Ruthenium(II) Complexes with η6-Coordinated 3-Phenylpropanol and 2-Phenylethanol as Catalysts for the Tandem Isomerization/Claisen Rearrangement of Diallyl Ethers in Water

Article abstract of DOI:10.1021/acs.organomet.8b00187

A series of half-sandwich ruthenium(II) complexes containing η⁶-coordinated 2-phenylethanol and 3-phenylpropanol ligands, namely [RuCl₂{η⁶-C₆H₅CH₂(CH₂)_nCH₂OH}(PR₃)] (PR₃ = PMe₃, PPh₃, P(OMe)₃, P(OEt)₃, P(OⁱPr)₃, P(OPh)₃; n = 0 (1a-f), 1 (2a-f)), have been investigated as catalysts for the tandem isomerization/Claisen rearrangement of diallyl ethers into γ,δ-unsaturated aldehydes using, for the first time, water as solvent. The best results in terms of activity and regioselectivity were obtained with the 3-phenylpropanol derivative [RuCl₂(η⁶-C₆H₅CH₂CH₂CH₂OH){P(OEt)₃}] (2d). Thus, using only 1 mol % of this complex, in combination with NaOH (2 mol %), different diallyl ethers could be conveniently converted into the corresponding aldehydes in high yields and short times under relatively mild thermal conditions (100 °C).

Full text of DOI:10.1021/acs.organomet.8b00187

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
Ruthenium(II) Complexes with η6‑Coordinated 3‑Phenylpropanol
and 2‑Phenylethanol as Catalysts for the Tandem Isomerization/
Claisen Rearrangement of Diallyl Ethers in Water
Beatriz Lastra-Barreira, Javier Francos, Pascale Crochet,* and Victorio Cadierno*
́
́
́
Laboratorio de Compuestos Organometalicos y Catalisis (Unidad Asociada al CSIC), Centro de Innovacion en Química Avanzada
́
́
́
(ORFEO-CINQA), Departamento de Química Organica e Inorganica, Instituto Universitario de Química Organometalica “Enrique
́
Moles”, Facultad de Química, Universidad de Oviedo, Julian Clavería 8, E-33006 Oviedo, Spain
S
* Supporting Information
ABSTRACT: A series of half-sandwich ruthenium(II) complexes
containing η6-coordinated 2-phenylethanol and 3-phenylpropanol
ligands, namely [RuCl2{η6-C6H5CH2(CH2)nCH2OH}(PR3)] (PR3
= PMe3, PPh3, P(OMe)3, P(OEt)3, P(OiPr)3, P(OPh)3; n = 0 (1a−
f), 1 (2a−f)), have been investigated as catalysts for the tandem
isomerization/Claisen rearrangement of diallyl ethers into γ,δ-
unsaturated aldehydes using, for the first time, water as solvent. The
best results in terms of activity and regioselectivity were obtained
with the 3-phenylpropanol derivative [RuCl2 (η6 -
C6H5CH2CH2CH2OH){P(OEt)3}] (2d). Thus, using only 1 mol
% of this complex, in combination with NaOH (2 mol %), different
diallyl ethers could be conveniently converted into the corresponding aldehydes in high yields and short times under relatively
mild thermal conditions (100 °C).
ethers, such as the acid- or base-promoted cleavage of allyl
ketals4 or the Hg-catalyzed transfer of a vinyl group from vinyl
ethers to allylic alcohols,5 usually proceed in low yields.6 An
emerging strategy for simplifying the introduction of the vinyl
ether unit is the in situ generation of the allyl vinyl ether
substrates from diallyl ethers, compounds that are much easier
to synthesize, via a metal-catalyzed isomerization of one of the
allyl units (Scheme 2). To avoid the formation of regioisomeric
mixtures of products (or the formation of the corresponding
divinyl ethers), in these tandem isomerization/Claisen
rearrangement (ICR) reactions, diallyl ethers featuring a
substituted carbon atom adjacent to one of the CC bonds
INTRODUCTION
■
Since its discovery in 1912,1 the Claisen rearrangement has
become one of the most widely used synthetic tools for the
selective formation of new C−C bonds.2 In particular, its
aliphatic version starting from allyl vinyl ethers is one of the
most effective methods currently available for the preparation
of γ,δ-unsaturated carbonyl compounds in an atom-economical
manner (Scheme 1). Although these transformations have
Scheme 1. Claisen Rearrangement of the Model Allyl Vinyl
Ether
Scheme 2. Tandem Isomerization/Claisen Rearrangement
(ICR) of Diallyl Ethers
been traditionally performed under strong thermal activation
(ca. 200 °C), a wide number of transition-metal complexes/
salts, Lewis acids, and organocatalysts are now known to
promote the process, allowing the use of milder reaction
conditions compatible with a greater variety of substrates, as
well as the development of asymmetric versions leading to
enantioenriched products.2 Worth noting is also the rate-
acceleration effect exerted by water in these [3,3]-sigmatropic
reactions, a fact that has been associated with the hydrophobic
destabilization of the reactants relative to the polar transition
state, and the stabilization of the latter by hydrogen bonding.3
In addition to stereoselectivity issues,2 the most problematic
aspect associated with this reaction is the access to the starting
materials, since the classical methods for preparing allyl vinyl
Special Issue: In Honor of the Career of Ernesto Carmona
Received: March 30, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00187
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are employed as substrates to ensure the selective isomer-
ization of only one of the two allylic units. To date, catalytic
systems based on ruthenium,7 iridium,8 and to a lesser extent
palladium9 and rhodium10 complexes, have been described for
these ICR processes.11−13 However, it is somewhat surprising
that, despite the growing interest in developing metal catalysis
in environmentally friendly aqueous media14 and the benefits
exerted by water in Claisen rearrangements,3 the feasibility of
ICR reactions in water has not been yet demonstrated, with all
of the examples described in the literature making use of
anhydrous organic solvents as the reaction medium.
Our group has been interested for a long time in aqueous
catalysis, describing different ruthenium(II) and ruthenium-
(IV) complexes able to promote the migration of allylic CC
bonds in aqueous environments. Substrates covered in our
previous works include allyl alcohols,15 ethers,16 amines17 and
benzenes.18 As a continuation, we report herein the successful
application of a series of hydrophilic half-sandwich ruthenium-
(II) complexes, containing η6-coordinated 2-phenylethanol
and 3-phenylpropanol ligands (compounds 1a−f and 2a−f in
Figure 1), in the tandem isomerization/Claisen rearrangement
of diallyl ethers in water.19,20
secondary (3l) carbon atom adjacent to one of the CC
bonds, and different substitution patterns on the olefinic units.
Details on the preparation and characterization of all these
compounds are given in the Supporting Information.21
Concerning the preparation of the arene-ruthenium(II)
complexes [RuCl2(η6-C6H5CH2CH2OH)(PR3)] (1a−f) and
[RuCl2(η6-C6H5CH2CH2CH2OH)(PR3)] (2a−f), they were
obtained in 70−82% yield by reacting the dimeric [{RuCl(μ-
Cl)(η6-C6H5CH2CH2OH)}2] or monomeric [RuCl2{η6:κ1(O)-
C6H5CH2CH2CH2OH}] precursor, respectively, with the
appropriate P-donor ligand in dichloromethane at room
temperature (Scheme 4). As a consequence of the lower
Scheme 4. Synthesis of the Arene-Ruthenium(II)
Complexes 1a−f and 2a−f
solubility of [{RuCl(μ-Cl)(η6-C6H5CH2CH2OH)}2] with
respect to [RuCl2{η6:κ1(O)-C6H5CH2CH2CH2OH}], longer
reaction times were required in the syntheses of the 2-
phenylethanol derivatives 1a−f (12 h vs 2−3 h in the case of
2a−f). As expected, the formation of all these complexes could
be conveniently monitored by 31P{1H} NMR spectroscopy,
the spectra showing a shift of the phosphorus signal to low
fields in the case of the phosphine derivatives 1a,b and 2a,b
(Δδ 25−68 ppm), and to high fields in the case of the
phosphite ones 1c−f amd 2c−f (Δδ −16 to −26 ppm), in
comparison to the corresponding uncoordinated PR3 ligand.
The preparation and characterization of compounds
[RuCl2(η6-C6H5CH2CH2OH)(PPh3)] (1b)19b and
[RuCl2(η6-C6H5CH2CH2CH2OH)(PR3)] (PR3 = PPh3
(2b),19a P(OEt)3 (2d),19c P(OPh)3 (2f)19c) were previously
described by us and others. The rest of the complexes
synthesized in the present work were fully characterized by
means of elemental analysis and IR and multinuclear NMR
spectroscopy, the data obtained being in complete agreement
with the proposed formulations (details are given in the
Figure 1. Structure of the Ru(II) catalysts employed in this work.
RESULTS AND DISCUSSION
■
As the starting point of our investigation, we synthesized the
required diallyl ethers starting from the corresponding allylic
alcohols and bromides, through the general O-alkylation route
outlined in Scheme 3. The substrates covered include diallyl
ethers containing a quaternary (3a−i), tertiary (3j,k), and
Scheme 3. Procedure Employed for the Synthesis of the
Diallyl Ethers 3a−l
1
Experimental Section). In particular, in their H and 13C{1H}
NMR spectra the aromatic CHortho and CHmeta protons and
carbon atoms of the η6-coordinated 2-phenylethanol and 3-
phenylpropanol units were shown to be equivalent, thus
confirming the presence of a symmetry plane in the complexes.
