One-pot β-alkylation of secondary alcohols with primary alcohols catalyzed by ruthenacycles

Article abstract of DOI:10.1016/j.tetlet.2012.01.025

A ruthenacycle-catalyzed one-pot β-alkylation of secondary alcohols with primary alcohols is described. A survey of four C-N chelate ruthenacycles synthesized via the cyclometallation reaction of phenylmethanamine, N-methylphenylmethanamine, N,N-dimethylphenylmethanamine, and naphthalen-1-ylmethanamine with [(η⁶-C₆H ₆)RuCl₂]₂ was undertaken. All four complexes were found to be active with the phenylmethanamine-based ruthenacycle showing the best combination of reactivity and product selectivity among the four. An expanded scope of substrates was also studied with the inclusion of unsaturated primary alcohols. The reactivity trend observed gave insights into the role of hydrogen bonding in the catalytic mechanism involving transfer hydrogenation between the substrates and the transition metal catalyst.

Full text of DOI:10.1016/j.tetlet.2012.01.025

Tetrahedron Letters 53 (2012) 1450–1455
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
One-pot b-alkylation of secondary alcohols with primary alcohols catalyzed by
ruthenacycles
⇑
Xu Chang, Low Wei Chuan, Li Yongxin, Sumod A. Pullarkat
Division of Chemistry & Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
a r t i c l e i n f o
a b s t r a c t
Article history:
A ruthenacycle-catalyzed one-pot b-alkylation of secondary alcohols with primary alcohols is described.
A survey of four C–N chelate ruthenacycles synthesized via the cyclometallation reaction of phenylme-
thanamine, N-methylphenylmethanamine, N,N-dimethylphenylmethanamine, and naphthalen-1-ylme-
Received 13 October 2011
Revised 17 December 2011
Accepted 6 January 2012
Available online 14 January 2012
thanamine with [(g
6-C6H6)RuCl2]2 was undertaken. All four complexes were found to be active with
the phenylmethanamine-based ruthenacycle showing the best combination of reactivity and product
selectivity among the four. An expanded scope of substrates was also studied with the inclusion of unsat-
urated primary alcohols. The reactivity trend observed gave insights into the role of hydrogen bonding in
the catalytic mechanism involving transfer hydrogenation between the substrates and the transition
metal catalyst.
Keywords:
b-Alkylation
Homogeneous catalysis
Transfer hydrogenation
Ruthenacycle
Ó 2012 Elsevier Ltd. All rights reserved.
Catalytic one-pot b-alkylation, a facile tandem protocol giving
b-alkylated secondary alcohols as the products and water as a
by-product, has attracted interest in recent years.1 When com-
pared to traditional protocols, catalytic one-pot b-alkylation has
positioned itself as a ‘green’ process in terms of atom economy,
avoidance of protecting groups, and waste minimization.1,2 Alkyl-
ation of secondary alcohols with primary alcohols typically in-
volves dehydrogenation of the alcohols to an aldehyde or ketone,
aldol coupling, loss of water, and subsequent hydrogenation of
the resulting enone to yield the coupled alcohol.1g Another possible
product of this procedure is the alkylated ketone.
Within the family of organotransition metal catalysts, metalla-
cycles have been intensively investigated due to their promising
catalytic ability in a wide array of organic synthetic protocols.3
We have studied the application of palladacycles in asymmetric
catalysis involving C–C and P–C bond formations.4 Ruthenacycles
have attracted attention for the synthesis of a range of valuable
catalysts, anti-cancer drugs, and electron shuttles.5 However, the
most widely studied organic transformations catalyzed by ruthe-
nacycles are limited to C–C or C–X (X = heteroatom) bond forma-
tion, hydrogenation, dehydrogenation, hydrogen transfer, and
racemisation reactions.5e,6 In particular, ruthenium-promoted
homogenous hydrogenation catalysis has been known for almost
40 years.6a In spite of their reputation in promoting the aforemen-
tioned reactions and their unique redox characteristics, the poten-
tial of ruthenacycles acting as both an oxidant and reductant in a
one-pot multi-step b-alkylation reaction has remained unexplored.
