Reductive coupling of allylic esters with carbonyl compounds mediated by the mischmetall/[SmI2/Pd0cat.′] cat. system

Article abstract of DOI:10.1002/ejoc.200500291

The mischmetall/[SmI₂/Pd⁰_cat.′] _cat. system has been used to mediate the allylation of ketones using a variety of allylic esters (acetates, carbonates and phosphates). Thus, a "two-stage catalysis" has been carried out using SmI₂ and Pd(PPh₃)₄ in catalytic amounts together with mischmetall (an alloy of the light lanthanides) as a co-reductant. A catalytic scheme that takes into account previously reported reactions of SmI₂/Pd ⁰_cat. and mischmetall/SmI_2,Cat. systems is proposed. It has also been shown that palladium complexes catalyse the addition of organolanthanide species to ketones. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

Full text of DOI:10.1002/ejoc.200500291

FULL PAPER
Reductive Coupling of Allylic Esters with Carbonyl Compounds Mediated by
0
the Mischmetall/[SmI /Pd
]
System
2
cat.Ј cat.
[a]
[a]
[a]
Sédami Médégan, Florence Hélion, and Jean-Louis Namy*
Keywords: Allylation / Catalysis / Mischmetall / Samarium / Palladium
The mischmetall/[SmI
mediate the allylation of ketones using a variety of allylic
esters (acetates, carbonates and phosphates). Thus, a “two-
2
/Pd0cat.Ј
]
cat. system has been used to
scheme that takes into account previously reported reactions
of SmI /Pd cat. and mischmetall/SmI2,cat. systems is proposed.
2
It has also been shown that palladium complexes catalyse
the addition of organolanthanide species to ketones.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
0
stage catalysis” has been carried out using SmI
2
and
Pd(PPh in catalytic amounts together with mischmetall (an
3 4
)
alloy of the light lanthanides) as a co-reductant. A catalytic
Introduction
Mischmetall, an alloy of the light lanthanides (Ce, La,
The reduction of allylic and propargylic esters in the Nd and Pr), also known as cerium mixed metal, is obtained
presence of an alcohol, as well as the coupling of these sub- from bastnaesite (a lanthanide ore). It is an industrial mate-
strates with carbonyl compounds, using a combination of rial used in steelmaking which is available in large quantities
0
[1–10]
SmI and catalytic Pd have been widely studied.
Some at a low price since the elements are not separated (an ex-
pensive process).
2
examples of these reactions are shown in Scheme 1.
Scheme 1.
In these reactions, the formation of a (π-allyl)palladium
species, which is subsequently reduced to an organosamar-
0
ium compound with the regeneration of Pd , is likely
(Scheme 2).
In addition, we have recently reported the use of
mischmetall as a co-reductant in the catalytic reactions of
some organic substrates with samarium diiodide.[
11,12]
For
[
13]
example, Barbier-type reactions have been studied
(Scheme 3).
Scheme 2.
[
a] Laboratoire de Catalyse Moléculaire, associé au CNRS,
ICMMO, Bat 420, Université Paris-Sud,
9
1405, Orsay, France
Two mechanisms for this transformation are conceivable
(Figures 1 and 2). In the first mechanism (Figure 1), an or
Fax: +33-1-69154680
E-mail: jelonamy@icmo.u-psud.fr
Eur. J. Org. Chem. 2005, 4715–4722
DOI: 10.1002/ejoc.200500291
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4715

S. Médégan, F. Hélion, J.-L. Namy
FULL PAPER
Scheme 3.
ganosamarium compound, RSmIX (or RSmX or RSmI ) marium species are unstable, leads us to conclude that the
2
2
is formed first. Its addition to a carbonyl compound gives second mechanism is more plausible.
a samarium alkoxide. This in turn, through reduction/trans-
We wondered whether it would be possible to allylate
metallation with the lanthanide, gives lanthanide alkoxide carbonyl compounds with allylic esters using the mischmet-
0
with the regeneration of SmI (or SmX ). In the second all/[SmI /Pd
]
system (with mischmetall as a co-re-
2
2
2
cat.Ј cat.
