title: Mechanism, kinetics and selectivity of selenocyclization of 5-alkenylhydantoins: an experimental and computational study.
abstract: The mechanism and selectivity of a bicyclic hydantoin formation by selenium-induced cyclization are investigated. The proposed mechanism involves the intermediates formed by an electrophilic addition of the selenium reagent on a double bond of the starting 5-alkenylhydantoin prior the cyclization. These intermediates are readily converted into the more stable cyclic seleniranium cations. A key step of the mechanism is an intramolecular cyclization which is realized through an anti-attack of the internal nucleophile, the amidic nitrogen, to the seleniranium cation yielding the intermediate imidazolinium cations. Their deprotonation is followed by the formation of the fused bicyclic reaction products. Important intermediates and key transition states are studied by using density functional theory (DFT) methods. The pathways of the reaction are investigated in detail. There are two regioselective pathways related to 5-exo and 6-endo products. Theoretical calculations and the monitoring of the cyclization reaction using (1)H NMR spectroscopy are in a good agreement with the proposed mechanism and are consistent with our experimental results. The preferred pathway for formation of 5-exo products is confirmed.
authors.affiliation: Faculty of Science, University of Kragujevac, Radoja Domanovića 12 P.O. Box 60, 34000 Kragujevac, Serbia.
authors.forename: Biljana M
authors.initials: BM
authors.lastname: Šmit
authors.affiliation: Faculty of Science, University of Kragujevac, Radoja Domanovića 12 P.O. Box 60, 34000 Kragujevac, Serbia.
authors.forename: Radoslav Z
authors.initials: RZ
authors.lastname: Pavlović
authors.affiliation: Bioengineering Research and Development Center, 34000 Kragujevac, Serbia.
authors.forename: Dejan A
authors.initials: DA
authors.lastname: Milenković
authors.affiliation: Bioengineering Research and Development Center, 34000 Kragujevac, Serbia ; Department of Chemical-Technological Sciences, State University of Novi Pazar, Vuka Karadžića bb, 36300 Novi Pazar, Serbia.
authors.forename: Zoran S
authors.initials: ZS
authors.lastname: Marković
keywords: density functional theory; fused bicyclic hydantoins; intermediate; reaction mechanism; regioselectivity; selenocyclization