Iridium-based catalysts dominate the scene in one-pot, multi-
step b-alkylation reactions.1b,d,g,h We ourselves have reported a
low catalyst loading iridium-thioether-dithiolate catalyst for this
reaction.1h The search for alternatives has led to the development
of ruthenium-based catalysts incorporating N-heterocyclic carb-
enes (NHCs),7 phosphines, and terpyridine ligands.8 Interestingly,
the NHC ligand system developed by Crabtree is highly effective
when used with iridium but gave very poor conversions when used
in conjunction with ruthenium.7 Despite their proven potential in
hydrogen transfer scenarios, there are no literature reports on
the application of ruthenacycles to allow selective formation of
alkylated secondary alcohols in a one-pot process.
In this Letter, we report the evaluation of a series of ruthenacy-
cles bearing C–N chelate ligands, which show potential as catalysts
for the b-alkylation of a wide range of substrates including unsat-
urated primary alcohols. The insights obtained from this study on
catalyst design should help in the further development of
other cheaper transition metal systems as an alternative to the
iridium-based complexes that currently dominate this catalytic
protocol.
Treatment of phenylmethanamine, N-methylphenylmethan-
amine, and N,N-dimethylphenylmethanamine with 0.5 equiv of
[(g
6-C6H6)RuCl2]2 in the presence of 1 equiv of NaOH and 1 equiv
of KPF6 led to the formation of ruthenacycles 4–6 (Scheme 1) in
good yields.9 As far as we know, the solid state structures of 4
and 5 have not been reported and therefore crystals suitable for
single crystal X-ray diffraction studies were obtained by the slow
diffusion of diethyl ether into acetonitrile.10
The molecular characteristics of 4 and 5, as shown in Figures 1
⇑
Corresponding author. Tel.: +65 6316 8906; fax: +65 6316 6984.
E-mail address: sumod@ntu.edu.sg (S.A. Pullarkat).
and 2, where in accordance with those previously reported for 611
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2012.01.025

X. Chang et al. / Tetrahedron Letters 53 (2012) 1450–1455
1451
+
NR1R2
CH3CN, NaOH
NCCH3
NR1R2
Cl
Cl
Cl
-
+
Ru
PF6
Ru
Ru
KPF6, 45 °C, Ar
Cl
1 R1 = R2 = H
2 R1 = H, R2 = Me
3 R1 = R2 = Me
4 R1 = R2 = H (48%)
5 R1 = H, R2 = Me (65%)
6 R1 = R2 = Me (72%)
Scheme 1. Synthesis of the cycloruthenated compounds 4–6.
It is well established that besides tuning the substituents on the
N donor, altering the organic ligand attached to the metal atom can
also modify drastically the activity, selectivity, and stability of
transition metal catalysts.13 We therefore proceeded to synthesize
complex 7 with the aim of evaluating a series of complexes which
could provide insights into catalyst design. The reaction of naph-
thalen-1-ylmethanamine with [(g
6-C6H6)RuCl2]2 led to the forma-
tion of ruthenacycle 7 in good yield (Scheme 2).
The characteristic downfield chemical signal (d = 8.04) of the
aromatic proton ortho to the Ru–C bond as well as the presence
of a downfield chemical shift (d = 164.20) attributed to the highly
de-shielded Ru-bound carbon indicated that the desired complex
7 had been synthesized successfully.14 With the four ruthenacycles
4–7 in hand we proceeded to analyze their catalytic potential in
the b-alkylation reaction.
The most accepted mechanism for the one-pot b-alkylation of
secondary alcohols with primary alcohols involves dehydrogena-
tion of the alcohol to an aldehyde or ketone, aldol coupling, loss
of water, and subsequent hydrogenation of the resulting enone to
yield the coupled alcohol (Scheme 3).1g
Figure 1. ORTEP representation of the cation of 4 with ellipsoids shown at 50%
thermal probability. Selected hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (°): Ru(1)-N(2) 2.055(2), Ru(1)-C(1) 2.067(2), Ru(1)-N(1)
2.139(2), N(2)-Ru(1)-C(1) 86.14(8), N(2)-Ru(1)-N(1) 87.57(8), C(1)-Ru(1)-N(1)
77.16(9).
