ORGANIC LETTERS
Photostimulated Reactions of Phenylacetic Acid Dianions with Aryl Halides. Influence of the Metallic Cation on the Regiochemistry of Arylation
2000 Vol. 2, No. 17 2643-2646
Godson C. Nwokogu,† Jim-Wah Wong, Thomas D. Greenwood, and James F. Wolfe* Department of Chemistry and the HarVey W. Peters Research Center for the Study of Parkinson’s Disease and Disorders of the Central NerVous System, Virginia Polytechnic Institute and State UniVersity, Blacksburg, Virginia 24061
[email protected] Received June 8, 2000
ABSTRACT
Phenylacetic acid dianions react via what appears to be an SRN1 process with aryl halides under photostimulation to afford aryl substitution products 5 and 6. When the counterion is K+, only 4-biphenylacetic acids 5 are obtained. Both r- and para-coupling occurs with Na+ to give a mixture of 5 and 6, while exclusive formation of diphenylacetic acids 6 is observed with the dilithio salt of 1.
As part of a continuing study of radical-chain nucleophilic aromatic substitution reactions, we had discovered previously that photoinduced reactions of aryl and hetaryl halides with phenyl-stabilized carbanions such as the potassium enolate of ethyl phenylacetate (1a)1,2 and potassiophenylacetonitrile (1b)3-5 proceed by the radical-chain SRN16 mechanism to form mainly products 2a,b, derived from coupling of aryl †
Hampton University, Department of Chemistry, Hampton, VA 23668. (1) Wong, J.-W.; Natalie, K. J.; Nwokogu, G. C.; Pisipati, J. S.; Flaherty, P. T.; Greenwood, T. D.; Wolfe, J. F. J. Org. Chem. 1997, 62, 61526159. (2) Wong, J.-W. Ph.D. Dissertation, Virginia Polytechnic Institute and State University, 1981. (3) Hermann, C. K. F.; Sachdeva, Y. P.; Wolfe, J. F. J. Heterocycl. Chem. 1984, 24, 1061-1065. (4) Hermann, C. K. F. Ph.D. Dissertation, Virginia Polytechnic Institute and State University, 1984. (5) Bunnett, J. F.; Gloor, B. F. J. Org. Chem. 1973, 38, 4156-4163. (6) For reviews, see: (a) Rossi, R. A.; de Rossi, R. H. Aromatic Substitution by the SRN1 Mechanism; ACS Monograph 178; American Chemical Society: Washington, DC, 1983. (b) Norris, R. K. Compr. Org. Synth. 1991, 4, 451-482. (c) Rossi, R. A.; Pierini, A. B.; Santiago, A. N. Org. React. 1999, 54, 1-271. 10.1021/ol006177f CCC: $19.00 Published on Web 07/26/2000
© 2000 American Chemical Society
radicals at the R-position (Scheme 1). However, while ester enolate 1a reacted to give only R-substituted product 2a, potassionitrile 1b afforded small amounts (
