenes / Q000737:chemistry; D001578:Benzopyrans / Q000737:chemistry*; D002625:Chemistry, Organic / Q000379:methods*; D005030:Ethylenes / Q000737:chemistry*; D005740:Gases; D007659:Ketones / Q000737:chemistry*; D013058:Mass Spectrometry; D008956:Models, Chemical; D009930:Organic Chemicals / Q000737:chemistry; D011809:Quinones / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry
chemical_list: D000475:Alkenes; D001578:Benzopyrans; D005030:Ethylenes; D005740:Gases; D007659:Ketones; D009930:Organic Chemicals; D011809:Quinones; D012997:Solvents; C008223:ketene