mechanism (Figure 2), the initially formed RSmIX reacts ductant, catalytic amounts of SmI2 with respect to
0
with lanthanide to give another organometallic compound mischmetall and catalytic amounts of Pd with respect to
(
LnR ; Ln ϶ Sm) through reduction/transmetallation with SmI ). This system is comparable to the mischmetall/[SmI /
3
2
2
the regeneration of SmI . This organolanthanide com- NiI
pound then adds to the carbonyl compound to furnish an and would amount to a “two-stage catalysis”. This cata-
] one, which has been used to alkylate lactones,
2
2,cat.Ј cat.
[
14]
alkoxide.
lytic process could also be related to “concurrent tandem
catalysis” since it involves the cooperative action of two
catalytic cycles in a single reactor.
[
15]
Results and Discussion
A variety of allylic acetates (with the exception of allyl
acetate) have been used to allylate carbonyl compounds
(
ketones and aldehydes); an intramolecular reaction has
[
2]
also been reported. To the best of our knowledge the use
of allylic carbonates in these reactions have not been tested
whereas allylic phosphates have been studied but in the ab-
sence of Pd . However, it has been mentioned that these
latter substrates should be more reactive in the presence of
0
[16]
Figure 1. Catalytic scheme I.
[
17]
Pd(PPh ) .
3
4
Since our aim was to test a large variety of substrates
0
in reactions mediated by the mischmetall/[SmI /Pd
]
2
cat.Ј cat.
system, we first studied the reactions of some allylic esters
0
(
carbonates, phosphates and acetates) using the SmI /Pd
2 cat.
system.
Some examples of the allylation rections of ketones are
gathered in Table 1.
With cinnamyl carbonate, the yields of the homoallylic
alcohols were satisfactory. Except in the case of 5-nonanone
(Entry 3), mixtures of two homoallylic alcohols were ob-
tained with the linear isomer (product A) as the major pro-
duct. In all cases, dienes arising from the coupling of the
cinnamyl moiety were formed as by-products (1,4-di-
phenylhexa-1,5-diene, 1,6-diphenylhexa-1,5-diene and 3,4-
diphenylhexa-1,5-diene). The alcohols were also observed
in the absence of palladium; the reaction was slower but the
A/B ratios are only slightly dependent on the presence of
the catalyst (Entries 1 and 2).
Figure 2. Catalytic scheme II.
Evidence[13] that allylation reactions with cinnamyl bro-
With allyl carbonate the yields of the expected alcohols
mide can be performed sequentially (addition of cinnamyl were lower; hexa-1,5-diene was almost certainly the main
bromide, then the ketone), even though trivalent allylic sa- by-product, but unfortunately this compound (b.p. 59.5°C)
4716
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2005, 4715–4722

Reductive Coupling of Allylic Esters with Carbonyl Compounds
Table 1. Allylation reactions with allylic esters.[a]
FULL PAPER
1
2
Entry
1
Y
R , R
Isolated yield (%) of A + B (A/B)
R = phenyl
R = H (A = B)
–OC(O)
–OC(O)
–OC(O)
–OC(O)
–OC(O)
–OPO(OC
–OPO(OC
2
2
2
2
2
CH
CH
CH
CH
CH
3
3
3
3
3
)
)
–(CH
–(CH
2
)
5
–
–
74 (2.8)
49 (2.65)
68 (0.8)
78 (3.12)
63 (6.54)
64 (2.24)
51 (2.40)
77 (2.44)
27
n.d.
45
52
[
b]
2
2
)
5
3
4
5
n-C
CH
CH
4
H
3
9
, n-C
, n-C
4
H
13
9
6
H
C
6
H
5
2
CH
2
, CH
–
–
–
3
complex mixture
[
c]
6
2
H
H
5
2
–(CH
–(CH
–(CH
2
2
2
)
5
)
5
)
5
n.d.
n.d.
n.d.