Ruthenacycles have been previously employed as catalysts for
the transfer hydrogenation of carbonyl compounds.5e Among
these, particular attention has been devoted to a catalyst which
incorporates an amine in the metallacycle ring.9a,b,13,15 In the
absence of acidic NH protons, it is generally assumed that Ru-
catalyzed transfer hydrogenation occurs via metal hydride and
alkoxide species through an inner-sphere mechanism.15b An
outer-sphere mechanism, involving a Ru–H hydride and N–H
proton has also been proposed.15b,16 Both mechanisms involve
two parallel reactions that can transfer hydrogen between the
carbonyl compounds and alcohols. It was therefore rational for
us to test the catalytic potential of the ruthenacycles since the
current one-pot b-alkylation protocol involves a similar transfer
hydrogenation scenario.
We started our catalytic screening using equimolar amounts of
benzyl alcohol and 1-phenylethanol with the aim of evaluating the
feasibility of the catalytic system and to ascertain the optimum
conditions (Table 1). In a typical reaction, a mixture of 1-phenyl-
ethanol (1.0 mmol) and benzyl alcohol (1.0 mmol) was dissolved
in toluene (0.3 mL) in the presence of NaOtBu (1.0 mmol) and cat-
alyst (1.0 mol %), and allowed to react at 110 °C for 17 h. The high-
est conversions for the alcohol were obtained using complex 4 as
the catalyst (entries 1, 6, and 7, Table 1). When the amount of base
was reduced to 0.5 mmol (entries 2, 9, 11 and 13, Table 1) the
selectivity for the alcohol product was lowered. Likewise, lowering
the catalyst loading also had a detrimental impact on the selectiv-
ity, but not on the reactivity (entry 3, Table 1). The reaction time
had a considerable influence on the selectivity of the process. It
was consistently observed for the four catalysts, allowing the reac-
tion to proceed for an extended period of time (48 h) favored the
formation of the ketone co-product via dehydrogenation of the
alcohol. A similar decrease in alcohol formation was also evident
at higher temperatures. With shorter reaction time, higher
Figure 2. ORTEP representation of the cation of 5 with ellipsoids shown at 50%
thermal probability. Selected hydrogen atoms are omitted for clarity. Selected bond
lengths [Å] and bond angles [°]: Ru(1)-N(2) 2.0436(14), Ru(1)-C(1) 2.0598(14),
Ru(1)-N(1) 2.1600(13), N(2)-Ru(1)-C(1) 86.09(6), N(2)-Ru(1)-N(1) 84.19(5), C(1)-
Ru(1)-N(1) 78.06(5).
and other ruthenacycles.12 We observed that the presence of
methyl substituents on the nitrogen in complexes 4–6 resulted in
extended Ru–N bond lengths [2.139(2), 2.1600(13), 2.170(2) Å,11
respectively]. Although from an electronic viewpoint, the presence
of a methyl substituent on the nitrogen should increase its nucle-
ophilicity resulting in stronger Ru–N bonds, the steric effect over-
shadows the electronic effect in the context of the constricted
environment enveloping the ruthenium center.

1452
X. Chang et al. / Tetrahedron Letters 53 (2012) 1450–1455
+
2
NCCH3
NH2
NH2
1
Ru
-
CH3CN, NaOH
Cl
PF6
Cl
Cl
+
Ru
Ru
KPF6, 45 °C, Ar
Cl
7 (40%)
Scheme 2. Synthesis of the cycloruthenated compound 7.
