Intramolecular (4 + 2) cycloaddition of aryl-1-aza-2-azoniaallene salts: A practical approach to highly sterically-congested polycyclic protonated azomethine imines.

Autor: Dhakal RC; Department of Chemistry, The University of Vermont, 82 University Place, Burlington, VT 05405, United States., Brewer M; Department of Chemistry, The University of Vermont, 82 University Place, Burlington, VT 05405, United States.
Jazyk: angličtina
Zdroj: Tetrahedron [Tetrahedron] 2016 Jun 30; Vol. 72 (26), pp. 3718-3728. Date of Electronic Publication: 2016 Mar 21.
DOI: 10.1016/j.tet.2016.03.037
Abstrakt: We report an improved two-step reaction sequence that gives tricyclic protonated azomethine imine products containing a 1,2,3,4-tetrahydrocinnoline scaffold in high yield. This sequence involves the oxidation of aryl hydrazones with TFAA-activated DMSO to give the corresponding α-trifluoroacetoxyazo products, which react readily with TMSOTf to give 1-aza-2-azoniaallene salt intermediates that undergo intramolecular (4+2) cycloadditions with pendent alkenes. This reaction sequence is more general, more practical and more environmentally friendly than our initially reported method. The cycloaddition provides exceptionally sterically-hindered products in high yield.
Databáze: MEDLINE
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