OLEFINICPOSITIONIN UNSATURATED hcr~s
M a y 5 , 1954 [CONTRIBUTION F R O M
THE
DEPARTMENT O F CHEMISTRY O F
THE
2315
UNIVERSITY OF WISCONSIN]
Assignment of the Olefinic Position in Unsaturated Acids by Means of the Iodolactonization Reaction B Y EUGENE E.
VAN
TAXELEN AND MAURICE SHAMMA
RECEIVED NOVEMBER 27, 1953
Bv means of infrared spectrophotometric methods certain P,r- and y,&unsaturated acids have been shown to yield fivemembered iodolactones on treatment with iodine-potassium iodide in bicarbonate solution a t room temperature. The single 6,e-unsaturated acid studied, 6,e-hexenoic acid, yields (probably) 6-iodomethyl-6-valerolacto1ie, whereas acids with double bonds farther removed from the carboxyl function lead to unstable, poorly-defined products.
I n an endeavor to locate the position of a double bond relative to a carboxyl group in a certain sesquiterpenoid, we have applied to advantage the reaction in which certain unsaturated acids are converted by iodine-potassium iodide and bicarbonate in aqueous medium to iodolactones. The possibility that others may be faced with similar structural problems prompts us to detail the results obtained in a study of this readily executed reaction. Iodolactonization was first reported in 1908 by Bougault, whose fairly comprehensive report may be summarized by stating that (i) a,@-unsaturated acids do not give iodolactones, (ii) Ply- as well as y,&unsaturated acids do afford iodolactones, (iii) b,c-acids or acids with the unsaturation farther removed from the carboxyl group yield only the poorly characterized unsaturated acid iodohydrins, and (iv) a-keto-@,y-alkenoic acids and a,@-y,Gacids are exceptional in that no iodolactones are obtained from them. Bougault surmised correctly that the @,y-acids lead to @-iodo-y-lactones(1), but incorrectly-as we shall demonstrate later-that the y,d-isomers result in y-iodo-&lactones (11). The cyclization method has been utilized more reI\--,
/ \
IZ~O/'O I
I\A
I ' R/'o\o
revealing the five-membered nature of the lactone rings. CHjCH=CI-ICHI-COOH I11
+I (K
= -CH
>
0
A
A/ \
IL'
V
It is readily apparent that for lactones derived from y,b-unsaturated acids there are two structural possibilities : 6-iodo-y-lactones (e.g., VI) and yiodo-&lactones, the latter being favored, as mentioned above, by Bougault. Infrared analysis (Ta-
VI ble I) indicated that both y,b-pentenoic acid (VII) and A2-cyclohexeneaceticacid (VIII) gave rise to the y-lactones VI and IX, rather than the 6-isomers. The latter type would be expected, like CHz=CHCHzCHzCOOH VI1
+V I
I1
cently by Linstead2 and others3 to distinguish a,/% unsaturated acids from the @,y-isomers. Arnold4 has shown that iodolactones can be obtained by the use of cyanogen iodide in place of iodine and bicarbonate. Our first aim was extension of the series of lactones derived from 0, y-acids as well as confirmation of the lactone ring size. Toward this end, Plybutenoic acid, @,y-pentenoicacid (111) and A'-cyclohexeneacetic acid (IV) were treated with the iodine-bicarbonate reagent. Surprisingly enough, @, y-butenoic acid (an example not previously reported)? even on long standing, deposited n o iodolactone. The other two acids rapidly afforded iodolactones, which, like the subsequent members in this study, were analyzed by iodine determination. Both iodolactones exhibited strong absorption in the 5.6 region5b6of the infrared (Table I), thereby (1) 5. Bougault, A n n . chim. p h y s . , 14, 145 (1908); 15, 296 (1908). (2) R. P. Linstead and C. J. May, J. Chem. Soc., 2565 (1927). (3) (a) A. W. Schrecker, G . Y .Greenberg and J. L. Hartwell, THIS J O U R N A L , 74, 5669 (1952); (b) A. W. Schrecker and J. L. Hartwell, ibid., 1 4 , 5676 (1952). (4) R. T.Arnold and I(.I,. Lindsay, i b i d . , 76, 1048 (1953). (5) R. S. Rasrnussen and I
