title: Aza- and Carbo-[3 + 3] Annulations of Exo-Cyclic Vinylogous Amides and Urethanes. Synthesis of Tetrahydroindolizidines and An Unexpected Formation of Hexahydroquinolines.
abstract: [3 + 3] Annulations of exo-cyclic vinylogous amides and urethanes with vinyl iminium salts are described here. We observed an intriguing dichotomy in their reaction pathways. For pyrrolidine- and azepane-based vinylogous amides or urethanes, aza-[3 + 3] annulation would dominate to give tetrahydroindolizidines, whereas, unexpectedly, for piperidine-based vinylogous amides or urethanes, carbo-[3 + 3] annulation was the pathway, leading to hexahydroquinolines. The origin for such a contrast is likely associated with a switch in the initial reaction pathway between C-1,2-addition and C-1,4-addition.
authors.affiliation: Division of Pharmaceutical Sciences and Department of Chemistry, 777 Highland Avenue, Rennebohm Hall, University of Wisconsin Madison, WI 53705 USA.
authors.forename: Sunil K
authors.initials: SK
authors.lastname: Ghosh
authors.forename: Grant S
authors.initials: GS
authors.lastname: Buchanan
authors.forename: Quincy A
authors.initials: QA
authors.lastname: Long
authors.forename: Yonggang
authors.initials: Y
authors.lastname: Wei
authors.forename: Ziyad F
authors.initials: ZF
authors.lastname: Al-Rashid
authors.forename: Heather M
authors.initials: HM
authors.lastname: Sklenicka
authors.forename: Richard P
authors.initials: RP
authors.lastname: Hsung