N-alkoxy-n-acylnitrenium ions in intramolecular aromatic addition reactions |
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| Institution: | 1. Chemistry Department, University of New England, Armidale, N.S.W. 2351 Australia;1. Faculty of Chemistry, University of Łódź, Tamka 12, 91-403 Łódź, Poland;2. Institute of General and Ecological Chemistry, Łódź University of Technology, Żeromskiego 115, 90-924 Łódź, Poland;1. A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov Street, 28, 119991 Moscow, Russia;2. A.V. Bogatsky Physico-Chemical Institute of the National Academy of Sciences of Ukraine, Lustdorfskaya Road, 86, 65080 Odessa, Ukraine;1. Beijing Institute of Pharmacology & Toxicology, 27 Tai-Ping Road, Beijing 100850, China;2. Duke University Medical Center, Box 2926, Surgical Oncology Research Facility, Durham, NC 27710, USA;3. Natural Products Research Laboratories, UNC Eshelman School of Pharmacy, University of North Carolina, Chapel Hill, NC 27599, USA;4. Chinese Medicine Research and Development Center, China Medical University and Hospital, Taichung, Taiwan;1. Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland;2. Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland |
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| Abstract: | N-alkoxy-N-acylnitronium ions are generated by treatment of N-alkoxy-N-cohloroamides with silver ions in ethereal solvents. These intermediates readily cyclise onto aromatic nuclei on alkozy side-chains to give benzoxazines and benzoxazepines and on the acyl side-chains to give γ, δ and ϵ benzolactams. Spirane products are formed by ipso addition When a 4-methoxy substituent ia present on the side-chain aromatic rings. The yields and regioselectivities of these reactions have been ascribed to different transition structures for cyclisation onto the acyl and alkoxy side-chains which involve respectively an exocyolic and endocyclic N-0 π-bond. Evidence for this exeptionally high π-bond character has been obtained from MNDO calculations which predict a π-bond order of 0.9 and a rotational barrier of 29.7 kcalmol-1 |
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