[
d]
7
8
2
5
2
[
c]
–OCOCH
3
[a] Conditions: THF, 20°C, 3 h. [b] Without Pd(Ph
3
)
4
; 16 h. [c] Reaction time: 1 h. [d] Without Pd(PPh
3 4
) ; 1 h.
0
could not be observed easily under our experimental condi- (mischmetall/SmI /Pd ) being essential (Entries 9 and 10).
2
tions. With cinnamyl phosphate (Entries 6 and 7) the pres- Mixtures of homoallylic alcohols (linear and branched)
0
ence of Pd led to a significant increase in the yield of were formed; the A/B ratio was close to 1 with a slight pre-
0
alcohol (64% in the presence of Pd compared with 51% in ponderance of the linear isomer A. The use of 2.5 mol-%
its absence) but the A/B ratios were similar (2.24 and 2.40). Pd(PPh ) was found to give satisfactory results. Note that
3
4
Unexpectedly, we obtained better isolated yields of the a sequential procedure failed, the expected alcohols not be-
alcohols than has previously been reported in the literature ing detected; instead, 1,4-diphenylhexa-1,5-diene was ob-
51 compared with 37%).[ With cinnamyl acetate and cy- served as a single product (Scheme 4). This result is in con-
16]
(
clohexanone, (Entry 8), in contrast to previously reported trast with the coupling reaction between cinnamyl bromide
[
5]
results,
alcohols (A/B = 2.44).
Coupling between cinnamyl acetate and cyclohexanone shown in Entry 2 were found to give the best results
we obtained linear and branched isomeric and carbonyl compounds mediated by the mischmetall/
[
13]
SmI2,cat.system.
Finally, the experimental conditions
0
mediated by mischmetall/[SmI /Pd
]
was studied un- (Table 2).
2
cat.Ј cat.
der a variety of experimental conditions (Table 2).
It is also important to note that the A/B ratios obtained
This system could be used to carry out this reaction ef- under both samarium diiodide catalytic (Table 2, Entry 2)
ficiently, all the components of the catalytic system and stoichiometric conditions (Table 1, Entry 8) differ sig-
Table 2. Allylation of cyclohexanone under a variety of experimental conditions.[a]
3 4
Pd(PPh )
[mol-%][c] Isolated yield (%) A + B (A/B)
Entry
Ln[b]
Cinnamyl acetate [mmol]
Cyclohexanone [mmol]
1
2
3
mischmetall
mischmetall
mischmetall
mischmetall
mischmetall
mischmetall
mischmetall
mischmetall
mischmetall
mischmetall
La
3
4
4
5
5
4
5
4
5
5
4
4
4
5
4
4
3.5
3.5
4
3.5
4
3.5
3.5
4
4
4
2.5
2.5
2.5
2.5
2.5
2.5
1
1
2.5
0
49 (1.2)
68 (1.12)
60 (1.04)
62 (1.0)
54 (1.06)
50 (1.0)
34 (1.04)
45 (1.07)
0
[
d]
4
[
d]
5
[
e]
6
7
8
[f]
[
g]
9
1
0
1
2
3
0
1
1
1
2.5
2.5
2.5
36 (0.8)
33 (1.0)
10 (2.40)
Ce
Gd
0
[
a] The ester and cyclohexanone in THF (5 mL) were added to mischmetall/SmI
at 20 °C. [b] Ln (1.4 equiv.), SmI
mol-% according to substrate (cinnamyl acetate or cyclohexanone) in the lesser quantity. [d] Substrates were added over 9 h. [e] Substrates
were added over 1 h, and then stirring was continued for a further 1 h. [f] With PPh (30 mol-%). [g] Without SmI
2
/Pd over 3 h, and stirring was then continued for 12 h
2
(0.17 equiv.) according to substrate (cinnamyl acetate or cyclohexanone) in the lesser quantity. [c] In
3
2
.
Eur. J. Org. Chem. 2005, 4715–4722
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S. Médégan, F. Hélion, J.-L. Namy
FULL PAPER
Scheme 4.
nificantly (1.12 and 2.44), which could be indicative of the Table 3. Homoallylic alcohols were produced in moderate
0
involvement of different organometallic species.
yields, as with the SmI /Pd cat. system. Allyl phosphate
2
As the main components of mischmetall are cerium and gave the best results.
lanthanum, these were tested instead of mischmetall under
The coupling of a variety of ketones with cinnamyl esters
similar experimental conditions. In addition we used gado- was also studied (Table 4).
linium, an element that follows samarium in the lanthanide
group (Table 2, Entries 11–13).
With these esters, similar yields of homoallylic alcohols
were obtained which were, on the whole, satisfactory. In
With cerium and lanthanum, the expected homoallylic all these cases, mixtures of two homoallylic alcohols
alcohols were obtained in moderate yields (lower than those were obtained. The A/B ratios depend on the esters and
obtained with mischmetall), the A/B ratios being close to 1, ketones. Linear alcohols predominate, except with 4-non-
0
as with the alloy, whereas gadolinium gave the products in anone. In the absence of Pd , the allylation of cyclo-
low yields (10%) with an A/B ratio of 2.40. In the latter hexanone with cinnamyl phosphate occurred but the
case the formation of alcohols could mainly be ascribed to alcohols were produced in poor yields (25% instead of 63%
a stoichiometric reaction with samarium diiodide.
with palladium).
0
The mischmetall/[SmI /Pd
] system was also used
cat.Ј cat.
By considering the results and interpretations suggested
2
to allylate ketones and aldehydes with allyl esters (acetate, above (Scheme 2 and Figure 2), the following catalytic
carbonate and phosphate) under the optimised experimen- scheme III can be proposed for the reactions mediated by
0
tal conditions (Table 2, Entry 2). The results are collected in the mischmetall/[SmI /Pd
]
system (Figure 3).
2
cat.Ј cat.
Table 3. Allylation of ketones with allyl esters.[a]
1
R , R2
Entry
Product: isolated yield (%)
Y = –OCOCH
3
Y = –OPO(OC
2
H
5
)
2
2 3
Y = –OC(O) CH
1
2
3
4
5
6
–(CH
4-tBu-cyclohexanone
2
)
5
–
43
47[
36
43
26
47
46
45
46
60
34
34
40
18
52
23
b]
[b]
[b]
CH
n-C
CH
3
, n-C
6
H
4
13
H
4
H
9
, n-C
9
3
, PhCH
Ph, H
2
CH
2
complex mixture
complex mixture
[
a] SmI
to mischmetall/SmI
carbonate).
2
(0.17 equiv.), mischmetall (1.4 equiv.), Pd(PPh
3
)
4
(2.5 mol-%); ester (4 mmol) and ketone (4 mmol) in THF (5 mL) were added
0
2
/Pd over 3 h, and stirring was then continued at 20°C for 12 h. [b] OHax/OHeq = 2.7 (acetate); 2.5 (phosphate); 0.93
(
Table 4. Coupling of ketones with cinnamyl esters.[a]
1
R , R2
Entry
Isolated yields (%) A + B (A/B)
Y = –OCOCH
3
Y = –OPO(OC
2
H
5
)
2
2 3
Y = –OC(O) CH
1
2
3
4
5
–(CH
4-tBu-cyclohexanone
2
)
5
–
68 (1.12)
25 (1.8)
29 (1.6)
70 (0.36)
51 (1.4)
63 (1.83)
31 (1.26)
18 (1.35)
77 (0.58)
40 (1.18)
62 (1.26)
n.d.
19 (1.85)
73 (0.6)
54 (1.85)
CH
n-C
CH
3
H
, n-C
, n-C
, PhCH
6
H
4
13
H
4
9
9
3
2
CH
2
[
a] SmI
2
(0.17 equiv.), mischmetall (1.4 equiv.), Pd(PPh
3
)
4
(2.5 mol-%); ester (4 mmol) and ketone (4 mmol) in THF (5 mL) were added
0
to mischmetall/SmI
2
/Pd over 3 h, and stirring was then continued at 20°C for 12 h.
