Transposition of allylic alcohols into carbonyl compounds catalyzed by rhodium-phosphinine complexes

Article abstract of DOI:10.1055/s-2006-948180

The isomerization of a variety of allylic alcohols with formation of the corresponding saturated carbonyl compounds is readily accomplished by a new catalyst system comprising rhodium and a trisubstituted phosphinine (phosphabenzene derivative), especially when the Rh complex is activated by hydrogen prior to the transposition reaction. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-948180

LETTER
2127
Transposition of Allylic Alcohols into Carbonyl Compounds Catalyzed by
Rhodium–Phosphinine Complexes
T
M
ransposition of
A
llyli
a
c
Alcoholsnfred T. Reetz,* Hongchao Guo
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim/Ruhr, Germany
Fax +49(208)3062985; E-mail: reetz@mpi-muelheim.mpg.de
Received 3 May 2006
R3
R3
Abstract: The isomerization of a variety of allylic alcohols with
R1
R4
OH
metal catalyst
R1
R4
formation of the corresponding saturated carbonyl compounds is
readily accomplished by a new catalyst system comprising rhodium
and a trisubstituted phosphinine (phosphabenzene derivative), espe-
cially when the Rh complex is activated by hydrogen prior to the
transposition reaction.
R2
R2
O
3
4
Scheme 1 Transition-metal-catalyzed isomerization of allylic alco-
Key words: green chemistry, homogeneous catalysis, isomeriza-
tion, phosphorus, rhodium
hols with formation of carbonyl compounds
In the present study sixteen allylic alcohols 3a–p
(
Figure 2) were subjected to isomerization. Based on pre-
We recently showed that the use of mixtures of monoden-
tate P-ligands provides a combinatorial means to control
diastereoselectivity in Rh-catalyzed olefin hydrogenation
vious work using Rh catalysts or other transition-metal
analogues, it is known that the reaction becomes more
difficult as the degree of substitution around the olefinic
double bond increases.
2,3
1
of chiral allylic alcohols. The members of the library of
ligands used included simple aryl- and alkylphosphines,
phosphinites, phosphites and phosphinines (phosphaben-
zenes). In most cases a side product was observed, namely
a saturated ketone resulting from an internal redox pro-
cess. When using the triaryl-substituted phosphinine 1
OH
OH
OH
OH
(
Figure 1), this undesired isomerization was most promi-
3a
3b
3d
3c
1
nent. Since the targeted transition-metal-catalyzed
isomerization of allylic alcohols is an atom-economical
method of significant synthetic value, we decided to
focus our attention on this process (Scheme 1). Here we
show that Rh complexes of ligand 1, especially when ac-
OH
2
,3
OH
OH
3
e
3f
3g
tivated by H , are in fact excellent catalysts, surpassing
2
the efficiency of traditional analogues based on triphen-
ylphosphine (2). This finding constitutes yet another ex-
ample of the useful application of phosphinines as ligands
OH
OH
OH
4
in transition metal-catalyzed reactions, originally intro-
3h
3i
3j
5
duced by Breit in selective hydroformylation and by
Zennek and Mathey in Fe-catalyzed pyridine synthesis.6
OH
OH
OH
3
l
3
k
3m
3p
Ph
Ph
Ph
OH
P
OH
OH
P
3
3
n
3o
Figure 2
1
2
Figure 1
Exploratory experiments were first performed with allylic
alcohol 3c. In procedure A, Rh(NBD) BF (NBD = nor-
2
4
bornadiene) was treated with two equivalents of phosphi-
nine 1 or phosphine 2 under an Ar atmosphere and stirred
for 30 minutes. Then the complex was used as a catalyst
in the isomerization of 3c under various conditions. In
SYNLETT 2006, No. 13, pp 2127–2129
1
7
.0
8
.2
0
0
6
Advanced online publication: 09.08.2006
DOI: 10.1055/s-2006-948180; Art ID: G14506ST
Georg Thieme Verlag Stuttgart · New York
©

