Facile synthesis and characterization of indene-fused 4-methylcoumarins and an unexpected skeletal rearrangement via Pechmann condensation. Issue 22 (28th May 2020)

• Record Type: Journal Article
• Authors: Wu, Jie; Liu, Wei; Liang, Li; Gan, Ya; Xia, Shuang; Gou, Xiaojun; Sun, Xiaohua
• Is Part Of: Tetrahedron letters. Volume 61:Issue 22(2020)
• Publication Date: 2020-05-28
• Subjects: Fused coumarin -- Indeno[1, 2-g]coumarin -- Indeno[2, 1-g]coumarin -- Pechmann condensation -- Skeletal rearrangement; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tetlet.2020.151917
• Languages: English
• ISSNs: 0040-4039

Abstract

Graphical abstract: Highlights: The facile synthesis of indene-fused 4-methylcoumarins. The observation of a fluorene skeletal rearrangement during the Pechmann reaction. The differences between the photophysical properties of the indeno[1, 2- g ]coumarins and indeno[2, 1- g ]coumarins. Abstract: The Pechmann condensation of phenolic fluorenes with ethyl acetoacetate afforded indene-fused 4-methylcoumarins. In addition to the expected indeno[1, 2- g ]coumarin, a skeletal rearranged compound was obtained as a concomitant product when 9, 9-dimethyl-9 H -fluorene-2, 7-diol was utilized as the substrate. X-ray crystallography was used to identify the structures of the isomers. Photochemical and photophysical studies indicated that compared with the non-rearranged products, the skeletal rearranged isomers have red shifted absorption maxima and much higher fluorescence quantum yields. A mechanism involving two competitive pathways for the simultaneous production of isomers was proposed.