4718
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2005, 4715–4722

Reductive Coupling of Allylic Esters with Carbonyl Compounds
FULL PAPER
However, this mechanism seems unlikely since the A/B
ratios (linear/branched) obtained under stoichiometric
0
(
SmI /Pd cat.) conditions differ significantly to those ob-
2
tained under catalytic conditions (mischmetall/[SmI2/
0
Pd
]
), which probably indicates that it is not the or-
cat.Ј cat.
ganosamarium species that adds to the ketone under cata-
lytic conditions.
Presumably, the failure of the sequential procedure (for-
mation of a diene) results from an easy reaction between
an allylic lanthanide compound and a π-allylic complex of
palladium. Such couplings are well known in palladium
chemistry: “hard” nucleophiles first attack the palladium
atom to give a neutral complex which liberates the coupling
product through reductive elimination. This coupling re-
action also accounts for the moderate yields of alcohols ob-
tained with allyl esters.
Figure 3. Catalytic scheme III.
[
18]
It involves the formation of an allylic lanthanide com-
pound (Ln ϶ Sm), which adds to a carbonyl compound.
Since it has been shown that the organometallic species pre-
Since Yamamoto and co-workers have found that bis(π-
allyl)palladium complexes are able to react with electro-
[
19]
philes such as aldehydes and imines, we will consider the
possibility that such a species could be involved in reactions
pared by the reaction of cinnamyl bromide with the
mischmetall/SmI2,cat. system is stable,[13] it is somewhat sur-
0
0
mediated by the Ln/[SmI /Pd
]
or SmI /Pd
sys-
2
cat.Ј cat.
2
cat.
prising that a sequential procedure could not be carried out
with cinnamyl esters and the mischmetall/[SmI /Pd
system (Scheme 4). An alternative catalytic scheme IV can
be proposed which supposes the addition of an allylic sa-
marium compound onto the carbonyl compound (Fig-
ure 4).
0
tems.
]
2
cat.Ј cat.
To gain further information regarding this possibility, we
first prepared an organolanthanide compound from cinna-
[
13]
myl bromide
and then studied its reaction with cyclo-
hexanone in the presence of catalytic amounts of PdCl and
2
II
triphenylphosphane. Since Sm derivatives are also present
during this second step, reduction to Pd species is likely.
0
The results and experimental conditions are given in
Table 5.
The following comments can be made: (1) the addition
of the organometallic species to cyclohexanone is slow with
several hours needed to reach completion, (2) the presence
of palladium complexes has a significant effect on the yields
of the alcohols, and (3) the beneficial effect is moderate and
the A/B ratios do not vary in the presence or absence of
palladium complexes.
This means that palladium complexes are involved in se-
veral steps of the reactions (the formation of organometal-
Figure 4. Catalytic scheme IV.
Table 5. Addition of cinnamyllanthanide compounds to cyclohexanone in the presence of palladium complexes.
Entry
(PdCl
2
+ 4 PPh
3
) [mol-%]
Reaction time [h]
Isolated yield [%] A + B (A/B)
1
2
3
4
0
2.5
0
0.5
0.5
1.5
1.5
16 (0.88)
27 (0.84)
52 (0.96)
80 (0.95)
2.5
Eur. J. Org. Chem. 2005, 4715–4722
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S. Médégan, F. Hélion, J.-L. Namy
FULL PAPER
Table 6. Dependence of A/B ratios on reaction conditions.
Entry
Reducing system
Y
A/B
1
2
4
4
5
6
7
8
9
SmI
SmI
SmI
SmI
2
2
2
2
–OCOCH
–OPO(OC
–OC(O) CH
–Br
–OCOCH
–OPO(OC
–OC(O) CH
–Br
–OCOCH
–OPO(OC
–OC(O) CH
–Br
–OCOCH
–OPO(OC
–OC(O) CH
–Br
3
n.r.
