Osmium-Catalyzed 7-endo Heterocyclization of Aromatic Alkynols into Benzoxepines

The wizard of Os: Regioselective osmium-catalyzed 7-endo heterocyclization of aromatic alkynols affords benzoxepines in good yields. The proposed catalytic cycle involves the key formation of osmium–vinylidene complexes via an alkynyl-hydride–osmium(IV) complex from the starting alkynol.We thank the MICINN (Spain) (CTQ2008-06557, CTQ2008-00810, Consolider Ingenio 2010 (CSD2007-00006)), Xunta de Galicia (2007/XA084 and INCITE08PXIB209024PR) and Diputación General de Aragón (E35). A.V-F. thanks USC and XUGA for a predoctoral grant. C.G-Y. thanks MICINN for a Ramón y Cajal research contract.Peer Reviewe