Synthesis of Isochromanones
An easily prepared recyclable TEMPO derived sulfonic salt catalyst, and mineral acids (NaNO2 and HCl) enable a selective aerobic oxidation of structurally diverse benzylic sp3 C-H bonds of ethers and alkylarenes to provide synthetically and biologically valued isochromanones and xanthones in good yields.
Z. Zhang, Y. Gao, Y. Liu, J. Li, H. Xie, H. Li, W. Wang, Org. Lett., 2015, 17, 5492-5495.
A cyanide-catalyzed ring-expansion of cyclic α-hydroxy-β-oxoesters provides δ-valerolactone derivatives in up to quantitative yields. Several alkyl-substituted as well as benzo- and heteroarene-annulated starting materials are converted without problems. As an additional benefit, the substrates are straightforwardly accessed by cerium-catalyzed aerobic α-hydroxylation of readily available β-oxoesters.
D. Kieslich, J. Christoffers, Org. Lett., 2021, 23, 953-957.
A highly stereoselective one-pot intramolecular Mannich reaction using 2-oxopropyl-2-formylbenzoates and anilines as substrates, catalyzed by a secondary amine, provides 4-aminoisochromanones bearing two adjacent stereocentres in good yields with excellent cis-stereoselectivities and ee values.
F. Vetica, J. Fronert, R. Puttreddy, K. Rissanen, D. Enders, Synthesis, 2016, 48, 4451-4458.