Ruthenium-catalyzed enaminoketone formation from propargyl alcohols

Article abstract of DOI:10.1055/s-2006-947357

Monomeric ruthenium(0) complexes containing electronically coupled dienone ligands were found to catalyze the formation of enaminoketones from propargyl alcohols. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-947357

LETTER
1847
Ruthenium-Catalyzed Enaminoketone Formation from Propargyl Alcohols
E
naminoketone
d
from Propa
g
rgyl
A
lcoho
a
Department of Organic Chemistry, University of Braunschweig, Hagenring 30, 38106 Braunschweig, Germany
Fax +49(5531)3915388; E-mail: e.haak@tu-bs.de
Received 13 April 2006
This paper is dedicated to Prof. Henning Hopf.
amino-propenone (Z-7a) and small amounts of the hydro-
Abstract: Monomeric ruthenium(0) complexes containing elec-
tronically coupled dienone ligands were found to catalyze the
formation of enaminoketones from propargyl alcohols.
amination product 8a. Using the sterically more hindered
complex 4b accelerated consumption of the educts is ob-
served but the b-aminoketone 9a is formed as a second
by-product. The aliphatic propargyl alcohol 5b and the
internal propargyl alcohol 5c show similar reactivity to
yield the enaminoketones Z-10 and Z-11, respectively
Key words: aminations, enaminoketones, homogenous catalysis,
propargyl alcohols, ruthenium
(
Scheme 2).
5
The Shvo complex [{(h -Ph C CO) H}Ru ((CO) )(m-H)]
4
4
2
2
4
1
(
1) catalyzes a broad number of homogeneous hydrogen
OH
Ph
transfer reactions such as the disproportionation of alde-
+
aniline
2
3
hydes to esters, the reduction of aldehydes and ketones,
4
,5
5a
6a
the Oppenhauer-type oxidation of alcohols and amines,
6
,7
3.0 mol% 4a or 4b
toluene, 100 °C, 5 h
the racemization of alcohols and amines and the dehy-
drogenation of alcohols without hydrogen acceptors.8
Ph
H
O
N
O
NHPh O
Complex 2, which is formed from 1 as well as from
monomeric complexes of type 4, represents the reactive
+
PhHN
+
Ph
Ph
Ph
9
species in the oxidation step (Scheme 1).
(
Z)-7a
8a
9a
using catalyst 4a: 49% (Z)-7a, 10% 8a, 0% 9a
using catalyst 4b: 55% (Z)-7a, 27% 8a, 14% 9a
H
Ph
Ph
O
O
Ph
Ph
R
OH
Ph
H
Ph
Ph
R
O
3.0 mol% 4a
Ph
Ph
N
O
+
aniline
Ru
Ph
CO
Ru
Ph
OC
Ru
OC
OC
toluene, 100 °C, 5 h
H
CO
CO
CO
(Z)-10 (47%)
1
5
b
6a
4
4
a R = Me
b R = Ph
OH
Ph
H
3.0 mol% 4a
N
O
+
aniline
–
CO
toluene, 100 °C, 5 h
Ph
Ph
Ph
5
c
6a
(Z)-11 (52%)
Ph
Ph
Ph Ph
+
Ph
OH
Ph
R
Scheme 2 Enaminoketone formation from aniline 6a
O
R
O
Ph
OC
Ru
Ru
Ru
OC
OC
OC
OC
H
OC
The variation of the amine component leads to a broad
range in reactivity. Pyrrolidine (6b), L-proline methylester
2a
3
2
(
(
6c), allylamine (6d) and L-aspartic acid dimethylester
6e) show relativly high and benzhydrylamine (6f)
Scheme 1 Formation of the coordinatively unsaturated species 2
moderate reactivity. The benzylic amines 6g and 6h, (R)-
-cyclohexylethylamine (6i), tryptamine (6j), L-tryp-
During studies on the development of new transition-
metal-catalyzed aminations of propargyl alcohols, forma-
tion of enaminoketones catalyzed by the complexes 4a or
1
tophan methylester (6k) and L-alanine methylester (6l)
react slowly. In general, primary amines form the hydro-
gen bridged Z-enaminoketones, secondary amines give
the sterically more favored E-enaminoketones. In case of
the proline derivative (E)-7c a rotational barrier regarding
4
b was detected, whereas no transformation of propargyl
alcohols could be observed without the presence of an
amine.
