Reactions of SmI2 with Nitro Olefins

Full text of DOI:10.1021/jo961608m

J . Org. Chem. 1997, 62, 771-772
771
2
Rea ction s of Sm I w ith Nitr o Olefin s
Avihai Yacovan and Shmaryahu Hoz*
Department of Chemistry, Bar-Ilan University,
Ramat Gan, Israel 52900
Received August 19, 1996
SmI
2
, one of the most versatile single electron transfer
1
reducing agents, is capable of reducing nitro compounds
2
3,4
to the corresponding hydroxylamines, amines, and azo
derivatives.3 In the absence of a proton source, the
reduction results in the formation of azo- and azoxyben-
zene. When SmI
dinitroethylene (DPDN) in THF at room temperature for
min prior to quenching with 10% aqueous HCl, the
2
was reacted with 1,1-diphenyl-2,2-
2
products shown in eq 1 were obtained. Dry air quenching
according to the procedure of ref 1h gave identical results.
F igu r e 1. Product distribution in the reaction of SmI
DPDN as a function of SmI
; 1, 3.
2
with
2
equivalents: b, DPDN; 9, 1; 2,
Table 1 shows an interesting connection between the
2
number of equivalents of SmI
various products.
2
used and the yield of the
Ta ble 1. P r od u ct Distr ibu tion a s a F u n ction of th e
Nu m ber of Sm I2 Equ iva len ts Used in Its Rea ction w ith
DP DN
This data, plotted in Figure 1, shows that the initial
consumption of the starting material is relatively low and
increases significantly above 6 equiv of SmI . This can
2
no. of SmI2 (equiv)
DPDN
1
2
3
be taken as an indication that (a) the production of the
first irreversibly formed intermediate is a relatively slow
2
4
6
8
89
0.7
1
1.2
4.6
14.8
10.3
20.2
25.8
43.4
59.4
0
2
4.3
8
4.3
76.8
68.7
44
(
not a diffusion-controlled) process and (b) the intermedi-
ates further down the cascade react much faster with
SmI than does the substrate. The monomeric product,
diphenylacetonitrile (1), is formed in substantial amounts
>10%) only above 8 equiv of SmI . When 14 equiv of
SmI was used and the reaction was quenched after 2 h,
1
0
21.5
2
7
the CdC(CN)
2
and the CdO groups, 1,1-diphenyl-2,2-
(
2
dicyanoethylene does not yield any dimeric products.
Instead, it is quantitatively reduced by 2 equiv of SmI
2
2
1
was obtained as the sole product in a quantitative yield.
It is possible that diphenylacetonitrile is obtained as
eq 2).8
(
a result of a reductive cleavage of the dimer, tetraphe-
nylsuccinonitrile 2. To test this possibility, the latter
5
compound was independently synthesized and was al-
lowed to react with 2 equiv of SmI
2
. Quenching with a
The coupling process is even more surprising when
1
0% aqueous HCl solution after 2 min yielded 25% of
contrasted with the reaction of DPDN with sodium
naphthalenide in THF. When a solution of 0.014 M
DPDN in THF was allowed to react with 2.5 equivof
sodium naphthalenide, an entirely different type of
dimerization was obtained (eq 3).
diphenylacetonitrile. Thus, it is possible that tetraphe-
nylsuccinonitrile is formed first and reacts further with
SmI
2
to give diphenylacetonitrile. Nevertheless, the
reacts with an inter-
possibility that the excess of SmI
2
mediate, which otherwise would have coupled to give the
dimer, can not be discarded.
The dimerization to give 2 is similar to the reaction of
SmI
tion (along with benzhydrol).
however, that in spite of the noted similarity between
2
with benzophenone, which results in pinacol forma-
3
,6
It is interesting to note,
(
1) (a) Namy, J . L.; Girard, P.; Kagan, H. S. New J . Chem. 1977, 1,
5
. (b) Molander, G. A. Chem. Rev. 1992, 92, 26. (c) Molander, G. A. In
Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Per-
gamon: Oxford, 1991; Vol. 4. (d) Soderquist, J . A. Aldrichim. Acta 1991,
2
4, 15. (e) Kagan, H. B. New J . Chem. 1990, 14, 453. (f) Kagan, H. B.;
Most likely, the trivalent Sm produced plays an
important role in determining the course of the reaction.
Finally, 1,1-diphenyl-2-nitro-2-bromoethylene (DPNBr)
Sasaki, M.; Collin, J . Pure Appl. Chem. 1988, 60, 1725. (g) Kagan, H.
B.; Namy, J . L. Tetrahedron 1986, 42, 6573. (h) Hasegawa, E.; Curran,
D. P. J . Org. Chem. 1993, 58, 5008 and references cited therein.
(
(
2) Kende, A. S.; Mendoza, J . S. Tetrahedron Let. 1991, 32, 1699.
3) Souppe, J .; Danon, L.; Namy, J . L.; Kagan, H. B. J . Organomet.
2
reacts with SmI in a way similar to DPDN (eq 4).
Chem. 1983, 250, 227.
(
(
(
4) Zhang, Y.; Lin, R. Synth. Commun. 1987, 17, 329.
5) Kharasch, M. S.; Sosnovsky, G. Tetrahedron 1958, 3, 97.
6) Namy, J . L.; Scouppe J .; Kagan, H. B. Tetrahedron Lett. 1983,
2
4, 765.
S0022-3263(96)01608-8 CCC: $14.00 © 1997 American Chemical Society

