A new and versatile synthetic route for 8-oxoprotoberberine 17 through synthesis of isoquinolinone 16 and construction of a B-ring is described. The key step is the synthesis of isoquinolinone 14 through thermal cyclization of 2-alkynylbenzaldehyde oxime 12 to afford isoquinoline N-oxide 13, followed by a Reissert–Henze-type reaction. The first total synthesis of 8-oxoprotoberberine alkaloid alangiumkaloids A and B was achieved by using this strategy. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim