11964
J. Am. Chem. Soc. 1996, 118, 11964-11965
Allylic Amination of Cyclohexene Catalyzed by
Ruthenium Complexes. A New Reaction Involving
an Intermolecular C-H Functionalization
and the turnover numbers are higher than those reported for
most C-H activation reactions. Only one precedent exists for
7
an analogous reaction also examined in our laboratories, but
only trace amounts of allylic amine were obtained in that case,
8
the main products being ureas and anilines.
1
Sergio Cenini,* Fabio Ragaini, Stefano Tollari, and
The reduction of aromatic nitro compounds by CO catalyzed
by Ru3(CO)12 in the presence of DIAN-R, in commercial
Daniele Paone
Dipartimento di Chimica Inorganica
Metallorganica e Analitica and CNR Center
V. G. Venezian 21, I-20133 Milano, Italy
ReceiVed December 11, 1995
Transition-metal-mediated intermolecular activation and func-
tionalization of C-H bonds is a topic of high current interest.
From another perspective, the functionalization of a simple
olefin by an external amine is also a topic that has attracted
much interest. However, the direct intermolecular addition of
an amine to an unactivated olefin, either metal-mediated or not,
cyclohexene as solvent and at 160 °C and 40 bar, gives the
corresponding allylamine derivatives as the main products (eq
1, Table 1). By-products of the reaction are the anilines
2
has met with only very limited success. As far as allylic amines
are considered as products, most reported synthetic procedures
proceed Via a palladium or nickel allyl complex. However, the
synthesis of these intermediates usually requires the availability
of a prefunctionalized starting material, such as an allyl acetate.
A few methods have been reported in the literature, which afford
3
-6
an allylic amine by a C-H activation reaction.
Stoichio-
metric reactions have been performed employing sulfur or
selenium imino compounds (RNdXdNR; X ) S, Se), or
corresponding to the nitro compounds. With a substrate/catalyst
ratio of 50, only in the case of Ar ) 4-MeOC6H4 is a complete
conversion not achieved (entry 1). Moreover, in this case the
reaction shows a poor selectivity. In the other cases, a complete
conversion is also accompanied by a much better selectivity.
The selectivity increases with an increase in the electron-
withdrawing power of the substituent on the nitroarene (Table
3
molybdenum oxaziridines.4 A few catalytic processes have also
been reported employing PhIdNTs5 or PhNHOH as the
nitrogen-containing compound, but the turnover numbers are
quite low and the aminating reagents are not readily available.
In this paper, we report on a new synthetic way to produce
allylic amines, employing a simple unactivated olefin, cyclo-
hexene, and an aromatic nitro compound as the aminating
reagent, under reducing conditions (CO pressure). Although
the method requires the use of a high-pressure apparatus, the
reagents are bulk, cheap commercial products which do not need
to be purified (although a higher selectivity can be achieved by
purifying the olefin), the experimental operation is easy, the
selectivity is high (up to 81.9% under unoptimized conditions),
6
1
, entries 1-5) (Figure 1, Supporting Information).
The amount of aniline formed during the reaction is quite
9
insensitive to the nature of the substituents. This observation
may be explained by the high tendency of some intermediate
complex formed during the reaction to react with adventitious
moisture more rapidly than any further step of the catalytic
reaction. We have already shown that the Ru3(CO)12/DIAN-
Me system is one of the best catalysts for the reduction of
1
0
(
1) E-mail: Ragaini@mail.csmtbo.mi.cnr.it.
nitrobenzene to aniline by CO/H2O.
However, when we
(
2) (a) Roundhill, D. M. Chem. ReV. 1992, 92, 1-27 and references
employed cyclohexene purified by distillation over Na/ben-
zophenone ketyl under the conditions of entry 5 in Table 1, the
selectivity in aniline was slightly changed, although the selectiv-
ity in allylic amine increased to 81.9% (with a mass balance of
therein. (b) Casalnuovo, A. L.; Calabrese, J. C.; Milstein, D. J. J. Am. Chem.
Soc. 1988, 110, 6738-6744.
(
3) (a) Sharpless, K. B.; Hori, T. J. Org. Chem. 1976, 41, 176-177. (b)
Sharpless, K. B.; Hori, T.; Truesdale, L. K.; Dietrich, C. O. J. Am. Chem.
