Karthick M, Konikkara Abi E, Someshwar N, Anthony SP, Ramanathan CR. NaHSO
4/SiO
2 catalyzed generation of
o-quinone/
o-thioquinone methides: synthesis of arylxanthenes/ arylthioxanthenes
via oxa-6π-electrocyclization.
Org Biomol Chem 2020;
18:8653-8667. [PMID:
33073833 DOI:
10.1039/d0ob01868f]
[Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
ortho-Quinone methides, very reactive transient intermediates, are utilized successfully in synthesizing complex organic molecules of natural and biological significance. Among several synthetic protocols, the acid catalyzed generation of ortho-quinone methides from suitably substituted phenols is a promising method for further exploitation in organic synthesis. Such an interesting reactive species is conveniently employed in the synthesis of conformationally restricted triarylmethane derivatives such as 12/9-arylxanthenes/arylthioxanthenes starting from symmetrical/unsymmetrical 2-(hydroxydiarylmethyl)phenol/thiophenol, respectively, using SiO2-NaHSO4. Conformationally restricted 12/9-arylxanthenes/arylthioxanthenes were obtained in 52 to 96% yields using this protocol, which is believed to involve the formation of o-quinone methides followed by electrocyclic ring closure and isomerization at elevated temperature. Photophysical studies of selected examples in acidic media showed turn-on fluorescence by hydride ion transfer mediated π-conjugated xanthylium salt formation and suggested the application potential in bio-imaging and fluorescent sensors.
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