17 Succinimidyl and Related Radicals PHILIP S. SKELL and JAMES C. DAY
Downloaded by CORNELL UNIV on August 29, 2016 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0069.ch017
Department of Chemistry, The Pennsylvania State University, University Park, PA 16802
The chemical p r o p e r t i e s of s u c c i n i m i d y l r a d i c a l s remained a mystery u n t i l the simultaneous r e c o g n i t i o n i n the l a b o r a t o r i e s of Professor J . G. Traynham (1) and ours (2) that the r a d i c a l could be a chain c a r r i e r i n the sense first suggested by Bloomfield ( 3 ) , a l b e i t i n c o r r e c t l y (4), f o r the allylic bromination r e a c t i o n . For substrates which r e a c t r e a d i l y with bromine atoms, s u c c i n i m i d y l mediated brominations a r e c a r r i e d out in the presence of bromine scavengers (ethylene or t - b u t y l e t h y l e n e ) , employing a good solvent f o r NBS such as methylene c h l o r i d e . In these circumstances bromination occurs with a selectivity which c l o s e l y resembles Cl· mediated c h l o r i n a t i o n s .
Additions to alkenes and arenes a l s o occur r e a d i l y .
In all of these r e a c t i o n s the selectivities a r e remarkable f o r r a d i c a l r e a c t i o n s , being c h a r a c t e r i s t i c of n o - s t a b i l i z a t i o n of t r a n s i t i o n s t a t e s by c o n t r i b u t i o n s from product s t r u c t u r e s . Each of these r e a c t i o n s appears to be an encounter-controlled r e a c t i o n . As an illustration, s u c c i n i m i d y l r a d i c a l adds to styrene as f o l l o w s : to the double bond twice as r a p i d l y as to the phenyl nucleus.
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Pryor; Organic Free Radicals ACS Symposium Series; American Chemical Society: Washington, DC, 1978.
17.
SKELL AND DAY
Succinimidyl
and
Related
Radicals
291
Downloaded by CORNELL UNIV on August 29, 2016 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0069.ch017
With s u b s t r a t e s which do not react with bromine atoms, a mixture of Br2 and NBS i s e f f e c t i v e i n bromination, s u c c i n i m i d y l a b s t r a c t i n g the Η-atom, the product r a d i c a l r e a c t i n g with B ^ , and the Br* r e a c t i n g with NBS to regenerate the s u c c i n i m i d y l radical. These two methods f o r generating s u c c i n i m i d y l r a d i c a l s ( i n the presence of o l e f i n s or bomine) produce d i f f e r e n t s u c c i n i m i d y l r a d i c a l s , ground s t a t e (π) i n the presence of Br2 and e x c i t e d s t a t e (OJJ) i n the presence of o l e f i n s (the evidence i s described elsewhere).
The r i n g opening r e a c t i o n , NBS -> β-bromopropionyl isocyanate, i s a r e a c t i o n of σ, but not π. F i n a n c i a l support came from the A i r Force O f f i c e of S c i e n t i f i c Research (2748C). Literature Cited (1) Traynham, J. G., and Lee, Y. S., J. Am. Chem. Soc., 96, 3590 (1974). (2) Day, J. C., Lindstrom, M. J . , and S k e l l , P. S., ibid., 96, 5616 (1974). (3) B l o o m f i e l d , G. F., J. Chem. Soc., 114 (1944). (4) Adam, J . , G o s s e l a i n , P. Α., and G o l d f i n g e r , P., Nature, 171, 704 (1953); G o s s e l a i n , P. Α., Adam, J . , and G o l d f i n g e r , P., B u l l . Soc. Chem. Belg., 65, 533 (1956); Sixma, F. L. J . , and Riem, R. Η., K. Ned. Akad. Wet. Proc., 61B, 183 (1958); McGrath, B. P., and Tedder, J . Μ., Proc. Chem. Soc., 80, (1961); Pearson, R. E. and M a r t i n , J. C., J. Am. Chem. Soc., 85, 354, 3142 (1963); W a l l i n g , C., Rieger, A. L., and Tanner, D. D., ibid., 85, 3129 (1963); R u s s e l l , G. Α., Do Boer, C., and Desmond, Κ. Μ., ibid., 85, 365, 3139 (1963); Incremona, J . H. and M a r t i n , J. C., ibid., 92, 627 (1970). RECEIVED
December 23, 1977.
Pryor; Organic Free Radicals ACS Symposium Series; American Chemical Society: Washington, DC, 1978.