1
The IR and H NMR spectra also confirmed that the OH
groups of these functionalized arenes are maintained
untouched in the final products, showing the characteristic
ν(OH) stretching vibration at 3389−3478 cm−1 and the
proton signal of this functionality at δH 1.82−2.87 ppm (as a
B
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Article
3
triplet for compounds 1a,c−f with JHH = 5.4−6.9 Hz or as a
broad singlet for 2a,c,e), respectively.
remark at this point that, when the same reaction was carried
out in toluene or THF, the desired 2,5-dimethylhept-4-enal
(4a) was generated in much lower yield (≤43% by GC), thus
evidencing for the first time the beneficial effect of water on
ICR reactions (entries 4 and 5). Although the use of biphasic
toluene/H2O and THF/H2O mixtures (1/1 v/v) improved the
results obtained in the pure organic solvents, the effectiveness
of the process was far from that observed in water (entries 6
and 7).
In order to evaluate the feasibility of the tandem
isomerization/Claisen rearrangement (ICR) reactions of
compounds 3 in water and establish the optimal reaction
conditions, we focused on the transformation of 3-(allyloxy)-3-
methylpent-1-ene (3a) into 2,5-dimethylhept-4-enal (4a)
employing complex [RuCl2(η6-C6H5CH2CH2CH2OH){P-
(OiPr)3}] (2e) as a model catalyst. The results of this initial
screening are shown in Table 1.
The ability of complex [RuCl2(η6-C6H5CH2CH2CH2OH)-
{P(OiPr)3}] (2e) to promote the ICR reaction of 3a in the
absence of additives is certainly remarkable, since most
ruthenium-based catalysts previously described in the literature
require the addition of an acid or a base to be active.7 On this
basis, and with the aim of improving the effectiveness shown
by 2e, we decided to explore its behavior in the presence of
different additives. Thus, as shown in entry 8, we found that
the catalytic activity of 2e is not affected by the addition of the
chloride abstractor AgSbF6 (1 mol %). This result indicates
that cleavage of the Ru−Cl bonds, required to generate vacant
sites on the metal for substrate binding, is not the rate-limiting
step of the process. On the other hand, although in the
presence of acid, i.e. 1 mol % of HCl, quantitative conversion
of the diallyl ether 3a was observed after 6 h, the yield in the
aldehyde 4a was in this case much lower (62%; Table 1, entry
9). This is because the acid favors the hydrolysis of the allyl
vinyl ether intermediate, thus leading, as assessed by GC, to
the formation of propanal and 3-methylpent-1-en-3-ol as
byproducts. Finally, we observed that the addition of a base (1
or 2 mol % of NaOH) accelerates the process, leading also to
the quantitative conversion of the diallyl ether 3a (entries 10
and 11). In terms of 4a yield the best result was obtained with
2 mol % of NaOH, an experiment that led to the formation of
the aldehyde in 98% GC yield (E:Z ratio 58:42), with only 2%
of allyl vinyl ether intermediate being detected in the
chromatogram. Concerning the stereoselectivity of the
reaction, no major changes were observed in any of these
experiments.
From this initial screening with complex 2e, we decided to
use NaOH (2 mol %) in the rest of the catalytic experiments.
At this point we wish to emphasize that the use of a low metal
loading (1 mol %), in combination with a low temperature
(100 °C), is a novelty in ICR reactions promoted by
ruthenium. In fact, in most of the examples described to
date, catalysts loadings of 5−8 mol % of Ru were employed
(with temperatures in the range 80−120 °C),7c−j and those
that operate with lower metal loadings do so at temperatures
above 150 °C.7a,b
With the optimized experimental conditions in hand, i.e. 1
mol % of Ru, 2 mol % of NaOH, pure water, and 100 °C, the
catalytic activity of the rest of the ruthenium(II) complexes
synthesized was subsequently evaluated, employing again the
diallyl ether 3a as a model substrate. As shown in Table 2, the
nature of the η6-arene ligand, i.e. 2-phenylethanol (1a−f) or 3-
phenylpropanol (2a−f), practically does not exert any effect on
the catalytic activity of the complexes or on the stereo-
selectivity of the process (even vs odd entries). In contrast, the
outcome of the reaction was strongly dependent on the
auxiliary P-donor ligand coordinated to ruthenium. Thus, while
all those complexes containing aliphatic phosphite ligands, i.e.
compounds 1c−e and 2c−e, gave rise to the quantitative
conversion of the starting material after 6 h (entries 5−10),
incomplete conversions were observed with the corresponding
Table 1. Catalytic ICR of 3-(Allyloxy)-3-methylpent-1-ene
(3a) Using the Ru(II) Complex [RuCl2(η6-
a
C6H5CH2CH2CH2OH){P(OiPr)3}] (2e) as Catalyst
conversion
yield of
E:Z
c
b
b
entry
solvent
H2O
H2O
H2O
toluene
THF
toluene/
H2O
THF/
H2O
H2O
H2O
H2O
H2O
additive T (°C)
(%)
4a (%)
ratio
1
2
3
4
5
none
none
none
none
none
none
60
80
100
100
100
100
18
65
91
28
31
46
17
62
91
24
27
43
57:43
57:43
57:43
57:43
58:42
58:42
d
6
d
7
none
100
60
40
58:42
e
8
AgSbF6
HCl
NaOH
NaOH
100
100
100
100
90
>99
>99
>99
90
62
93
98
57:43
57:43
57:43
58:42
e
9
ef
,
10
11
g
a
Reactions performed under an argon atmosphere using 2 mmol of
3a, 0.02 mmol of 2e, and 1 mL of the corresponding solvent.
Conversions and yields determined by GC. The differences between
conversions and yields correspond to the intermediate allyl vinyl ether
present in the reaction media. E:Z ratios determined by H NMR
spectroscopy after evaporation of the solvent. A 1/1 v/v mixture of
solvents was employed. Reaction performed with 1 mol % of the
additive. Propanal and 3-methylpent-1-en-3-ol were in this case the
b
c
1
d
e
f
g
major byproducts detected by GC. Reaction performed with 2 mol %
of the additive.
Thus, a first experiment carried out directly in water with 1
mol % of 2e, at 60 °C and in the absence of additives, led to a
poor conversion of the diallyl ether 3a (18% by GC) after 6 h
(Table 1, entry 1). However, we were delighted to find that
this initial result could be significantly improved by increasing
the working temperature (entries 2 and 3). In particular, when
the reaction was performed at 100 °C, 91% conversion of 3a
was observed by GC after the same time and, more
importantly, under these conditions only 2,5-dimethylhept-4-
enal (4a) was formed (entry 3). At lower temperatures, in
addition to the desired aldehyde, minor amounts of a
secondary product were present in the chromatograms (entries
1 and 2), which correspond to the nonrearranged allyl vinyl
ether intermediate resulting from the initial migration of the
CC bond of the −OCH2CHCH2 unit of 3a (see Scheme
2). Also of note is the null effect that the temperature exerts on
the stereoselectivity of the reaction, the aldehyde 4a being in
all cases formed as a mixture of E and Z isomers in a 57:43
ratio (entries 1−3).22 On the other hand, we would like also to
C
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Table 2. ICR of the Diallyl Ether 3a Catalyzed by Complexes [RuCl2{η6-C6H5CH2(CH2)nCH2OH}(PR3)] (1a−f and 2a−f) in
a
Water
b
b
c
entry
catalyst
time (h)
conversion (%)
yield (%)
E:Z ratio
1
2
3
4
5
6
7
8
1a (n = 0; PR3 = PMe3)
2a (n = 1; PR3 = PMe3)
1b (n = 0; PR3 = PPh3)
6
6
6
6
6
6
73
75
47
45
>99
69
70
45
41
96
94
57:43
58:42
57:43
58:42
55:45
55:45
58:42
59:41
58:42
58:42
58:42
58:42
2b (n = 1; PR3 = PPh3)
1c (n = 0; PR3 = P(OMe)3)
2c (n = 1; PR3 = P(OMe)3)
1d (n = 0; PR3 = P(OEt)3)
2d (n = 1; PR3 = P(OEt)3)
1e (n = 0; PR3 = P(OiPr)3)
2e (n = 1; PR3 = P(OiPr)3)
1f (n = 0; PR3 = P(OPh)3)
2f (n = 1; PR3 = P(OPh)3)
>99
6 (4)
6 (4)
>99 (>99)
>99 (>99)
>99
>99 (97)
>99 (>99)
9
6
6
6
6
98
97
29
25
10
11
12
>99
37
35
a
Reactions performed under an argon atmosphere using 2 mmol of 3a, 0.02 mmol of the corresponding Ru(II) complex 1a−f and 2a−f, 0.04 mmol
b
of NaOH, and 1 mL of water. Conversions and yields determined by GC. The differences between conversions and yields correspond to the
intermediate allyl vinyl ether present in the reaction media. E:Z ratios determined by H NMR spectroscopy after evaporation of the solvent.
c
1
phosphine derivatives 1a,b and 2a,b (entries 1−4) and
compounds 1f and 2f containing an aromatic phosphite
(entries 11 and 12). These observations are consistent with
our previous results in the isomerization of allylic alcohols and
allylbenzenes in water with the related arene-ruthenium(II)
complexes [RuCl2(η6-C6H5OCH2CH2OH)(PR3)],15g,18a,c for
which the highest catalytic activities were observed with
aliphatic phosphites due to the high solubility in water that
these types of ligands give to their complexes.23 According to
the water solubility measurements carried out with complexes
1a−f and 2a−f, the same explanation can also be given in the
present case (30−120 mg/mL for 1c−e and 2c−e vs <0.5 mg/
mL for 1a,b,f and 2a,b,f at room temperature). Among the
aliphatic phosphite complexes 1c−e and 2c−e, the best results
were obtained with [RuCl2{η6-C6H5CH2(CH2)nCH2OH}{P-
(OEt)3}] (n = 0 (1d), 1 (2d)), which were able to generate
the γ,δ-unsaturated aldehyde 4a in quantitative GC yield
(entries 7 and 8). Additional experiments at a shorter time (4 h
instead of 6 h) allowed us to identify the 3-phenylpropanol
derivative 2d as the most effective catalyst of the series. Finally,
with regard to the stereoselectivity of the reaction, it was little
affected by the nature of the catalyst employed (E:Z ratios
from 55:45 to 59:41).
On the other hand, it is known that 3-phenylpropanol
derivatives [RuCl2(η6-C6H5CH2CH2CH2OH)(PR3)] readily
generate cationic tethered species [RuCl{η6:κ1(O)-
C6H5CH2CH2CH2OH}(PR3)]+ by abstraction of one of the
chloride ligands.19a,c,24 This fact prompted us to investigate the
catalytic behavior of the known complex [RuCl{η6:κ1(O)-
C6H5CH2CH2CH2OH}{P(OEt)3}][SbF6] (5) in order to
determine if a change in the coordination mode of the arene
ligand has any effect on the catalytic reaction. As shown in
Scheme 5, complex 5 is accessible by treatment of a
dichloromethane solution of 2d with silver hexafluoroantimo-
nate.19c Although a higher catalytic activity of 5 vs 2d could be
anticipated on the basis of on easier dissociation of the alcohol
group, the experimental result was just the opposite. Thus,
under reaction conditions identical with those employed in
Table 2, incomplete transformation of the diallyl ether 3a was
Scheme 5. Synthesis of the Tethered Ruthenium(II)
Complex 5
observed after 6 h (93% conversion with a selectivity toward
aldehyde 4a of 87%, in comparison with entry 8). Solubility
issues could be behind of this inferior performance again since,
despite its ionic nature, 5 is very poorly soluble in water (2.3
mg/mL vs 101.5 mg/mL in the case of 2d).25
In addition, to get insight into the mechanism, we studied
the behavior of complexes [RuCl2(η6-C6H5CH2CH2CH2OH)-
(PR3)] (2a−f) in pure water as well as in aqueous NaOH
solutions, the conditions employed for the catalytic experi-
ments. As a general trend, three species, which coexist in
equilibrium,26 were observed by NMR spectroscopy in pure
w a t er : t he di c h l o r i d e p r ec u r s o r [ R u C l2 (η6 -
C6H5CH2CH2CH2OH)(PR3)], detected as the major com-
pound in all of the cases, the aquo derivative [RuCl(H2O)(η6-
C6H5CH2CH2CH2OH)(PR3)][Cl], and the tethered complex
[RuCl(η6:κ1(O)-C6H5CH2CH2CH2OH)(PR3)][Cl]. Upon ad-
dition of NaOH to these aqueous solutions, different chemical
processes take place, the outcome of the reactions depending
on the nature of the phosphorated ligand. As an example, the
phosphine complex [RuCl2(η6-C6H5CH2CH2CH2OH)-
(PMe3)] (2a) gave rise to the formation of two new
organometallic products, tentatively assigned to the hydroxo
species [Ru(H2O)(OH)(η6-C6H5CH2CH2CH2OH)(PMe3)]-
[Cl] and [Ru(OH)(η6:κ1(O)-C6H5CH2CH2CH2OH)-
(PMe3)][Cl].27,28 However, when the P(OMe)3-containing
derivative [RuCl2(η6-C6H5CH2CH2CH2OH){P(OMe)3}]
(2c) was involved in the reaction, formation of the dimethyl
phosphite compounds [RuCl2(η6-C6H5CH2CH2CH2OH){P-
( O M e ) 2 ( O H ) } ] a n d [ R u C l ( η 6 : κ 1 ( O ) -
D
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C6H5CH2CH2CH2OH){P(OMe)2(OH)}][Cl] was ob-
served,29 along with methanol, as the result of the attack of
OH− anions to the coordinated phosphite ligand. Therefore,
the superior activity of the phosphite catalysts, respective to
the phosphine species, is probably related not only to solubility
issues but also to their ability to generate species with a
coordinated P(OR)2(OH) ligand. In summary, the main role
of NaOH during the catalytic reactions is to promote the
formation of a P(OR)2(OH) ligand, which could cooperate
with the metal in the initial allyl unit isomerization step (see
Scheme 6).30
group that is not isomerized in the first step. Thus, starting
from diallyl ether 3g, the novel γ,δ-unsaturated aldehyde 4g
could be synthesized in 94% yield after only 1.5 h of reaction
(entry 7). As a consequence of the Claisen rearrangement, two
stereogenic centers are generated in this case, and 4g was
isolated as a nonseparable mixture of the corresponding syn
and anti diastereoisomers in a ca. 1:1 ratio.
To our delight, despite the diallyl ethers 3j,k bear two
potentially isomerizable allyl units due to the presence of only
one substituent in a position α to oxygen, a high regiocontrol
was observed in their reactions, which afforded selectively the
aldehydes 4j,k, respectively, resulting from the exclusive
isomerization of the CH2CHCH2 unit (Table 3, entries 10
and 11). In addition, the stereoselectivity of the ICR process
was very high in these cases, delivering the products as the E
isomers. Nonetheless, as observed for 4g, in the case of 4k a
mixture of syn and anti diastereoisomers in a ca. 1:1 ratio was
formed. Finally, concerning the diallyl ether 3l (entry 12), in
which no substituents adjacent to the CC bonds are present,
the reaction led after a short time to a complex mixture of
Scheme 6. Tentative Role of the in Situ Formed
P(OR)2(OH) Ligands
1
products that, due to the signals overlapping in the H NMR
spectrum, could not be identified (we do not rule out that in
addition to the expected aldehydes 4l and 4l′ the intermediate
allyl vinyl ethers were also present in the mixture).
The scope of the process was subsequently evaluated
employing the whole family of diallyl ethers 3a−l (Scheme
3) and the most active catalyst 2d. In all of the cases, the
reactions were carried out in water at 100 °C, with a ruthenium
loading of 1 mol %, and in the presence of 2 mol % of NaOH.
The results obtained are shown in Table 3. As observed for 3a
(entry 1), the diallyl ethers 3b−f, also containing a quaternary
carbon atom in a position α to oxygen and featuring
nonsubstituted olefinic CHCH2 units, could be completely
and chemoselectively transformed into the corresponding γ,δ-
unsaturated aldehydes 4b−f, which were isolated after
chromatographic workup in 85−94% yield (entries 2−6). At
the end of the reactions, which required short times in general
(1.5−9 h), the intermediate allyl vinyl ethers or other
byproducts were not detected by GC in the crude products,
even in the case of compound 3f, where an extra CC bond is
present (entry 6). For diallyl ethers 3c,e,f, which contain two
different substituents on the α-carbon atom, the corresponding
aldehydes were generated as mixtures of E and Z isomers
(entries 3, 5, and 6). When these substituents are aliphatic
groups, the E:Z ratios in the aldehydes (4c,f) are very similar
to those observed for 4a, i.e. ca. 60:40 (entries 3 and 6). In
contrast, the stereoselectivity achieved in the case of aldehyde
4e was much higher (E:Z ratio 72:28; entry 5) as a
consequence of the stronger electronic and steric differences
between the methyl and phenyl substituents.31
More disparate results were obtained when substrates
containing nonterminal olefinic units were employed. Thus,
when substituents were present in the allyl group that has to be
isomerized, the catalytic activity of complex 2d decreased
drastically, with conversions of up to 17% after 24 h of heating
(Table 3, entries 8 and 9). This behavior, observed regardless
of whether the substituent is located on the internal (diallyl
ether 3h; entry 8) or external olefinic carbon (diallyl ether 3i;
entry 9), stems from the sterically disfavored coordination of
the CC bond to ruthenium, which results in a drastic rate
decrease in the initial isomerization step (Scheme 2).32
Conversely, the effectiveness of the ICR process was not
affected by the introduction of a substituent on the olefin
CONCLUSION
■
In summary, we have demonstrated that hydrophilic arene-
ruthenium(II) complexes of general composition [RuCl2{η6-
C6H5CH2(CH2)nCH2OH}(PR3)] (n = 0, 1; PR3 = phosphine,
phosphite) are able to catalyze, in combination with NaOH,
tandem isomerization/Claisen rearrangement (ICR) reactions
of diallyl ethers in water. In particular, the 3-phenylpropanol
derivative [RuCl2(η6-C6H5CH2CH2CH2OH){P(OEt)3}] (2d)
proved to be the most efficient, allowing the high-yield
formation of different γ,δ-unsaturated aldehydes starting from
diallyl ethers featuring a quaternary or tertiary carbon atom
adjacent to one of the CC bonds. Remarkably, in
comparison to other ruthenium catalysts previously described
in the literature, complex 2d stands out for its high activity at a
low metal loading (1 mol %) and under relatively mild
temperature conditions (100 °C). Its efficiency seems to be
related to its ability to generate P(OEt)2(OH)-containing
species under the basic conditions employed. In addition, it is
the first metal catalyst able to promote ICR processes in water,
an environmentally friendly reaction medium whose use has
also been demonstrated to be beneficial in these types of
tandem transformations of olefins.
EXPERIMENTAL SECTION
■
Synthetic procedures were performed under an atmosphere of dry
argon using vacuum-line and standard Schlenk or sealed-tube
techniques. Solvents were dried by standard methods and distilled
under argon before use.33 The ruthenium complexes [{RuCl(μ-
C l ) ( η 6 - C 6 H 5 C H 2 C H 2 O H ) } 2 ] , 3 4 [ R u C l 2 { η 6 : κ 1 ( O ) -
C6H5CH2CH2CH2OH}],19a,35 [RuCl2(η6-C6H5CH2CH2OH)(PPh3)]
(1b),19b [RuCl2(η6-C6H5CH2CH2CH2OH)(PR3)] (PR3 = PPh3
(2b),19a P(OEt)3 (2d),19c P(OPh)3 (2f)19c), and [RuCl{η6:κ1(O)-
C6H5CH2CH2CH2OH}{P(OEt)3}][SbF6] (5),19c were prepared by
following the methods reported in the literature. The diallyl ethers
3a−l were synthesized by allylation of the corresponding allylic
alcohol as detailed in the Supporting Information. Infrared spectra
were recorded on a PerkinElmer 1720-XFT spectrometer. NMR
spectra were recorded at 25 °C on Bruker DPX-300 and AV400
instruments. The chemical shift values (δ) are given in parts per
E
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Article
a
Table 3. ICR of the Diallyl Ethers 3a−l Catalyzed by Complex [RuCl2(η6-C6H5CH2CH2CH2OH){P(OEt)3}] (2d) in Water
a
Reactions performed under an argon atmosphere using 2 mmol of the corresponding diallyl ether 3, 0.02 mmol of the Ru(II) complex 2d, 0.04
b
c
mmol of NaOH, and 1 mL of water. Conversions determined by GC. Yields determined by GC. Isolated yields after chromatographic workup are
given in parentheses. E:Z ratios determined by H NMR spectroscopy. The corresponding aldehyde is generated as a mixture of syn and anti
d
e
1
diastereoisomers in a ca. 1:1 ratio.
