Aza- and Carbo-[3 + 3] Annulations of Exo-Cyclic Vinylogous Amides and Urethanes. Synthesis of Tetrahydroindolizidines and An Unexpected Formation of Hexahydroquinolines.
[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.
Ghosh
Sunil K
SK
Division of Pharmaceutical Sciences and Department of Chemistry, 777 Highland Avenue, Rennebohm Hall, University of Wisconsin Madison, WI 53705 USA.
Buchanan
Grant S
GS
Long
Quincy A
QA
Wei
Yonggang
Y
Al-Rashid
Ziyad F
ZF
Sklenicka
Heather M
HM
Hsung
Richard P
RP