Soc. 1976, 98, 269-270. (c) Kresze, G.; Braxmeier, H.; M u¨ nsterer, H. Org.
Synth. 1987, 65, 159-165. (d) Katz, T. J.; Shi. S. J. Org. Chem. 1994, 59,
98.4%). Moreover, we could detect (by GC-MS) the formation
of benzene and cyclohexadiene in the volatile fraction after the
end of the reaction. The same two products were not present
in the starting solvent, and their formation indicates that the
substrate itself is responsible for at least part of the aniline
formed, but moisture in the undried solvent plays a negligible
role. The higher selectivity obtained with the purified substrate
also indicates that, although the commercial olefin is a suitable
substrate, it contains some impurities which lower the selectivity,
affording unidentified, high-boiling products.
8
297-8298.
(
4) (a) Liebeskind, L. S.; Sharpless, K. B.; Wilson, R. D.; Ibers, J. A. J.
Am. Chem. Soc. 1978, 100, 7061-7063. (b) Møller, E. R.; Jørgensen, K.
A. J. Am. Chem. Soc. 1993, 115, 11814-11822.
(
5) Mahy, J. P.; Bedi, G.; Battioni, P.; Mansuy, D. Tetrahedron Lett.
1
988, 29, 1927-1930.
(
6) (a) Srivastava, R. S.; Nicholas, K. M. Tetrahedron Lett. 1994, 35,
8
5
739-8742. (b) Srivastava, R. S.; Nicholas, K. M. J. Org. Chem. 1994,
9, 5365-5371. (c) Srivastava, A.; Ma, Y.; Pankayatselvan, R.; Dinges,
W.; Nicholas, K. M. J. Chem. Soc., Chem. Commun. 1992, 853-854. (d)
Johannsen, M.; Jørgensen, K. A. J. Org. Chem. 1995, 60, 5979-5982. (e)
Johannsen, M.; Jørgensen, K. A. J. Org. Chem. 1994, 59, 214-216.
We also examined the effect of changing the substituent in
the para position of the aryl rings of the ligand. In all the cases,
the conversion was complete, but the selectivity in allylamine
followed the order R ) H > Me > OMe > Cl (entries 5 and
(
7) (a) Bassoli, A.; Rindone, B.; Cenini, S. J. Mol. Catal. 1991, 66, 163-
1
70. (b) Bassoli, A.; Rindone, B.; Tollari, S.; Cenini, S.; Crotti, C. J. Mol.
Catal. 1990, 60, 155-163.
8) (a) Intramolecular reactions of a nitro group and an olefin under CO
(
pressure have already been reported by us and others (see ref 8b-g for
some examples) to afford several types of heterocycles. However, in this
case, the attack occurs at an olefin, rather than allylic carbon (see also later).
8
-10). The less basic ligand clearly disfavors the formation
of the allylamine, but there is no correlation with the Hammet
(b) Crotti, C.; Cenini, S.; Rindone, B.; Tollari, S. J. Chem. Soc., Chem.
σ constant. Use of 3,4,7,8-tetramethyl-1,10-phenanthroline
Commun. 1986, 784-785. (c) Crotti, C.; Cenini, S.; Todeschini, R.; Tollari,
S. J. Chem. Soc., Faraday Trans. 1991, 87, 2811-2820. (d) Akazone, M.;
Kondo, T.; Watanabe, Y. Chem. Lett. 1992, 769-772. (e) Tollari, S.; Cenini,
S.; Crotti, C.; Giannella, E. J. Mol. Catal. 1994, 87, 203-214. (f) Tollari,
S.; Cenini, S.; Ragaini, F.; Cassar, L. J. Chem. Soc., Chem. Commun. 1994,
(
TMPhen) as the ligand in place of DIAN-R gave much poorer
results (entry 7). Phosphines are even less efficient as ligands,
(9) At the moment, we have not yet identified the other products of the
catalytic reactions, which are not observable by GC.
(10) Ragaini, F.; Cenini, S.; Tollari, S. J. Mol. Catal. 1993, 85, L1-L5.
1
741-1742. (g) Annunziata, R.; Cenini, S.; Palmisano, G.; Tollari, S. Synth.
Commun. 1996, 26, 495-501.
S0002-7863(95)04158-8 CCC: $12.00 © 1996 American Chemical Society