́
million and are referenced to the residual peak of the deuterated
solvent employed (1H and 13C). DEPT experiments have been carried
out for all of the compounds reported in this paper. GC
measurements were made on a Hewlett-Packard HP6890 apparatus
(Supelco Beta-Dex 120 column, 30 m length, 250 μm diameter).
Elemental analyses were provided by the Analytical Service of the
Instituto de Investigaciones Quimicas (IIQ-CSIC) of Seville. HRMS
data were obtained on a QTOF Bruker Impact II mass spectrometer
in the General Services of the University of Oviedo. For column
chromatography, Merck silica gel 60 (230−400 mesh) was employed.
General Procedure for the Preparation of Complexes
[RuCl2(η6-C6H5CH2CH2OH)(PR3)] (PR3 = PMe3 (1a), P(OMe)3
F
DOI: 10.1021/acs.organomet.8b00187
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Organometallics
Article
(1c), P(OEt)3 (1d), P(OiPr)3 (1e), P(OPh)3 (1f)). A suspension of the
dimer [{RuCl(μ-Cl)(η6-C6H5CH2CH2OH)}2] (0.300 g, 0.510
mmol) and the corresponding phosphite or phosphine ligand (1.22
mmol) in CH2Cl2 (50 mL) was stirred, at room temperature,
overnight. The reaction mixture was then filtered through Kieselguhr
to eliminate small quantities of the undissolved starting material, and
the filtrate was evaporated to dryness. The residue was washed with
diethyl ether (3 × 5 mL) and the resulting reddish orange solid dried
in vacuo. Data for 1a are as follows. Yield: 0.306 g (81%). IR (KBr): ν
C6H5CH2CH2CH2OH}] (0.308 g, 1 mmol) and the corresponding
phosphite or phosphine ligand (1.2 mmol) in CH2Cl2 (50 mL) was
stirred, at room temperature, until complete dissolution of the starting
Ru complex (ca. 2−3 h). The reaction mixture was then evaporated to
dryness, and the residue was washed with diethyl ether (3 × 5 mL) to
give a reddish orange solid which was dried in vacuo. Data for 2a are
as follows. Yield: 0.288 g (75%). IR (KBr): ν 3391 (br, O−H) cm−1.
31P{1H} NMR (CD2Cl2): δ 6.3 (s) ppm. 1H NMR (CD2Cl2): δ 5.52
(td, 3JHH = 4.8 Hz, 3JPH = 2.1 Hz, 2H, CHmeta), 5.43 (d, 3JHH = 4.8 Hz,
1
3389 (br, O−H) cm−1. 31P{1H} NMR (CD2Cl2): δ 6.6 (s) ppm. H
3
2H, CHortho), 5.11 (t, JHH = 4.8 Hz, 1H, CHpara), 3.76 (m, 2H,
3
3
NMR (CD2Cl2): δ 5.61 (d, JHH = 6.0 Hz, 2H, CHortho), 5.41 (ddd,
CH2OH), 2.64 (t, JHH = 7.5 Hz, 2H, CH2Ph), 2.15 (br s, 1H, OH),
3JHH = 6.0 and 5.4 Hz, 3JPH = 1.5 Hz, 2H, CHmeta), 5.24 (td, 3JHH = 5.4
Hz, 3JPH = 2.4 Hz, 1H, CHpara), 4.03 (m, 2H, CH2OH), 2.87 (t, 3JHH
= 6.9 Hz, 1H, OH), 2.78 (t, 3JHH = 5.1 Hz, 2H, CH2Ph), 1.64 (d, 2JPH
= 11.4 Hz, 9H, Me) ppm. 13C{1H} NMR (CD2Cl2): δ 106.6 (s,
Cipso), 89.2 and 84.9 (s, CHortho and CHmeta), 79.9 (s, CHpara), 60.4 (s,
2
1.98−1.89 (m, 2H, CH2CH2Ph), 1.63 (d, JPH = 11.1 Hz, 9H, Me)
ppm. 13C{1H} NMR (CDCl3): δ 110.7 (d, 2JPC = 6.0 Hz, Cipso), 86.9
2
(d, JPC = 5.7 Hz, CHortho or CHmeta), 86.6 (s, CHortho or CHmeta),
78.3 (s, CHpara), 61.3 (s, CH2OH), 31.2 and 28.9 (s, CH2CH2Ph),
1
16.7 (d, JPC = 34.8 Hz, Me) ppm. Anal. Calcd for C12H21Cl2OPRu:
1
CH2OH), 35.7 (s, CH2Ph), 16.2 (d, JPC = 33.9 Hz, Me) ppm. Anal.
