3643
J . Org. Chem. 1994,59, 3543-3546
Oxidative Halo-Decarboxylation of @-Unsaturated Carboxylic Acids Anette Graven, Karl Anker J~rgensen,'Staren Dahl, and Andrzej Stanczakl Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C, Denmark Received J a n w r y 20, 1994"
A procedure for oxidative halo-decarboxylation of a,,!?-unsaturatedcarboxylic acids using iodosylbenzene, or iodosylbenzene diacetate, and N-chloro-,N-bromo-, or N-iodosuccinimide is presented. Good yields of the corresponding bromoalkenes are obtained when the a,,!?-unsaturatedcarboxylic acids are substituted with an aromatic substituent in the ,!?-positionandN-bromosuccinimideis used as the halogenation reagent. The scope of mainly the oxidative bromo-decarboxylation reaction is presented, and a tentative mechanism is proposed.
Introduction The decarboxylation of organic carboxylic acids accompanied by a simultaneous replacement by a halogen under radical conditions is an extremely useful and selective reaction in organic chemistry for the synthesis of halogenated organic substances. The original method for oxidative halo-decarboxylation,known as the Hunsdiecker reaction, is the reaction of a silver salt of carboxylic acid with mainly bromine as the halogen? This procedure has been further developed, and today different methods are available for the oxidative halo-decarboxylation of organic carboxylic acids.3 The latter methods are known as the modified-Hunsdiecker reaction and probably also involve radical intermediates as radical initiators or photochemical reaction conditions are r e q ~ i r e d .Many ~ functional groups may be present in the Hunsdiecker and modified-Hunsdiecker reactions, but if the substrate is an a,@-unsaturatedcarboxylic acid, the reaction seldom gives good result^;^^^^ the Hunsdiecker bromo-decarboxylation of both trans- and &-cinnamic acid gives a yield of less than 15% of ,!?-bromostyrene.2b This paper presents a new synthetic procedure for oxidative bromo-decarboxylation of a,,!?-unsaturatedcarboxylic acids under nonradical conditions by which a bromine atom replaces the carboxylic acid substituent, using iodosylbenzene (IB),S or iodosylbenzene diacetate (IBDA),Sand N-bromosuccinimide (NBS).6 The replaceAbstract published in Advance ACS Abstracts, June 1, 1994. (1)On leave from the Institute of Drug Technology and Pharmaceutical Chemistry, MedicalAcademy, ul. Muezynskiego1,90-151Lodz, Poland. (2)(a)Wilson, C. V. Org. Reaet. (N.Y.) 1967,9,332. (b) Johnson, R. G.; Ingham, R. K Chem. Rev. 1956,66,219. (3)(a)McKillop, A; Bromley, D.; Taylor, E. C. J. Org. Chem. 1969, 34,1172.(b) Cambie, R. C.; Hayward, R. C.; Jurlina, J. L.; Rutledge, P. S.; Woodgate, P. D. J. Chem. Soc., Perkin Trans. 1 1981,2608.(c) Kochi, J. K. J. Am. Chem. Soc. 1966,87,2500.(d) Kochi, J.K J. Org. (e)Becker, K B.; Geisel,M.; Grob, C. A.; Kuhnen, Chem. 1965,30,3266. F. Synthesis 1973,493.(0Jenkins, C.L.; Kochi, J. K. J. Org. Chem. 1971,36,3095,3103. (g) Barton, D. H. R.; Crich, D.; Motherwell, W. L. Tetrahedron Lett. 1983,24,4979.(h)Barton, D. H. R.; Lacher, B.; Zard, S. Z. Tetrahedron 1987,43,4321. (i)Stofer, E.;Lion, C . Bull. Soc. Chim. Belg. 1987,96,623.(i)Hasebe, M.;Tsuchiya, T. Tetrahedron Lett. 1988,29,6287.(k) Patrick, T. B.; J O E ,K K; White, D. H.; Bertrand, W. S.; Mokhtar, R.; Kilbourn, M. R.; Welch, M. J. Can. J. Chem. 1986,64,138. (1) Grakauskas, V.J. Org. Chem. 1969,34,2446. (m) Concepcibn, J.I.;Francisco,C. G.; Freire, R.; Hernhdez, R.; Salazar, J. A.; Subez, E. J. Org. Chem. 1986,51,402. (4)March, J.Advanced Organic Chemistry, 4th ed.;John Wiley and Sons: New York, 1992;p 730. ( 5 ) For reviews about the chemistry of hypervalent iodosyl comSynthesis 1984, pounds: Varvoglis, A. Chem. Soc. Rev. 1981,10,377; 709. @
ment of the carboxylic acid substituent by chlorine and iodine atoms is also presented. The usefulness of the method will be presented for different substrates and an attempt to explain the mechanism of the reaction is made.
Results and Discussion a&Unsaturated carboxylic acids (1)undergo an oxidative bromo-decarboxylation by reaction with IB or IBDA and NBS (eq 1). Reaction oftruns-cinnamic acid (la)(1.0 R'
COOH
R2
R3
Y
NBS
*
(11
PhlO or Phl(0Ach
1
2
mmo1)with l.OmmolofNBSand0.5mmolofIB,orIBDA, in CH3CN/H20at 60 "C for 0.5 h affords ,!?-bromostyrene in 73% yield. The results of the oxidative bromodecarboxylation of a series of a,,!?-unsaturatedcarboxylic acids (1)using IB and NBS are presented in Table 1(for details see Experimental Section). The results in Table 1 show that 1 having an aromatic substituent in the ,!?-positionare the best substrates for the oxidative bromo-decarboxylation. It is seen that substrates having an aromatic substituent in the@position containing electron-donating groups (entries 2,4;lb,d) give a higher yield of the bromoalkene (2b,d)compared with one having an electron-withdrawing substituent (entry 3; IC). The stereochemistry at the double bond is to a high extent retained during the reaction, as transa,,!?-unsaturated carboxylic acids (la-d) mainly yield trans-bromoalkenes (entries 1-4; 2a-d), while a &+a,,!?unsaturated carboxylic acid (le) produces mainly the corresponding cis-bromo compound (entry 5;2e). For the bromo-decarboxylation it is found that the introduction of a substituent at the a carbon leads to a decrease of the yield of the correspondingbromoalkene and that the yield decreases as the sizdelectron-donating properties of the substituent at the a carbon increase (entries 6,7;lf,g). The method is also efficient for substrates having both an aryl- and an aryValky1substituent at the ,!? carbon (entries 8,9;lh,i),whereas substrates with an alkyl substituent only at the ,!? carbon are not very reactive in the present (6)For a review about reactionofNBSwith unsaturated acids: Pizey, J. S. Synthetic Reactions; Ellis Howard Ltd: Chister, 1974;Vol. 2,p 1.
0022-326319411959-3543$04.50/00 1994 American Chemical Society
3544 J. Org. Chem., Vol. 59, No. 13, 1994
Graven et al.
Table 1. Results for the Oxidative Bromo-Decarboxylation of a&Unsaturated Adds (1) Using Iodoeylbenzene and NBS 2
entrv comDd
R1
yield (96) (t:cP . .
R3
R2
1
la
H
Cas
H
2
lb
H
p-CHsOC&
H
3
IC
H
p-ClC&
H
4
Id
H
p-CHaC&
H
5
l
H
O-C&OC&
6
lf
7
lg
Cas H Cas p-ClC& Cas
H CSHS CH3 m,p-(C&0)2CsH~ H
8 9 10
lh li
II
e
H CH3 CeHs H H H
73 (96:6) 67b (1000) 51b (96:4) 65b (1000) 6ob (12:88) 3%