In view of the results from the catalyst screening studies, we
proceeded to study the scope and limitations of catalyst 4 using
a wide assortment of secondary alcohols and primary alcohols un-
der the optimized conditions (Table 2). Generally, we observed that
catalyst 4 was able to activate the efficient transformations of
many primary and secondary alcohols into the targeted alkylated
alcohols. The reactions of 1-phenylethanol or 1-(4-methoxy-
phenyl)ethanol with various benzyl alcohols containing an elec-
tron-donating or an electron-withdrawing group proceeded with
excellent conversion (90–98%) and good to excellent selectivity
for the alcohol products (entries 1a–d and 2a–d, Table 2). These
values are comparable to those obtained for the reported irid-
ium-based catalyst systems, although they show much better
reactivity.1,2
A closer examination revealed that varying the substituent on
1-phenylethanol did not have any impact on the product conver-
sion and selectivity on reaction with benzyl alcohol (entries 1a,
2a, and 3a, Table 2). Interestingly, unsaturated primary alcohols
and aromatic secondary alcohols (entries 1e, 1f, and 2e, Table 2)
also gave moderate yields of alkylated alcohols and ketones. The
results from the alkylation of such unsaturated alcohol substrates
are conspicuously rare in literature reports involving both Ir and
Ru catalysts. Aromatic primary alcohols and aromatic secondary
alcohols gave better conversions compared to aromatic primary
alcohols with aliphatic secondary alcohols (entries 4 and 5, Table 2)
and aliphatic primary alcohols with aromatic secondary alcohols
(entries 1g, 2f and 3b, Table 2). It is seen from literature reports
that aliphatic alcohols do not usually result in good conversions
for this coupling reaction.1
O
OH
OH
[cat.]
R
OH
or / +
Ar
R
Ar
R
Ar
Hydrogen
elimination
Hydrogenation
O
O
O
aldol condensation
- H2O
Ar
R
H
R
Ar
Scheme 3. Generally accepted catalytic cycle of b-alkylation of secondary alcohol
with primary alcohol.
selectivity in favor of the alcohol product was observed, but the
overall product conversion deteriorated (entry 7, Table 1). Lower-
ing the temperature from 110 to 90 °C resulted in an appreciable
decrease in the product conversion with catalyst 4 (entry 6,
Table 1). The use of a less basic additive, NaOH, also resulted in a
lower selectivity (entry 4, Table 1) while the use of Na2CO3 gave
no product (entry 5, Table 1). Overall under the various conditions
tested, ruthenacycles 5, 6, and 7 exhibited lower activity and/or
product selectivity when compared to 4.
These results indicated that complex 6, without an NH moiety,
could still generate the product in high yields. However when com-
pared with 5 and 6, complexes 4 and 7 (with the NH2 group on the
metallacycle) gave better results thus indicating the possibility
that the NH functionality plays a role in enhancing the reaction
yield. Noyori had reported a similar enhancement of reactivity by
N–H moieties in transfer hydrogenations.6a,16
Table 1
Screening of catalysts and optimization of the reaction conditionsa,17
OH
OH
O
[cat.], base (100 mol%)
110 °C, toluene, 17 h
+
+
Ph
OH
Ph
Ph
Ph
Ph
Ph
Entry
Catalyst (mol%)
Base (mol %)
Conversion (%)
Alcohol–ketone
1
2
3
4
5
4 (1.0)
4 (1.0)
4 (0.5)
4 (1.0)
4 (1.0)
4 (1.0)
4 (1.0)
5 (1.0)
5 (1.0)
6 (1.0)
6 (1.0)
7 (1.0)
7 (1.0)
NaOtBu (100)
NaOtBu (50)
NaOtBu (100)
NaOH (100)
Na2CO3 (100)
NaOtBu (100)
NaOtBu (100)
NaOtBu (100)
NaOtBu (50)
NaOtBu (100)
NaOtBu (50)
NaOtBu (100)
NaOtBu (50)
96
75
97
99
0
82
60
96
99
84
96
99
99
97:3
78:22
58:42
66:34
0
93:7
99:1
76:24
63:37
96:4
76:24
50:50
67:33
6b
7c
8
9
10
11
12
13
a
Reaction conditions: 1 mmol of 1-phenylethanol, 1 mmol of benzyl alcohol, catalyst, base, 0.3 mL of toluene, 110 °C, 17 h. Conversions (based on the secondary alcohol)
and ratios in Table 1 were determined by 1H NMR spectroscopy.
b
Reaction conducted at 90 °C.
Reaction time of 9 h.
c

X. Chang et al. / Tetrahedron Letters 53 (2012) 1450–1455
1453
Table 2
b-Alkylation of secondary alcohols with primary alcoholsa,17
Entry
Secondary alcohol
Primary alcohol
Conversion (%)
Alcohol–Ketone
OH
R2
OH
R1
1a
1b
1c
1d
1e
1f
1g
2a
2b
2c
2d
2e
2f
R1 = Ph
R2 = Ph
96
90
94
98
67
44
40
93
94
92
95
44
51
92
70
85
97:3
75:25
96:4
R1 = Ph
R2 = 3-ClC6H4
R2 = 4-ClC6H4
R2 = 4-MeOC6H4
R2 = C6H5CH@CH
R2 = CH2@CH
R2 = n-Bu
R
R
R
R
R
R
R
1 = Ph
1 = Ph
62:38
70:30
38:62
80:20
90:10
60:40
85:15
55:45
34:66
75:25
98:2
1 = Ph
1 = Ph
1 = Ph
1 = 4-MeOC6H4
1 = 4-MeOC6H4
R2 = Ph
R2 = 3-ClC6H4
R2 = 4-ClC6H4
R2 = 4-MeOC6H4
R2 = CH2@CH
R2 = n-Bu
R1 = 4-MeOC6H4
R
R
R
R
R
R
1 = 4-MeOC6H4
1 = 4-MeOC6H4
1 = 4-MeOC6H4
1 = 4-ClC6H4
1 = 4-ClC6H4
1 = CH3
3a
3b
4
R2 = Ph
R2 = n-Bu
96:4
36:64
R2 = Ph
OH
5
R2 = Ph
90
40:60
a
Reaction conditions: 1 mmol of 1-phenylethanol, 1 mmol of benzyl alcohol, 1 mmol of NaOtBu, 1 mol % 4, 0.3 mL of toluene, 110 °C, 17 h. Conversions (based on the
secondary alcohol) and ratios were determined by 1H NMR spectroscopy.
H
O
H
O
R'
R
R'
R
R'
O
R
Ru
Ru
Ru
H
Ru
O
+
H
H
N
N
H
R
N
H
R
R'
R
N
H
H
H
O
O
H
H
H
[Ru]-H
[Ru]
O
O
R2
+
[Ru]
R1
ß-hydrogen
elimination
ONa
O
O
+
R2
ONa
+
R1
R1
R2
H
[Ru]
[Ru]-H
Cross-aldol
condensation
Base
OH
O
O
+
R1
R2
R1
R2
Scheme 4. Proposed catalytic cycle.
R1
R2
When considering the catalytic cycle for the b-alkylation reac-
tion involving ‘hydrogen borrowing’, an important intermediate
is the metal hydride species.1 In our context, the Ru–H species is
already an 18 electron entity and this precludes the coordination
of the substrate to the Ru center. Thus the enhanced conversions
seen for aromatic alcohols could be rationalized by two explana-
ing the hydrogen transfer during the catalytic cycle resulting in
excellent conversions. Secondly, alkyl alcohols will form a less
electrophilic aldehyde species when undergoing the catalytic pro-
cess rendering them less susceptible to attack by the nucleophile
thus resulting in diminished conversions. Additionally, alkyl alco-
hols lack the postulated CH/ attractions for improved interac-
p
tions. Firstly, CH/
charge-transfer interactions exist between the
of the catalyst and the phenyl moiety of the substrate resulting
in enhanced interactions when both are brought together in closer
proximity during the catalytic cycle. Thereby it is postulated that
with such improved interactions it will be more efficient in assist-
p
attractions based on both electrostatic and
tions. Evidently, complex 4 is an efficient catalyst for this
g
6-benzene ligand
coupling reaction giving excellent conversions for most substrates.
The formation of the Ru–H species is also facilitated by the ten-
dency of the intermediate ruthenium alkoxides to undergo thermal
decomposition to metal hydrides.15 Simultaneously, both alcohols
are subjected to the dynamic ruthenium-catalyzed redox shuttle to

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X. Chang et al. / Tetrahedron Letters 53 (2012) 1450–1455
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form the b-unsaturated ketone (Scheme 4). Together with the suc-
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the aforementioned CH/p attractions do not affect the catalytic
cycle.