7
72 J . Org. Chem., Vol. 62, No. 3, 1997
Notes
Ta ble 2. P r od u ct Distr ibu tion a s a F u n ction of th e
Nu m ber of Sm I2 Equ iva len ts Used in Its Rea ction w ith
DP NBr
in the glovebox. The total reaction volume was 5 mL. After 2
min, the reaction mixture was quenched with excess 10% HCl
solution and extracted twice with dichloromethane. The organic
phase was dried over Na
Analyses were carried out by HPLC and NMR in acetone-d
2 4
SO , and the solvent evaporated.
no. of SmI2 (equiv)
DPNBr
4
1
2
3
6
.
2
4
8
57
26
8.1
2.3
12
10.1
3.7
6
40.6
37
49
36
0
7
5.2
The identity of the products, diphenylacetonitrile (1), tetraphen-
5
5
ylsuccinonitrile (2), and benzophenone (3), was established by
comparison with authentic samples.
2
Rea ction of Tetr a p h en ylsu ccin on itr ile w ith Sm I . The
reactions were performed and analyzed employing the same
procedure used for the reactions of DPDN. Quenching of the
reaction mixture after 2 min gave 25% of diphenylacetonitrile
However, this reaction differs from that of DPDN in
two aspects. First, the formation of the bromo product
in this reaction is not paralleled by formation of a nitro
vinyl system in the reaction of DPDN. Second, the
substrate consumption as a function of the number of
SmI equivalents used is enhanced more than twice
2
compared with that of the DPDN reaction (Table 2). It
is therefore not unreasonable to assume that, in the
(1). Quenching after 2 h yielded 70% of 1 (NMR yields).
Rea ction s of DP DN w ith Sod iu m Na p th a len id e. Sodium
naphthalenide was prepared in the following way. To a solution
of 4 g (0.031 mmol) of sublimed naphthalene in 50 mL of THF
was added 0.54 g (0.023 mmol) of clean sodium chips. The
reaction mixture was stirred for 1 day until the metal was
completely dissolved. The concentration of the sodium naph-
reaction of DPDN with SmI
2
, the leaving “nitro” group
-
thalenide was determined by titrating the OH produced by
undergoes at least a partial reduction (consuming this
pouring a measured sample of the solution into water.
way additional equivalents of SmI
from the molecule.
2
) before it is expelled
To a THF solution of DPDN (11.6 mg, 0.043 mmol) was
injected a measured volume of a 0.43 M solution of sodium
naphthalenide. The total volume of the reaction mixture was 3
mL. After 5 s, the reaction was quenched by excess trifluoro-
acetic acid and extracted twice with dichloromethane. The
Exp er im en ta l Section
NMR spectra were determined on a Bruker AM 300 spec-
trometer. Mass spectra were determined using a VG Autospec
instrument. UV spectra were recorded on a Kontron UVIKON
2 4
organic phase was dried over Na SO and evaporated. Product
distribution was determined by HPLC using 4% THF in heptane
as eluent. Two of the products are known compounds: ben-
zophenone (3) and 1,1-diphenyl-2-nitroethylene.11 The dimer
1,1,4,4-tetraphenyl-2,3-dinitrobutadiene was recrystallized from
8
10 spectrophotometer, and the HPLC analyses were performed
on a Waters machine equipped with an Alltech Econosil column.
9
1
Rea ction s of 1,1-Dip h en yl-2,2-d in itr oeth ylen e (DP DN)
a 1:1 mixture of hexane:ether: mp 260-262 °C; H NMR δ 6.88-
1
0
13
a n d 1,1-Dip h en yl-2-n itr oeth ylen e (DP NBr ) w ith Sm I
commercial (Aldrich) 0.1 M THF solution of SmI was used. The
exact concentration of the SmI was determined both by I
titration and by vis spectroscopy at 616 and 552 nm.
2
. A
7.02 (m, 4H), 7.23-7.35 (m, 6H); C NMR 138.29 s, 138.15 s,
2
130.52 d, 129.5 d, 130.29 d, 128.47 d, 128.56 d, 128.18 d, 152.54
s, 143.77 s; MS (EI) 448, 402, 356, 178. Satisfactory C,H,N
analyses were obtained.
2
2
In a typical reaction, 0.026 mmol of the substrate was weighed
into a 25 mL round-bottom flask that was sealed with a septum
and flushed with argon. The solid was dissolved in THF, and
Ack n ow led gm en t. This paper is dedicated to Prof.
Zvi Rappoport on the occasion of his 60th birthday. We
thank the Bar-Ilan Research Authority for supporting
the research and Dr. I Bilkis for helpful discussions.
2
an appropriate amount of the THF solution of SmI was added
(
(
(
7) Rappoport, Z. Isr. J . Chem. 1970, 8, 749.
8) Yacovan, A.; Hoz, S.; Bilkis, I. J . Am. Chem. Soc. 1996, 118, 261.
9) Hegarty, A. F.; Lomas, J . S.; Wright, W. V.; Bergmann, E. D. J .
J O961608M
Org. Chem. 1972, 37, 2222.
10) Allen, C. F. H.; Wilson, C. V. J . Org. Chem. 1940, 5, 146.
(
(11) Bordwell, F. G.; Gabrisch, E. W. J . Org. Chem. 1962, 27, 3049.