Spontaneous formation of tricyclic lactones following the Castagnoli–Cushman reaction
Castagnoli–Cushman reaction of imines derived from 2-chloropyridine-3-carboxaldehyde with a cyclic anhydride (4-(methylsulfonyl)-morpholine-2,6-dione) conducted at 110°C in DMF over 1 h, as expected, led to a mixture of trans- and cis-configured carboxylic acids. However, the latter underwent a spontaneous intramolecular reaction of the carboxylic functionality onto the labile nearby 2-chloropyridine moiety to give the respective tricyclic lactones in 17–23% yield, along with 41–68% yield of the uncyclized trans-configured products (isolated as methyl esters).
Keywordstricyclic lactones-lactams Castagnoli–Cushman reaction intramolecular SNAr reaction post-MCR modification
This research was supported by the Russian Science Foundation (project grant 14-50-00069).
NMR, mass spectrometry and X-ray diffraction studies were performed at the Research Center for Magnetic Resonance, the Center for Chemical Analysis and Materials Research and the Center for X-ray Diffraction Methods of Research park of Saint Petersburg State University.