Our catalytic studies employing various ruthenacycles have
provided preliminary insights as to why complex 4 has overall
superior reactivity for the b-alkylation process over the other ana-
logues tested in this study. For the catalytic scenario (Scheme 4),
taking into consideration the fact that catalyst 6 possesses no pro-
ton on the amino nitrogen and in light of the experimental evi-
dence of Baratta and co-workers that the coordinated primary
amine in ruthenacycles displays relatively weak acidity,15b we pro-
pose an alternative mechanism as shown in Scheme 4.
The presence of a hydrogen bond therefore greatly assists the
hydrogen transfer process to generate a ruthenacycle-hydride spe-
cies as shown in Scheme 4, thus enhancing the reactivity of com-
plexes 4 and 7 compared to 5 and 6. A detailed mechanistic
investigation to further understand the role of the amine hydrogen
in such hydrogen transfer protocols is currently underway in our
laboratory.
11. Le Lagadec, R.; Rubio, L.; Alexandrova, L.; Toscano, R. A.; Ivanova, E. V.; Meskys,
R.; Laurinavicius, V.; Pfeffer, M.; Ryabov, A. D. J. Organomet. Chem. 2004, 689,
4820–4832.
In conclusion, we have shown that ruthenacycles, prepared eas-
ily in a single step from benzylamines, have good potential as cat-
alysts in the one-pot b-alkylation of secondary alcohols with
primary alcohols. This is the first report of the use of a ruthenacycle
in this particular organic synthetic scenario and counts among the
few instances in the literature when non-iridium-based catalysts
have been employed successfully. Our catalyst and substrate
screening studies, besides expanding the reaction scope to unsatu-
rated primary alcohols, also revealed the importance of the amino
hydrogen in controlling the catalytic activity of the ruthenacycles
in such hydrogen transfer processes. Studies on further modifica-
tion of the catalyst topologies including generating chiral variants,
which can be tested in asymmetric synthetic scenarios, are cur-
rently underway in our laboratory.
12. (a) Yuan, M.-J.; Pullarkat, S. A.; Li, Y.; Lee, Z.-Y.; Leung, P. H. Organometallics
2010, 29, 3582–3588; (b) Liu, F.; Pullarkat, S. A.; Li, Y.; Chen, S.; Yuan, M.-J.; Lee,
Z.-Y.; Leung, P. H. Organometallics 2009, 28, 3941–3946; (c) Pullarkat, S. A.;
Cheow, Y. L.; Li, Y.; Leung, P. H. Eur. J. Inorg. Chem. 2009, 16, 2375–2382.
13. Jerphagnon, T.; Haak, R.; Berthiol, F.; Gayet, A. J. A.; Ritleng, V.; Holuigue, A.;
Pannetier, N.; Pfeffer, N.; Voelklin, A.; Lefort, L.; Verzijl, G.; Tarabiono, C.;
Janssen, D. B.; Minnaard, A. J.; Feringa, B. L.; Vries, J. G. Top. Catal. 2010, 53,
1002–1008.
14. Procedure for the preparation of [(
g
6-C6H6)Ru(C10H6-1-CH2NH2)CH3CN]+PFÀ6
(7): Naphthalen-1-ylmethanamine (157 mg, 1.0 mmol) was dissolved in MeCN
(5 mL) and benzene ruthenium(II) chloride dimer (276 mg, 0.5 mmol) was
added. Next, NaOH (40 mg, 1.0 mmol) and excess KPF6 (386 mg, 2.1 mmol)
were added. The mixture was left to stir for 4 h at 45 °C. The resulting
suspension was filtered, washed with hexane and dried under vacuum to
afford a yellowish brown solid. This solid was redissolved in MeCN, filtered
over neutral Al2O3, using MeCN as eluent. A yellow fraction was collected and
concentrated in vacuo. The resulting yellow residue was dissolved in
a
minimum of CH2Cl2 and upon adding few drops of hexene, yellow
a
a
precipitate was obtained (209 mg, 40% yield). Anal. Calcd for C19H19N2RuPF6: C,
43.7; H, 3.7; N, 5.4. Found: C, 43.2; H, 3.7; N, 5.3. 1H NMR (500 MHz, CD3CN):
d = 3.84 (br s, 1H, N–H), 4.09 (m, 1H, C–H), 4.55 (m, 1H, C–H), 5.22 (br s, 1H, N–
Acknowledgments
H), 5.63 (s, 6H,
(m, 2H, aromatics), 7.80 (d, 1H, JH–H = 7.20 Hz, aromatics), 8.04 (d, 1H, JH–
H = 8.15 Hz, C2). 13C{1H} NMR (125 MHz, CD3CN): d = 52.7 (CH2), 86.7 (g6
g
6-C6H6), 7.32 (m, 1H, aromatics), 7.39 (m, 1H, aromatics), 7.56
3 3
The authors acknowledge the support from the Nanyang Tech-
nological University and a research scholarship to X.C.
