Homolytic vs Heterolytic Paths in the Photochemistry of Haloanilines
作者:Mauro Freccero、Maurizio Fagnoni、Angelo Albini
DOI:10.1021/ja036000r
日期:2003.10.1
calculations showing that in the presence of an ancillary molecule of water fragmentation is exothermic due to the formation of the strong H-F bond. The energy profile for both homo- and heterolytic dissociation paths has been mapped along the reaction coordinates in the gasphase and in acetonitrile. The conditions determining the efficiency and mode of dehalogenation have been defined. This is significant
Phenonium Ions from the Addition of Phenyl Cations to Alkenes. Photochemical Synthesis of (Rearranged) Aminoalkylanilines from Haloanilines in the Presence of Alkenes and Amines
photoheterolysis of the haloaniline, addition of the resulting phenyl cation to the alkene and trapping of the phenonium cation by amine. A fraction (up to ca. 20%) of aminoalkylanilines resulting from Wagner-Meerwein rearrangement of the phenonium cation is obtained in some cases. Reduction and direct trapping of the phenyl cation by the amine compete with the above three-component synthesis in a less stabilizing
sterochemistry of the addition across the alkene are best understood with a phenonium ion structure for the adduct. The nucleophile entering in beta can be varied under conditions in which the adductcation is trapped more efficiently than the starting phenyl cation. Thus, beta-methoxyalkylanilines are formed when the irradiation is carried out in methanol. beta-Iodoalkylanilines are obtained in acetonitrile
4'-diaminodiphenyls (via an intermediate cyclohexadienyl cation) or is reduced to the aniline (via the aniline radicalcation) in a ratio depending on the hydrogen-donating properties of the solvent. Transients attributable to the triplet aminophenyl cation as well as to the ensuing intermediates are detected. Chemical evidence for the generation of the phenyl cation is given by trapping via electrophilic substitution
2-(4-N,N-dimethylaminophenyl) heterocycles are smoothly obtained from the photolysis of 4-chloro-N,N-dimethylaniline in acetonitrile in the presence of furan, pyrrole, thiophene and some of their methyl derivatives bearing a free α-position. With 2,5-dimethyl heterocycles the arylation occurs with equal efficiency in the β position. In the case of furan, when the irradiation is carried out in methanol