2
128
M. T. Reetz, H. Guo
LETTER
procedure B, the same protocol was applied, except that It can be seen that the activation of the Rh complex with
following the treatment of the Rh salt with the respective H prior to catalysis (Method B) results in a much more
2
ligand, the mixture was stirred under 1.3 bar H for 30 active catalyst, especially when using dioxane as the sol-
2
minutes with formation of an activated species, presum- vent (e.g., entry 2 vs. 1, or entry 4 vs. 3). The side-prod-
ably a Rh hydride. Following H displacement by Ar, the ucts include various reduction and/or coupling products,
2
activated form of the Rh complex was used in catalysis. which reduce selectivity. We then proceeded to test the
Table 1 shows the results.
other allylic alcohols using Method B, although full
optimization in each case was not attempted (Table 2).7
a
Table 1 Optimization of the Isomerization 3c → 4c Using 2 mol% of Rh Complexes
Entry
Ligand
Method
Solvent
Dioxane
Dioxane
Dioxane
Dioxane
CH Cl
Temp. (°C)
Time (h)
Conv. (%)
Selectivity (%)
1
2
3
4
5
6
2
2
1
1
1
1
1
A
B
A
B
A
B
B
60
60
60
60
23
23
23
12
12
12
1
30
91
30
77
30
100
100
100
100
72
100
1
16
1
2
2
2
2
CH Cl
17
2
7
CH Cl
16
100
2
a
Method A: no H pretreatment. Method B: H pretreatment. Rh(NBD) BF used in all cases; conversion and selectivity by GC and GC-MS
2
2
2
4
determinations.
a
Table 2 Isomerization of Allylic Alcohols 3a–p with Formation of 4a–p Using 2 mol% of H Activated Rh(1) BF
4
2
2
Entry
Allylic alcohol
Solvent
CH Cl
Temp. (°C)
Time (h)
0.5
1
Conv. (%)
100
100
100
100
100
100
100
100
85
Selectivity (%)
1
2
3
4
5
6
7
8
9
3a
3b
3c
3d
3e
3f
23
60
60
60
23
23
60
23
60
23
60
60
23
60
23
23
60
60
60
100
93
2
2
Dioxane
Dioxane
Dioxane
CH Cl
1
100
100
100
98
3.5
0.5
0.5
1
2
2
2
CH Cl
2
3g
3g
3h
3i
Dioxane
CH Cl
97
6
81
2
2
Dioxane
CH Cl
12
0.5
12
6
84
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
9
100
51
100
8
2
2
3j
Dioxane
Dioxane
CH Cl
3k
3k
3l
100
100
99
100
90
16
1
2
2
Dioxane
CH Cl
98
3l
16
0.5
2
73
72
2
2
2
3m
3n
3o
3p
CH Cl
100
100
19
100
100
100
33
2
Dioxane
Dioxane
Dioxane
12
12
1
70
a
Method B; conversion and selectivity by GC and GC-MS determinations.
Synlett 2006, No. 13, 2127–2129 © Thieme Stuttgart · New York