1
-Phenyl-2-propin-1-ol (5a) reacts with aniline 6a in the the C–N bond is observed. By-products were not detected
presence of 3.0 mol% 4a to yield (Z)-1-phenyl-3-phenyl- and unreacted starting material could be recovered in all
cases (Scheme 3, Table 1).
The mechanism of this new transformation is still under
investigation. Since the propargyl alcohol can be recov-
ered quantitatively if the reaction is performed without an
SYNLETT 2006, No. 12, pp 1847–1848
Advanced online publication: 24.07.2006
DOI: 10.1055/s-2006-947357; Art ID: G12806ST
0
1
.0
8
.2
0
0
6
©
Georg Thieme Verlag Stuttgart · New York

1
848
E. Haak
LETTER
R
H
Acknowledgment
N
O
Constant support by the Fonds der Chemischen Industrie is grate-
fully acknowledged.
OH
Ph
3.0 mol% 4a
amine 6
Ph
Ph
(
Z)-7
toluene, 100 °C, 8 h
O
R1
References and Notes
5a
N
R2
(1) (a) Shvo, Y.; Czarkie, D. J. Am. Chem. Soc. 1986, 108,
(E)-7
7400. (b) Jung, H. M.; Shin, S. T.; Kim, Y. H.; Kim, M.-J.;
Scheme 3 Enaminoketone formation from 5a and various amines
Park, J. Organometallics 2001, 20, 3370. (c) Jung, H. M.;
Choi, J. H.; Lee, S. O.; Kim, Y. H.; Park, J. H.; Park, J.
Organometallics 2002, 21, 5674.
(
(
(
2) Menashe, N.; Shvo, Y. Organometallics 1991, 10, 3885.
3) Shvo, Y.; Czarkie, D. J. Organomet. Chem. 1986, 315, C25.
4) (a) Almeida, M. L. S.; Beller, M.; Wang, G.-Z.; Bäckvall, J.-
E. Chem. Eur. J. 1996, 2, 1533. (b) Almeida, M. L. S.;
Kocovsky, P.; Bäckvall, J.-E. J. Org. Chem. 1996, 61, 6587.
Table 1 Ruthenium-Catalyzed Enaminoketone Formation from 5a
Amine
Product
E-7b
E-7c10
Z-7d10
Z-7e
Yield (%)
Pyrrolidine (6b)
48
65
53
49
39
25
14
20
11
17
16
(
c) Csjernyik, G.; Ell, A. H.; Fadini, L.; Pugin, B.; Bäckvall,
L-Proline methylester (6c)
Allylamine (6d)
J.-E. J. Org. Chem. 2002, 67, 1657.
(
(
5) Ell, A. H.; Samec, J. S. M.; Brasse, C.; Bäckvall, J.-E. Chem.
Commun. 2002, 1144.
6) (a) Larsson, A. L. E.; Persson, B. A.; Bäckvall, J.-E. Angw.
Chem., Int. Ed. Engl. 1997, 36, 1211. (b) Larsson, A. L. E.;
Persson, B. A.; Ray, M. L.; Bäckvall, J.-E. J. Am. Chem. Soc.
L-Aspartic acid dimethylester (6e)
Benzhydrylamine (6f)
Benzylamine (6g)
Z-7f
1999, 121, 1645. (c) Pamies, O.; Bäckvell, J.-E. Chem. Rev.
Z-7g
Z-7h
Z-7i
2003, 103, 3247.
(7) Pamies, O.; Ell, A. H.; Samec, J. S. M.; Hermanns, N.;
Bäckvell, J.-E. Tetrahedron Lett. 2002, 43, 4699.
(8) Choi, J. H.; Kim, N.; Shin, Y. J.; Park, J. H.; Park, J.
Tetrahedron Lett. 2004, 45, 4607.
(
(
(
R)-a-Methylbenzylamine (6h)
R)-1-Cyclohexylethylamine (6i)
9) (a) Blum, Y.; Shvo, Y.; Chodosh, D. F. Inorg. Chim. Acta
Tryptamine (6j)
Z-7j
1985, 97, C25. (b) Blum, Y.; Shvo, Y.; Czarkie, D.;
L-Tryptophan methylester (6k)
L-Alanine methylester (6l)
Z-7k
Z-7l
Rahamim, Y. Organometallics 1985, 4, 1459. (c) Blum, Y.;
Shvo, Y. Isr. J. Chem. 1984, 24, 144.
