title: Mechanism and Dynamics of Intramolecular C-H Insertion Reactions of 1-Aza-2-azoniaallene Salts.
abstract: The 1-aza-2-azoniaallene salts, generated from α-chloroazo compounds by treatment with halophilic Lewis acids, undergo intramolecular C-H amination reactions to form pyrazolines in good to excellent yields. This intramolecular amination occurs readily at both benzylic and tertiary aliphatic positions and proceeds at an enantioenriched chiral center with retention of stereochemistry. Competition experiments show that insertion occurs more readily at an electron-rich benzylic position than it does at an electron-deficient one. The C-H amination reaction occurs only with certain tethers connecting the heteroallene cation and the pendant aryl groups. With a longer tether or when the reaction is intermolecular, electrophilic aromatic substitution occurs instead of C-H amination. The mechanism and origins of stereospecificity and chemoselectivity were explored with density functional theory (B3LYP and M06-2X). The 1-aza-2-azoniaallene cation undergoes C-H amination through a hydride transfer transition state to form the N-H bond, and the subsequent C-N bond formation occurs spontaneously to generate the heterocyclic product. This concerted two-stage mechanism was shown by IRC and quasi-classical molecular dynamics trajectory studies.
authors.affiliation: †Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States.
authors.forename: Xin
authors.initials: X
authors.lastname: Hong
authors.affiliation: ‡Department of Chemistry, The University of Vermont, Burlington, Vermont 05405, United States.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Bercovici
authors.affiliation: †Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States.
authors.forename: Zhongyue
authors.initials: Z
authors.lastname: Yang
authors.affiliation: ‡Department of Chemistry, The University of Vermont, Burlington, Vermont 05405, United States.
authors.forename: Nezar
authors.initials: N
authors.lastname: Al-Bataineh
authors.affiliation: ‡Department of Chemistry, The University of Vermont, Burlington, Vermont 05405, United States.
authors.forename: Ramya
authors.initials: R
authors.lastname: Srinivasan
authors.affiliation: ‡Department of Chemistry, The University of Vermont, Burlington, Vermont 05405, United States.
authors.forename: Ram C
authors.initials: RC
authors.lastname: Dhakal
authors.affiliation: †Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States.
authors.forename: K N
authors.initials: KN
authors.lastname: Houk
authors.affiliation: ‡Department of Chemistry, The University of Vermont, Burlington, Vermont 05405, United States.
authors.forename: Matthias
authors.initials: M
authors.lastname: Brewer
mesh_terms: D000466:Alkadienes / Q000737:chemistry*; D000586:Amination; D001372:Aza Compounds / Q000737:chemistry*; D001593:Benzyl Compounds / Q000737:chemistry; D008958:Models, Molecular; D011720:Pyrazoles / Q000737:chemistry; D012492:Salts / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000466:Alkadienes; D001372:Aza Compounds; D001593:Benzyl Compounds; D011720:Pyrazoles; D012492:Salts; C025947:propadiene