2.24
2.65
2.76
2.44
2.40
2.80
2.85
n.r.
2
H
5
)
3
2
2
2
2
2
0
SmI
SmI
SmI
SmI
2
2
2
2
/Pd cat.
/Pd cat.
/Pd cat.
/Pd cat.
3
0
2 5
H )
0
2
3
0
mischmetall/SmI2,cat.
mischmetall/SmI2,cat.
mischmetall/SmI2,cat.
3
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
2
H
5
)
3
0.96
n.r.
2
mischmetall/SmI2,cat.
0.96
1.12
1.83
1.26
0.95
0.8
0
mischmetall/[SmI
mischmetall/[SmI
mischmetall/[SmI
mischmetall/[SmI
2
2
2
2
/Pd cat.Ј
]
cat.
]
cat.
]
cat.
]
cat.
3
0
/Pd cat.Ј
2 5
H )
0
/Pd cat.Ј
2
3
0
/Pd cat.Ј
0
La/[SmI
Ce/[SmI
2
/Pd cat.Ј
]
]
cat.
–OCOCH
–OCOCH
3
0
2
/Pd cat.Ј
cat.
3
1.0
lics from allylic esters and the reactions of these species with
In previous reports,[21,22] α-adducts (isomer A), in which
electrophiles). However, the addition to carbonyl com- the allylic group is linked through the less hindered posi-
pounds probably does not proceed through a bis(π-allyl)- tion, are considered to form through the reaction of orga-
3
palladium species.
nometallic species possessing an η -allyl moiety. In con-
In the reactions involving cinnamyl esters, homoallylic trast, γ-adducts (isomer B), in which the allyllic group is
alcohols were obtained as mixtures of linear (A) and attached through the more highly substituted position, re-
branched (B) isomers. The A/B ratio varies widely accord- sult from the reaction of an organometallic species with an
1
ing to the substrates and reducing systems used. The results η -allyl structure (Scheme 6).
obtained from the reactions with cyclohexanone are col-
lected in Table 6; those concerning cinnamyl bromide and
this ketone have been included for an exhaustive compari-
son (Table 6).
The A/B ratios are between 2.24 and 2.85 when samar-
ium diiodide is used in stoichiometric amounts, whereas
they are in the range of 0.8–1.26 when samarium diiodide
is used in catalytic amounts with mischmetall, lanthanum
or cerium as co-reductants (with the exception of cinnamyl
Scheme 6.
phosphate, Entry 14). In the first case it is likely that an
organosamarium compound is formed, which adds to the
ketone; in the second case, homoallylic alcohols should re-
sult from the reaction of an organolanthanum and/or an
organocerium compound. This feature is also observed in
the reactions of 2-octanone (Table 1, Entry 4; Table 4, En-
On the basis of this assumption, it could be considered
that cinnamylsamarium compounds possess an η -allyl
3
moiety whilst cinnamyllanthanum and -cerium compounds
1
could mainly have an η -allyl structure. This result some-
what conflicts with recent results concerning crotyl Grig-
[
20]
try 4; ref. and Scheme 5).
[23]
nard reagent/LnCl systems. However, other factors such
3
as steric hindrance (organometallic, electrophile) could also
affect the product distribution. Besides, comparison with
the reactivity of organolanthanides prepared by another
procedure is inconclusive.
Conclusions
To conclude, we have studied some new reactions of al-
0
Scheme 5.
720
lylic esters with the SmI /Pd
system and we have dem-
2
cat.
4
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Reductive Coupling of Allylic Esters with Carbonyl Compounds
FULL PAPER
onstrated that it is possible to use the mischmetall/[SmI / with SmI
2
(0.7 mmol) in a Schlenk tube under argon at room tem-
perature. A solution of an allylic compound (4 mmol) and ketone
4 mmol) in THF (7 mL) was slowly added to the THF/SmI /
2
2
0
Pd
]
system to mediate the allylation of carbonyl
cat.Ј cat.