-
C6H6), 123.2, 123.4, 125.1, 125.6, 128.2, 128.7, 131.3, 137.9, 141.5, 164.2 (C1).
ESI+–MS: m/z 376.79 [M–PF6]+.
References and notes
15. (a) Matsumura, K.; Arai, N.; Hori, K.; Saito, T.; Sayo, N.; Ohluma, T. J. Am. Chem.
Soc. 2011, 133, 10696–10699; (b) Baratta, W.; Ballico, M.; Esposito, G.; Rigo, P.
Chem. Eur. J. 2008, 14, 5588–5595.
16. Yamakawa, M.; Ito, H.; Noyori, R. J. Am. Chem. Soc. 2000, 122, 1466–1478.
17. Typical procedure for the ruthenacycle-catalyzed b-alkylation of secondary
alcohols with primary alcohols: Primary alcohol (1.0 mmol), secondary alcohol
(1.0 mmol), NaOtBu (1.0 mmol), ruthenium catalyst (1.0 mol %), and toluene
(0.3 mL) were placed in a 10 mL argon-filled, sealed Schlenk tube, and refluxed
at 110 °C for 17 h. The internal standard, 1,3,5-trimethoxybenzene, was added
and the mixture was then filtered through Celite. The solvent was removed on
1. (a) Kose, O.; Saito, S. Org. Biomol. Chem. 2010, 8, 896–900; (b) da Costa, A. P.;
Sanaú, M.; Peris, E.; Royo, B. Dalton Trans. 2009, 6960–6966; (c) Prades, A.;
´
Viciano, M. N.; Sanau, M.; Peris, E. Organometallics 2008, 27, 4254–4259; (d) da
Costa, A. P.; Viciano, M.; Sanaú, M.; Merino, S.; Tejeda, J.; Peris, E.; Royo, B.
Organometallics 2008, 27, 1305–1309; (e) Viciano, M.; Sanaú, M.; Peris, E.
Organometallics 2007, 26, 6050–6054; (f) Martínez, R.; Ramón, D. J.; Yus, M.
Tetrahedron 2006, 62, 8982–8987; (g) Fujita, K.; Asai, C.; Yamaguchi, T.;
Hanasaka, F.; Yamaguchi, R. Org. Lett. 2005, 7, 4017–4019; (h) Xu, C.; Goh, L. Y.;
Pullarkat, S. A. Organometallics 2011, 30, 6499–6502.
a
rotary evaporator to give the respective alcohol. The conversion was

X. Chang et al. / Tetrahedron Letters 53 (2012) 1450–1455
1455
determined by 1H NMR spectroscopy. The signals due to reagents and products
were confirmed by comparison with the literature data.
18. Procedure for the ruthenacycle-catalyzed b-alkylation of secondary alcohols with
primary alcohols: 1,3-diphenyl-2-propenone (1.0 mmol), NaOtBu (1.0 mmol),
ruthenium catalyst 4 (1.0 mol %), and iPrOH (2.0 mL) were placed in a 10 mL
argon-filled sealed Schlenk tube and refluxed at 82 °C for 17 h. The internal
standard, 1,3,5-trimethoxybenzene, was added and the mixture was then
filtered through Celite. The solvent was removed on a rotary evaporator to give
the respective alcohol. The conversion was determined by 1H NMR
spectroscopy. The signals due to reagents and products were compared with
values obtained from the literature.