title: The rearrangement route to 2-azabicyclo[2.1.1]hexanes. Solvent and electrophile control of neighboring group participation.
abstract: The reactions of N-(alkoxycarbonyl)-2-azabicyclo[2.2.0]hex-5-enes 5 with halonium ion electrophiles were studied in polar and nonpolar aprotic solvents and also in protic media with the aim of controlling nitrogen neighboring group participation. Specifically, for bromonium ions nitrogen participation is facilitated by the polar aprotic solvent nitromethane and by the poorly nucleophilic protic solvent acetic acid. Alkene 5b and bromine/nitromethane afford only the rearranged anti,anti-5,6-dibromo-2-azabicyclo[2.1.1]hexane 6b, and NBS/acetic acid gives an 8:1 mixture favoring rearranged 5-bromo-6-acetate 6f. Conversely, pyridinium bromide perbromide/CH(2)Cl(2) is selective for only unrearranged 5,6-dibromide 7. Iodonium and phenylselenonium ions react with alkenes 5 to give only unrearranged 1,2-addition products 9 and 10, regardless of solvent. Chloronium and fluoronium ions react with alkenes 5 to give 4-aminomethyl-3-hydroxycyclobutene 11, derived by ring cleavage.
authors.affiliation: Department of Chemistry, Temple University, Philadelphia, Pennsylvania 19122, USA. grantkrow@aol.com
authors.forename: Grant R
authors.initials: GR
authors.lastname: Krow
authors.forename: Guoliang
authors.initials: G
authors.lastname: Lin
authors.forename: Deepa
authors.initials: D
authors.lastname: Rapolu
authors.forename: Yuhong
authors.initials: Y
authors.lastname: Fang
authors.forename: Walden S
authors.initials: WS
authors.lastname: Lester
authors.forename: Seth B
authors.initials: SB
authors.lastname: Herzon
authors.forename: Philip E
authors.initials: PE
authors.lastname: Sonnet