(
compounds with allylic esters. Thus a “two-stage catalysis”
was carried out using a cheap alloy of the light lanthanides
as a co-reductant. Several experimental facts remain to be
explained, especially the product distribution of the homo-
allylic alcohols.
mischmetall suspension over 3 h. The mixture was then stirred for
an additional period of 12 h, diluted with diethyl ether, quenched
with HCl (1 ) and stirred for 15 min to obtain a clear solution,
which was extracted with diethyl ether. The combined extracts were
washed with brine, sodium thiosulfate and brine again. The organic
4
layer was dried with MgSO and the solvents were removed under
reduced pressure. The crude material was purified by flash
Experimental Section
General: 1H and 13C NMR spectra were recorded at 250 and
chromatography on silica gel.
0
Reaction Procedure Using Ln/[SmI /Pd
nide powder (Ln = mischmetall, La, Ce or Gd, 5 mmol), tetrakis-
2
cat.Ј cat.
Systems: Lantha-
]
63 MHz, respectively, with a Bruker AC 250 instrument (unless
(
(
triphenylphosphane)palladium (115 g, 0.1 mmol) and SmI
0.7 mmol) were stirred in THF (7 mL), in a Schlenk tube under
2
otherwise stated). IR spectra were recorded with an FTIR IFS 66
Bruker spectrometer. MS data were determined with a GC/MS Fi-
son 8000 instrument. EI was performed at 70 eV. HRMS data and
electrospray mass spectra were recorded with a GC/MS Finningan-
MAT-95-S spectrometer. Flash chromatography was performed on
silica gel (Merck 230–240 mesh; 0.0040–0.0630 mm). All the com-
pounds (homoallylic alcohols and dienes), which were obtained in
the reactions indicated above, were identified by comparison with
previously published spectroscopic data. All commercially available
organic compounds were distilled before use. Lanthanide metals
argon at room temperature for 5 min. A solution of an allylic com-
pound (4 mmol) and ketone (4 mmol) in THF (7 mL) was slowly
added to the THF/SmI
h. The mixture was then stirred for an additional period of 12 h,
diluted with diethyl ether, quenched with HCl (1 ) and stirred for
5 min to obtain a clear solution, which was extracted with diethyl
ether. The combined extracts were washed with brine, sodium thio-
sulfate and brine again. The organic layer was dried with MgSO
2 3 4
/Pd[P(Ph) ] /lanthanide suspension over
3
1
4
and the solvents were removed under reduced pressure. The crude
material was purified by flash chromatography on silica gel.
(
(
ingots) were purchased from the Acros Company and mischmetall
cerium mixed metal) from Fluka (about $60 per 500 g). Mischmet-
all ingots (about 5 g) were easily powdered in air with a rasp (CAU-
TION! Mischmetall powder is pyrophoric, the ingot may give out
sparks when it is scraped, powder must be collected in a flask filled
with argon). The powder was kept under argon in a Schlenk tube,
the average molecular weight of mischmetall is 140. Tetra-
hydrofuran (THF) was distilled under argon from sodium benzo-
phenone ketyl. Samarium diiodide was prepared as described pre-
/Pd0cat.Ј
Sequential Procedure Using the Mischmetall/[SmI
2
]cat. Sys-
tem: Mischmetall powder (0.7 g, 5 mmol), tetrakis(triphenylphos-
phane)palladium (115 g, 0.1 mmol) and SmI (0.7 mmol) were
stirred in THF (7 mL) in a Schlenk tube under argon at room tem-
perature for 5 min. A solution of an allylic compound (4 mmol)
2
2 3 4
in THF (7 mL) was slowly added to the THF/SmI /Pd[P(Ph) ] /
mischmetall suspension over 3 h. A solution of a ketone (4 mmol)
in THF (5 mL) was then quickly added. The mixture was then
stirred for an additional period of 12 h, diluted with diethyl ether,
quenched with HCl (1 ) and stirred for 15 min to obtain a clear
solution, which was extracted with diethyl ether. The combined ex-
tracts were washed with brine, sodium thiosulfate and brine again.