LETTER
Transposition of Allylic Alcohols
2129
As shown in Table 2, allylic alcohols with diverse sub- References and Notes
stitution patterns including monosubstituted (entries 1, 2)
(
(
1) Reetz, M. T.; Guo, H. Beilstein J. Org. Chem. 2005, 1:3.
2) Reviews: (a) Uma, R.; Crévisy, C.; Grée, R. Chem. Rev.
003, 103, 27. (b) van der Drift, R. C.; Bouwman, E.; Drent,
E. J. Organomet. Chem. 2002, 650, 1.
disubstituted (entries 3–10), and trisubstituted substrates
entries 12, 17), can be transformed smoothly into the cor-
(
2
responding saturated aldehydes or ketones in the presence
of H activated Rh(1) BF under mild conditions. Excep-
(3) Leading studies regarding Rh- and Ru-catalyzed
isomerization of allylic alcohols: (a) Trost, B. M.;
Kulawiec, R. J. J. Am. Chem. Soc. 1993, 115, 2027.
2
2
4
tions are substrates 3j (entry 11) and 3p (entry 19), which
provide rather sensitive aldehydes, as well as the highly
substituted allylic alcohol 3o (entry 18). Of particular note
is the efficient isomerization of the trisubstituted allylic
alcohol 3n (entry 17). This compound (or analogues) is
isomerized efficiently only by very few catalysts.2a,3g,3k
(b) McGrath, D. V.; Grubbs, R. H. Organometallics 1994,
13, 224. (c) Markó, I. E.; Gautier, A.; Tsukazaki, M.; Llobet,
A.; Plantalech-Mir, E.; Urch, C. J.; Brown, S. M. Angew.
Chem. Int. Ed. 1999, 38, 1960; Angew. Chem. 1999, 111,
2126. (d) Slugovc, C.; Rüba, E.; Schmid, R. D.; Kirchner, K.
Organometallics 1999, 18, 4230. (e) de Bellefon, C.;
Caravieilhes, S.; Kuntz, G. C. R. Acad. Sci., Ser. IIc: Chim.
Extensive structural studies of the activated Rh complexes
involving ligands 1 and 2 have not been performed. How-
ever, preliminary NMR and ESI-MS experiments show
the presence of species of the type Rh(1) [H] BF in
2000, 3, 607. (f) Tanaka, K.; Fu, G. C. J. Org. Chem. 2001,
66, 8177. (g) Uma, R.; Davies, M. K.; Crévisy, C.; Grée, R.
Eur. J. Org. Chem. 2001, 3141. (h) Cadierno, V.; García-
Garrido, S. E.; Gimeno, J. Chem. Commun. 2004, 232.
2
n
4
which NBD has been cleaved by hydrogenation. Appar-
ently, the Rh hydrides are more active than the starting Rh
(
i) Martín-Matute, B.; Bogár, K.; Edin, M.; Kaynak, F. B.;
Bäckvall, J.-E. Chem. Eur. J. 2005, 11, 5832. (j) Crochet,
P.; Díez, J.; Fernández-Zúmel, M. A.; Gimeno, J. Adv. Synth.
Catal. 2006, 348, 93. (k) Ito, M.; Kitahara, S.; Ikariya, T. J.
Am. Chem. Soc. 2005, 127, 6172. (l) Takai, Y.; Kitaura, R.;
Nakatani, E.; Onishi, T.; Kurosawa, H. Organometallics
2005, 24, 4729. (m) Cadierno, V.; García-Garrido, S. E.;
Gimeno, J.; Varela-Álvarez, A.; Sordo, J. A. J. Am. Chem.
Soc. 2006, 128, 1360.
complex prior to treatment with H . The reason for this
2
activation is unclear at this time, but the observation
suggests that similar activation of other transition-metal
2
,3
complexes used in the isomerization may also be possi-
ble. The mechanism may be different from Ru-catalyzed
isomerizations.3
In summary, a new and active catalyst system for the
isomerization of allylic alcohols with formation of the
saturated carbonyl compounds has been developed. It is
based on the Rh complexes of a trisubstituted phosphinine
(
4) Reetz, M. T.; Li, X. Angew. Chem. Int. Ed. 2005, 44, 2962;
Angew. Chem. 2005, 117, 3022.
(5) (a) Breit, B. Chem. Commun. 1996, 2071. (b) Breit, B.;
Winde, R.; Mackewitz, T.; Paciello, R.; Harms, K. Chem.
Eur. J. 2001, 7, 3106.
6) Knoch, F.; Kremer, F.; Schmidt, U.; Zenneck, U.; LeFloch,
P.; Mathey, F. Organometallics 1996, 15, 2713.
7) General Procedure for the Isomerization of Allylic
Alcohol.
ligand. For optimal results, activation by H treatment of
2
(
the Rh–phosphinine complex is best carried out prior to
7
the isomerization reaction.
(
A dry 5-mL Schlenk flask under an atmosphere of argon was
charged with a 5.4 mM solution of P-ligand (0.5 mL) in dry
CH Cl and a 5.4 mM solution of [Rh(NBD) ]BF (0.25 mL)
Acknowledgment
Generous support by the Fonds der Chemischen Industrie is grate-
fully acknowledged.
2
2
2
4
in CH Cl . The mixture was stirred for 30 min at r.t., then
2
2
stirred for an additional 30 min under 1.3 bar H . The CH Cl
2
2
2
and H were removed by Ar displacement under reduced
2
pressure, then 0.5 mL of CH Cl and a 67.5 mM solution of
2
2
an allylic alcohol in CH Cl (1 mL) were added. The
2
2
isomerization was carried out for the periods given. The
reaction solution was passed through a small amount of
silica gel and selectivity and conversion were determined by
gas chromatography (GC and GC-MS).
Synlett 2006, No. 13, 2127–2129 © Thieme Stuttgart · New York