Wilkinson's catalyst catalyzed selective hydrogenation of olefin in the presence of an aromatic nitro function: A remarkable solvent effect

Article abstract of DOI:10.1021/jo025595q

Optimal conditions for chlorotris(triphenylphosphine)rhodium(I) (Wilkinson's catalyst) catalyzed selective saturation of a double bond in the presence of a nitro function are developed. Aryl iodide and benzyl ether are also tolerated under these hydrogenation conditions.

Full text of DOI:10.1021/jo025595q

J . Org. Chem. 2002, 67, 3163-3164
3163
Wilk in son ’s Ca ta lyst Ca ta lyzed Selective
Sch em e 1
Hyd r ogen a tion of Olefin in th e P r esen ce of
a n Ar om a tic Nitr o F u n ction : A
Rem a r k a ble Solven t Effect
†
Ang e´ lique J ourdant, Eduardo Gonz a´ lez-Zamora, and
J ieping Zhu*
Institut de Chimie des Substances Naturelles, CNRS,
Ta ble 1. Hyd r ogen a tion of Olefin (1a ) Ca ta lyzed by
Wilk in son ’s Ca ta lyst: A Su r vey of Rea ction Con d ition s
9
1198 Gif-sur-Yvette
entry
solvent
MeOH
pressure/time
yield of 2a (%)a
1
2
3
4
5
6
7
8
9
1 atm/48 h
1 atm/48 h
1 atm/48 h
3 bar/48 h
1 atm/48 h
1 atm/48 h
3 bar/48 h
1 atm/7 h
1 atm/5 h
1 atm/48 h
80
0
<20
<50
0
trace
<50
91
zhu@icsn.cnrs-gif.fr
b
C6H6
C6H5Mec
C6H5Me
Received February 6, 2002
d
MeOH/C6H6
MeOH/C6H5Med
MeOH/C6H5Me
THF
Abstr a ct: Optimal conditions for chlorotris(triphenylphos-
phine)rhodium(I) (Wilkinson’s catalyst) catalyzed selective
saturation of a double bond in the presence of a nitro
function are developed. Aryl iodide and benzyl ether are also
tolerated under these hydrogenation conditions.
t
BuOH-THFe
95
93
1
0
MeOH-THFe
a
Isolated yield. b Benzene. c Toluene. d v/v ) 2/1. e v/v ) 1/1.
tions has been documented.7 In connection with our
ongoing project, a process allowing selective saturation
of an olefin in the presence of an aromatic nitro group
was required (Scheme 1). Being unable to realize this
transformation with various in situ generated diimide
species,8 we turned our attention to the Wilkinson’s
catalyst and observed a remarkable solvent effect, which
constitutes the subject of the present note.
The nitro group is certainly one of the most reducible
functions in transition metal catalyzed hydrogenation
1
process. Therefore, selective saturation of an olefin in
the presence of an aromatic nitro group is a demanding
task and, indeed, very few general methods have been
described in the literature. While selective reduction of
a double bond in the presence of a nitro function with
In the hydrogenation of olefins catalyzed by Wilkin-
son’s catalyst, benzene, methanol, and a benzene-
methanol mixture were the most frequently used reaction
media. To our surprise, however, the hydrogenation of
a in benzene at 1 atm led only to the recovered starting
material after 48 h of stirring. Although selective satura-
tion of olefin did occur in methanol, the long reaction time
required (48 h) prompted us to investigate in detail the
solvent effect on this transformation. As shown in Table
2
3
4
Baker’s yeast and metal hydride have been reported,
their application seems to be limited to Michael acceptors.
For the reduction of an isolated double bond without
touching the nitro group, the diimide protocol5 and
hydrogenation catalyzed by homogeneous catalysts such
as chlorotris(triphenylphosphine)rhodium(I) (Wilkinson’s
9
1
6
catalyst) have been reported by a number of groups and
are well-recognized. However, to the best of our knowl-
edge, no systematic studies have been carried out to
determine the optimal conditions even with Wilkinson’s
catalyst and, indeed, reduction of aromatic nitro com-
pounds to aniline derivatives under hydrogenation condi-
1
, tetrahydrofuran (THF) turned out to be the solvent of
1
0
choice (entry 8). The addition of a protic cosolvent,
notably the tert-butyl alcohol, accelerated further the
reaction course (entry 9). Overall, under optimized condi-
tions (4% Wilkinson’s catalyst, 1/1 tert-BuOH-THF at
rt, 1 atm), olefin 1a was reduced within 5 h to provide
*
To whom correspondence should be addressed. Fax: +33 1 69 07
7
2 47.
†
Dr. E. Gonz a´ lez-Zamora is a visiting Professor from Universidad
Aut o´ noma Metropolitana-Iztapalapa, Av. Michoac a´ n y Pur ´ı sima Col.
Vicentina Iztapalapa, 09340 M e´ xico, D. F.
(7) For examples, see: (a) Love, C. J .; McQuillin, F. J . J . Chem. Soc.,
Perkin Trans. I 1973, 2509-2512. (b) Amer, I.; Bravdo, T.; Blum, J .;
Vollhardt, K. P. C. Tetrahedron Lett. 1987, 28, 1321-1322.
(1) Rylander, P. N. Catalytic Hydrogenation in Organic Syntheses;
Academic Press: New York, 1979; pp 114-137.
(
2) Takeshita, M.; Yoshida, S.; Kohno, Y. Heterocycles 1994, 37, 553-
(8) Following conditions allowing the in situ generation of diimide
5
62.
were examined: (a) NH
2 2 2 2 2
OH‚HCl, KOH; (b) PhIO(Ac) , NH NH ‚H O;
(3) (a) Aizpurua, J . M.; Oiarbide, M.; Palomo, C. Tetrahedron Lett.
(c) potassium azo dicarboxylate, AcOH.
1
987, 28, 5365-5366. (b) Gupta, A.; Haque, A.; Vankar, Y. D. J . Chem.
(9) (a) Birch, A. J .; Walker, K. A. M. J . Chem. Soc. C 1966, 1894-
1896. (b) Harmon, R. E.; Parsons, J . L.; Cooke, D. W.; Gupta, S. K.;
Schoolenberg, J . J . Org. Chem. 1969, 34, 3684-3685.
(10) Both THF and tert-butyl alcohol have been examined as
hydrogen-donating solvents in transfer hydrogenation of olefins cata-
lyzed by Wilkinson’s catalyst (at high temperature in a sealed tube);
see: Nishiguchi, T.; Tachi, K.; Fukuzumi, K. J . Org. Chem. 1975, 40,
237-240.
Soc., Chem. Commun. 1996, 1653-1654.
(
4) Barrett, A. G. M.; Graboski, G. G. Chem. Rev. 1986, 86, 751-
62.
5) Pasto, D. J .; Taylor, R. T. In Org. React.; Paquette, L. A., Ed.;
J ohn Wiley & Sons: New York, 1991; Vol. 40, pp 91-155.
6) (a) Birch, A. J .; Williamson, D. H. In Org. React; Dauben, W. G.,
7
(
(
Ed.; J ohn Wiley & Sons: New York, 1976; Vol. 24, pp 1-186. (b)
Burgess, K.; Van der Donk, W. A. In Encyclopedia of Reagents for
Organic Synthesis; Paquette, L. A., Ed.; Wiley: New York, 1995; Vol.
(11) (a) Biellmann, J . F.; J ung, M. J . J . Am. Chem. Soc. 1968, 90,
1673-1674. (b) Augustine, R. L.; Van Peppen, J . F. J . Chem. Soc.,
Chem. Commun. 1970, 495-496.
2
, pp 1253-1261.
1
0.1021/jo025595q CCC: $22.00 © 2002 American Chemical Society
Published on Web 04/11/2002