(
10) Characterization Data for Typical Enaminoketones.
1
Compound E-7c: C H NO , yellow oil (rotamers 4:1). H
1
5
17
3
NMR (300 MHz, CDCl ): d = 1.90–2.34 (m, 4 H), 3.50–3.55
3
amine and no hydrid acceptor is present in the reaction
mixture, an initial isomerization process or the established
mechanism of hydrogen transfer reactions mediated by
the Shvo complex 1 seem not to take place here. Due to
the fact that the internal propargyl alcohol (5c) show
similar reactivity to the terminal ones 5a and 5b an initial
activation of the alkyne terminus is unlikely as well. The
role of the amine in the catalytic cycle remains crucial; it
may be involved in the oxidation step or in the regenera-
tion of the active catalytic species.
(m, 2 H), 3.75 (s, 3 H), 4.16 and 4.29 (t, J = 8.1 Hz, 1 H),
5
.67 and 5.77 (d, J = 12.4 Hz, 1 H), 7.37–7.46 (m, 3 H),
1
3
7.87–8.01 (m, 3 H). C NMR (75 MHz, DEPT, CDCl ):
3
d = 23.2 and 25.1 (CH ), 27.5 and 29.7 (CH ), 45.1 and 46.0
2
2
(
CH ), 52.5 (CH ), 60.4 and 60.9 (CH), 92.9 and 94.8 (CH),
2 3
1
1
27.4 and 127.5 (CH), 127.9 and 128.0 (CH), 130.6 and
31.0 (CH), 140.0 and 140.5 (C), 149.3 and 149.8 (CH),
166.3 and 172.1, 188.8 (C). IR: 3056, 3024, 2956, 2878,
1741, 1662, 1633, 1580, 1539, 1449, 1364, 1340, 1304,
1
274, 1209, 1166, 1090, 1051, 1026, 1008, 991, 925, 893,
–
1
837, 758, 706, 621, 557 cm . MS (EI): m/z (%) = 259 (45)
+
[
M ], 200 (100), 172 (34), 154 (58), 105 (70), 77 (54), 70
In summary, a new catalytic method to generate the syn-
thetically important enaminoketones from easy and in a
wide range accessible propargyl alcohols is presented.
The simple synthesis and high stability of complexes of
type 4 make them attractive, easy to handle and practical
catalysts.
(36). HRMS: m/z calcd: 259.12085; found: 259.12007.
Compound Z-7d: C12H13NO, yellow oil. H NMR (400
1
MHz, CDCl ): d = 3.89 (tt, J = 5.6, 1.6 Hz, 2 H), 5.21 (dq,
3
J = 10.2, 1.4 Hz, 1 H), 5.27 (dq, J = 17.1, 1.7 Hz, 1 H), 5.75
(
6
(
d, J = 7.5 Hz, 1 H), 5.90 (ddt, J = 17.1, 10.3, 5.1 Hz, 1 H),
.93 (dd, J = 12.8, 7.5 Hz, 1 H), 7.38–7.44 (m, 3 H), 7.88
dd, J = 8.2, 1.4 Hz, 2 H), 10.3 (br s, NH). C NMR (100
13
MHz, DEPT, CDCl ): d = 51.0 (CH ), 90.7 (CH), 117.1
3
2
(
CH ), 127.0 (CH), 128.2 (CH), 130.9 (CH), 134.2 (CH),
2
1
2
1
6
1
39.7 (C), 154.0 (CH), 190.1 (C). IR: 3271, 3059, 3027,
921, 2855, 1627, 1582, 1541, 1499, 1476, 1442, 1363,
272, 1227, 1205, 1161, 1048, 1021, 988, 922, 867, 734,
99, 554 cm . MS (EI): m/z (%) = 187(58) [M ], 186 (39),
05 (100), 82 (89), 77 (55). HRMS: m/z calcd: 187.09972;
General Procedure
Propargyl alcohol (1 mmol) and the amine (1 mmol) were dissolved
in toluene (0.5 mL) and the catalyst (0.03 mmol) was added. The
mixture was stirred at 100 °C for 5 h or 8 h under argon. Using
allylamine (6d) the reaction was performed in a closed tube.
Aqueous work-up and chromatography on silica furnished the
enaminoketones 7.
–
1
+
found: 187.09941.
Synlett 2006, No. 12, 1847–1848 © Thieme Stuttgart · New York