The organic layer was dried with MgSO , and the solvents were
4
removed under reduced pressure. The crude material was purified
by flash chromatography on silica gel.
[
20]
viously. Allylic carbonates were prepared according to the pro-
[
24]
cedure of Trost et al.; allylic phosphates were prepared using the
[
25]
same procedure.
All reactions were carried out under argon in
Schlenk tubes using standard vacuum-line techniques.
Reaction Procedure Using SmI : A solution of allylic compound
2 mmol) and ketone (2 mmol) in THF (7 mL) was slowly added
2
(
2
to a solution of SmI (4.4 mmol) in THF (44 mL) in a Schlenk
tube under argon at room temperature over 3 h. The mixture was
then stirred for an additional period of 12 h, diluted with diethyl
ether, quenched with HCl (1 ) and stirred for 15 min to obtain a
clear solution, which was extracted with diethyl ether. The com-
bined extracts were washed with brine, sodium thiosulfate and
brine again. The organic layer was dried with MgSO and the sol-
4
vents were removed under reduced pressure. The crude material
was purified by flash chromatography on silica gel.
Preparation of Cinnamyllanthanide Compounds and Addition to Cy-
clohexanone in the Presence of PdCl
2
/PPh
0.7 g, 5 mmol) was suspended in THF (7 mL) with SmI
0.7 mmol) in a Schlenk tube under argon at room temperature. A
3
: Mischmetall powder
(
(
2
solution of cinnamyl bromide (702 mg, 4 mmol) in THF (7 mL)
was slowly added to the THF/SmI /mischmetall suspension over
h. Palladium chloride (17.7 mg, 0.1 mmol) suspended in THF
2
3
/Pd0cat. System: Tetrakis(tri-
(7 mL) with triphenylphosphane (105 mg, 0.4 mmol) and cyclo-
hexanone (392 mg, 4 mmol) was then quickly added. The mixture
was then stirred for an additional period of 0.5 or 1.5 h, diluted
with diethyl ether, quenched with HCl (1 ) and stirred for 15 min
to obtain a clear solution, which was extracted with diethyl ether.
The combined extracts were washed with brine, sodium thiosulfate
and brine again. The organic layer was dried with MgSO and the
4
solvents were removed under reduced pressure. The crude material
was purified by flash chromatography on silica gel.
Reaction Procedure Using the SmI
phenylphosphane)palladium (23.4 g, 0.02 mmol) was suspended in
THF (44 mL) with SmI (4.4 mmol) in a Schlenk tube under argon
at room temperature for 5 min. A solution of an allylic compound
2 mmol) and ketone (2 mmol) in THF (7 mL) was then slowly
added to the THF/SmI /Pd(PPh suspension over 3 h. This mix-
2
2
(
2
3 4
)
ture was stirred for an additional period of 12 h, diluted with di-
ethyl ether, quenched with HCl (1 ) and stirred for 15 min to ob-
tain a clear solution, which was extracted with diethyl ether. The
combined extracts were washed with brine, sodium thiosulfate and
4
brine again. The organic layer was dried with MgSO and the sol-
vents were removed under reduced pressure. The crude material
was purified by flash chromatography on silica gel.
Acknowledgments
We are indebted to Professor J. C. Fiaud for fruitful discussions. We
Reaction Procedure Using the Mischmetall/SmI2,cat. System: thank the University of Paris-Sud and the CNRS for their financial
Mischmetall powder (0.7 g, 5 mmol) was suspended in THF (7 mL) support.
Eur. J. Org. Chem. 2005, 4715–4722
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4721

S. Médégan, F. Hélion, J.-L. Namy
FULL PAPER
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Received: April 26, 2005
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4722
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2005, 4715–4722