3
164 J . Org. Chem., Vol. 67, No. 9, 2002
Notes
Ta ble 2. Selective Hyd r ogen a tion : a Su bstr a te Su r vey
The reaction conditions thus developed were found to
be quite general and have been applied to the selective
reduction of various substrates such as nitro-substituted
cinnamates, allylic alcohols, styrenes, and stilbenes
(Table 2). The benzyl ether and even aryl iodide (1k ) were
tolerated under these mild hydrogenation conditions. The
yield was generally excellent except for the allyl azide
(1e). In this case, the conversion is low due to probably
the increased stability of the rhodium-olefin complex via
6
the participation of the azide function. As expected, it
was observed that the reduction of cis-olefin is faster than
the trans counterpart. Indeed, during the reduction of
geometrically pure cis-1k , partial isomerization of cis-
1
k to trans-1k was observed when the reaction medium
1
1
was not carefully degassed.
In conclusion, we developed general conditions allowing
selective hydrogenation of olefins in the presence of an
aromatic nitro function. In view of the widespread use
of the nitro group as an activating group and as a
surrogate of other functional groups, such a selective
reduction process should find applications in complex
organic synthesis.
Exp er im en ta l Section
Gen er a l P r oced u r e. To a solution of substrate 1 in degassed
solvent (1/1 THF/tert-butyl alcohol, 0.14 M) and saturated by
hydrogen was added 4% Wilkinson’s catalyst. The solution was
stirred under a hydrogen atmosphere at room temperature.
When the hydrogenation was deemed complete by TLC, the
reaction mixture was filtered through a short pad of alumina
and washed thoroughly with diethyl ether. Purification by flash
chromatography on silica gel provided the saturated nitro
aromatic alkane 2 in excellent yield (Table 2).
Ack n ow led gm en t . We thank CNRS for financial
support. A doctoral fellowship from the Minist e` re de
l’Enseignement Sup e´ rieur et de la Recherche to A.
J ourdant and a research fellowship from CONACYT,
M e´ xico, to E. Gonz a´ lez-Zamora are gratefully acknowl-
edged.
a
Isolated yield. b Recovered starting material accounted for the
Su p p or tin g In for m a tion Ava ila ble: Full characteriza-
tion data for compounds 2a -k . This material is available free
of charge via the Internet at http://pubs.acs.org.
mass balance.
the desired saturated nitro aromatic alkane 2a in 95%
yield.
J O025595Q