Zinc(II) promoted conversion of aryltriazenes to aryl iodides and aryl nitriles

Article abstract of DOI:10.1016/S0040-4039(01)00526-3

Aryltriazenes react with zinc perchlorate/zinc cyanide to produces arylnitriles and react with zinc iodide to produce aryliodides. The reaction mechanism involves aryl radicals that have been trapped by addition to propenenitriles in a good preparative Meerwein arylation process.

Full text of DOI:10.1016/S0040-4039(01)00526-3

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 3553–3554
Zinc(II) promoted conversion of aryltriazenes to aryl iodides
and aryl nitriles
Timothy B. Patrick,* Thomas Juehne, Elmer Reeb and Daniel Hennessy
Chemistry Department, Southern Illinois University, Edwardsville, IL 62026, USA
Received 1 March 2001; revised 27 March 2001; accepted 28 March 2001
Abstract—Aryltriazenes react with zinc perchlorate/zinc cyanide to produces arylnitriles and react with zinc iodide to produce
aryliodides. The reaction mechanism involves aryl radicals that have been trapped by addition to propenenitriles in a good
preparative Meerwein arylation process. © 2001 Elsevier Science Ltd. All rights reserved.
a
Table 1. Conversion of aryltriazenesb to arylnitrilesc and
Aryltriazenes, 1-aryl-3,3-dialkyltriazenes, have a long
aryliodidesc
history in both biological and chemical sciences.1,2 In
chemistry, the aryltriazenes function as synthetic inter-
mediates for the performance of aryldiazonium ion type
reactions in non-aqueous media. The triazene function
can be replaced by halogens, especially iodine, and by
many other groups found in aqueous diazonium ion
reactions.3–8 Following our studies reported in 1985 for
replacement of the triazene function with a phenyl ring,
we attempted without success to introduce a fluorine
group.1 In the course of these studies we conducted
reactions between aryltriazines and zinc salts. We
observed that the triazine function can be replaced by a
cyano group through the use of zinc cyanide/zinc per-
chlorate and can be replaced by iodine through the use
of zinc iodide. Our results provide some useful synthetic
methodology as well as interesting mechanistic consid-
erations and are the subject of this letter.
R
% CN
% I
H
4-CH3
4-Et
2-NO2
3-NO2
4-NO2
4-n-Bu
4-OEt
4-Cl
73
62
32
98
62
54
55
45
80
75
59
60
70
41
49
48
70
77
57
37
4-Br
a Products were identified by comparison of physical properties with
known physical properties.
b Aryltriazenes were obtained from the aromatic amines as described
in Ref. 1.
c Yields of isolated products.
Aryltriazenes, 1-aryl-3,3-(pentanediyl)triazenes (1),
reacted with a mixture of zinc perchlorate (1 equiv.)
and zinc cyanide (1 equiv.) in acetonitrile at reflux for 3
h to give arylnitriles (2) (Eq. (1)). The yields of purified
products are shown in Table 1.
temperature over a period of 2 hours (Eq. (2)). The
aryliodides (3) were easily isolated after filtration, evap-
oration and distillation. The yields are reported in
Table 1.
(1)
(2)
The reaction of aryltriazenes (1) with zinc iodide (3
equiv.) in acetonitrile solution occurred readily at room
The reaction of 1 with zinc iodide (1 equiv.) was
conducted in the presence of excess propenenitriles
* Corresponding author. E-mail: tpatric@siue.edu
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00526-3

3554
T. B. Patrick et al. / Tetrahedron Letters 42 (2001) 3553–3554
(3)
Scheme 1.
(4a–c). Meerwein-type9 arylation adducts 5a–c10 were
obtained in good yield (Eq. (3)). The observance of the
iodinated adducts provides evidence for the presence of
an aryl radical as an intermediate in these reactions.
The relative reactivity of propenenitrile (1), 2-methyl-
propenenitrile (2.7) and 2-butenenitrile (0.22) are also
consistent with an aryl radical addition reaction.11
2. Gross, M. L.; Blank, D. H.; Welch, W. M. J. Org. Chem.
1993, 58, 2104 and references cited therein.
3. Wu, Z.; Moore, J. S. Tetrahedron Lett. 1994, 35, 5539
and references cited therein.
4. Moore, J. S.; Weinstein, E. J.; Wu, Z. Tetrahedron Lett.
1991, 32, 2465.
5. Heindel, N. D.; Dort, M. V. J. Org. Chem. 1985, 50,
1988.
The mechanism outlined in Scheme 1 accounts for the
Meerwein arylation reaction that produces 5a–c. The
aryltriazene produces an aryl free radical (A) on reac-
tion with ZnI2. The radical adds in 1,4-addition to
produce the alkyl radical (B) that abstracts an iodine
atom from ZnI2. Our earlier work on triazene chemistry
showed that diazonium salts are primary intermediates
that decompose likely through aryl radicals.12 This
work lends further evidence to the involvement of aryl
radicals and further demonstrates the value of aryltri-
azenes as non-aqueous synthetic equivalents of aryl
diazonium ions.
6. Goodman, F. F.; Knapp, Jr., F. F.; Elmaleh, D. R.;
Strauss, H. W. J. Org. Chem. 1984, 49, 2322.
7. Satyamurthy, N.; Barrio, J. R. J. Org. Chem. 1983, 48,
4395.
8. Satymurthy, N.; Barrio, J. R.; Schmidt, D. G.; Kam-
merer, C.; Bida, G. T.; Phelps, M. E. J. Org. Chem. 1990,
55, 4560.
9. Rondestvedt, Jr., C. S. Org. React. 1976, 24, 225.
10. 5a: 1H NMR (CDCl3, TMS) l 3.25 (1H, d, J=5 Hz,
CH2), 4.23 (2H, t, J=5 Hz, CH), 7.2–7.4 (5H, aro-
matic); 5b: l 2.2 (3H, s, CH3), 3.25 (1H, d, J=3 Hz,
CH), 3.46 (1H, d, J=3 Hz, CH), 7.1–7.7 (5H, aro-
matic); 5c: l 1.6 (3H, d, J=6 Hz, CH3), 3.1 (1H, d of
m, 3–H), 5.31 (1H, m, 2-H), 7.4–7.5 (5H, aromatic). All
compounds gave satisfactory elemental analysis and
mass spectral data.
Acknowledgements
11. Competitive rates were determined from the reaction of
1 with zinc iodide (1 equiv.) in acetonitrile solution
with a 10-fold excess of propenenitrile and a 10-fold
excess of a competing nitrile. The ratios of products
were determined from integration of the peaks in the
1H NMR spectra of the mixtures.
12. Wassenmundt, F. W.; Kiesman, W. F. J. Org. Chem.
1997, 62, 8304 provide evidence for the formation of aryl
radicals from diazonium salts.
This work was supported by grants from the National
Science Foundation (RUI) and from the Petroleum
Research Fund-Type B.
References
1. Patrick, T. B.; Willaredt, R. P.; DeGonia, D. J. J. Org.
Chem. 1985, 50, 2232 and references cited therein.
.
.