ORGANIC
LETTERS
1999
Vol. 1, No. 8
1299-1301
Smooth Synthesis of Aryl- and
Alkylanilines by Photoheterolysis of
Haloanilines in the Presence of
Aromatics and Alkenes
Maurizio Fagnoni, Mariella Mella, and Angelo Albini*
Department of Organic Chemistry, UniVersity of PaVia, Via Taramelli 10,
27100 PaVia, Italy
Received August 24, 1999
ABSTRACT
Irradiation of 4-chloro-N,N-dimethylaniline in acetonitrile in the presence of benzene and of various alkenes leads to heterolytic dehalogenation
and trapping of the cation. 4-(Dimethylamino)biphenyl is formed in the first case, while with alkenes â-chloroalkylanilines, stilbenes, or allylanilines
are obtained depending on the alkene structure. 4-Fluoroaniline is similarly dehalogenated.
Phenyl cations have been the subject of active research from
the mechanistic point of view.1 These are usually generated
under proper conditions from diazonium salts2 and have been
spectroscopically characterized both in matrix3 and in the
gas phase.4 In the few case where the products from the
reaction in solution have been characterized, both reduction
and addition to O- and N-centered nucleophiles have been
found to occur.2a,5 On the contrary, C-C bond formation
does not involve the cation. When biaryls are formed from
diazonium salts, as in the Gomberg-Bachmann or in the
Pschorr reactions,6 the actual reacting species is the aryl
radical. Recently, however, Steenken and McClelland7
reported the formation of biphenyls by irradiation of phenyl-
diazonium salts in the presence of benzene derivatives and
showed that the process involved the cation.
We are pleased to report in the following an alternative
generation of aryl cations and to show that this gives rise to
synthetically useful reactions.
(1) (a) Rappaport, Z., Stang, P. J., Eds. Dicordinate Carbocations;
Wiley: New York, 1997. (b) Zollinger, H. Angew. Chem., Int. Ed. Eng.
1978, 17, 141.
Irradiation of both 4-chloro- and 4-fluoro-N,N-dimethyl-
aniline (1a,b) in acetonitrile caused reductive dehalogenation
to 2, but important products were also the corresponding 2,4′-
bis(N,N-dimethylamino)biphenyls 3 (ca. 30%, see Scheme
1). This appeared a clear indication that a phenyl cation was
formed under this condition.
(2) (a) Gasper, S. M.; Devadoss, C.; Shuster, G. B. J. Am. Chem. Soc.
1995, 117, 5206. (b) Swain, C. G.; Sheats, J. E.; Harbison, K. G. J. Am.
Chem. Soc. 1975, 97, 783. (c) Bergstrom, R. G.; Landells, R. G. M.; Wahl,
G. W.; Zollinger, H. J. Am. Chem. Soc. 1976, 98, 3301. (d) Speranza, M.;
Keheyan, Y.; Angelini, G. J. Am. Chem. Soc. 1983, 105, 6377.
(3) (a) Ambroz, H. B.; Kemp, T. J. J. Chem. Soc., Perkin Trans. 2 1980,
768. (b) Ambroz, H. B.; Kemp, T. J.; Prybytniak, G. K. J. Photochem.
Photobiol. A 1997, 108, 149. (c) Chauduri, A.; Loughlin, J. A.; Romsted,
L. S.; Yao, J. J. Am. Chem. Soc. 1993, 23, 269.
(4) (a) Speranza, M. Chem. ReV. 1993, 93, 2933. (b) Hrusa´k, J.; Schro¨der,
D.; Iwata, S. J. Am. Chem. Soc. 1993, 115, 2015. (c) Filippi, A.; Lilla, G.;
Occhiucci, G.; Sparapani, C.; Ursini, O.; Speranza, M. J. Org. Chem. 1995,
60, 1250.
(5) Romsted, L. S.; Zhang, J.; Zhuang, L. J. Am. Chem. Soc. 1998, 120,
10046.
(6) Hey, D. H. In AdVnces in Free radical Chemistry; Williams, G. H.,
Ed.; Academic Press: New York, 1980; Vol. 2, p 47. (b) Kametani, K.;
Fukumoto, K. J. Heterocycl. Chem. 1971, 8, 341.
(7) Steenken, S.; Askokkuna, M.; Maruthamuthu, P.; McClelland, R. A.
J. Am. Chem. Soc. 1998, 120, 11925.
10.1021/ol990982g CCC: $18.00 © 1999 American Chemical Society
Published on Web 09/23/1999