C, 37.51; H, 5.51. Found: C, 37.62; H, 5.48. Data for 2c are as
follows. Yield: 0.337 g (78%). IR (KBr): ν 3478 (br, O−H) cm−1.
Calcd for C11H19Cl2OPRu: C, 35.69; H, 5.17. Found: C, 35.60; H,
5.25. Data for 1c are as follows. Yield: 0.311 g (73%). IR (KBr): ν
3421 (br, O−H) cm−1. 31P{1H} NMR (CD2Cl2): δ 119.0 (s) ppm.
1
31P{1H} NMR (CD2Cl2): δ 119.7 (s) ppm. H NMR (CD2Cl2): δ
3
3
5.64 (t, JHH = 5.4 Hz, 2H, CHmeta), 5.53 (d, JHH = 5.4 Hz, 2H,
3
1H NMR (CD2Cl2): δ 5.70 (d, JHH = 5.7 Hz, 2H, CHortho), 5.59
3
CHortho), 5.38 (t, JHH = 5.4 Hz, 1H, CHpara), 3.81−3.77 (m, 2H,
3
3
CH2OH), 3.79 (d, 3JPH = 11.1 Hz, 9H, OMe), 2.71 (t, 3JHH = 7.5 Hz,
2H, CH2Ph), 2.05 (br s, 1H, OH), 1.99−1.90 (m, 2H, CH2CH2Ph)
ppm. 13C{1H} NMR (CDCl3): δ 114.7 (d, 2JPC = 6.3 Hz, Cipso), 90.0
and 88.7 (s, CHortho and CHmeta), 81.0 (s, CHpara), 61.0 (s, CH2OH),
(ddd, JHH = 5.7 and 5.4 Hz, JPH = 1.5 Hz, 2H, CHmeta), 5.48 (td,
3JHH = 5.4 Hz, JPH = 2.4 Hz, 1H, CHpara), 4.05 (m, 2H, CH2OH),
3
3.79 (d, 3JPH = 11.1 Hz, 9H, OMe), 2.82 (td, 3JHH = 6.0 Hz, 3JPH = 2.1
Hz, 2H, CH2Ph), 2.57 (t, JHH = 6.0 Hz, 1H, OH) ppm. 13C{1H}
3
NMR (CDCl3): δ 111.6 (d, 2JPC = 10.2 Hz, Cipso), 92.0 (d, 2JPC = 6.9
2
54.2 (d, JPC = 5.6 Hz, OMe), 31.2 and 28.9 (s, CH2CH2Ph) ppm.
Hz, CHortho or CHmeta), 87.5 (s, CHortho or CHmeta), 81.9 (s, CHpara),
Anal. Calcd for C12H21O4Cl2PRu: C, 33.35; H, 4.90. Found: C, 33.57;
H, 4.95. Data for 2e are as follows. Yield: 0.423 g (82%). IR (KBr): ν
3452 (br, O−H) cm−1. 31P{1H} NMR (CD2Cl2): δ 107.5 (s) ppm.
2
60.6 (s, CH2OH), 54.3 (d, JPC = 5.6 Hz, OMe), 35.7 (s, CH2Ph)
ppm. Anal. Calcd for C11H19O4Cl2PRu: C, 31.59; H, 4.58. Found: C,
31.44; H, 4.67. Data for 1d are as follows. Yield: 0.347 g (74%). IR
(KBr): ν 3445 (br, O−H) cm−1. 31P{1H} NMR (CD2Cl2): δ 113.7
(s) ppm. 1H NMR (CD2Cl2): δ 5.68 (d, 3JHH = 6.0 Hz, 2H, CHortho),
3
1H NMR (CD2Cl2): δ 5.55 (t, JHH = 5.4 Hz, 2H, CHmeta), 5.43 (d,
3
3JHH = 5.4 Hz, 2H, CHortho), 5.29 (t, JHH = 5.4 Hz, 1H, CHpara),
3
4.94−4.83 (m, 3H, OCH(CH3)2), 3.78 (t, JHH = 5.7 Hz, 2H,
5.54 (dd, 3JHH = 6.0 and 5.4 Hz, 2H, CHmeta), 5.45 (td, 3JHH = 5.4 Hz,
3
CH2OH), 2.70 (t, JHH = 6.9 Hz, 2H, CH2Ph), 1.99−1.91 (m, 2H,
3
3JPH = 2.4 Hz, 1H, CHpara), 4.16 (quint, JPH
=
3JHH = 7.2 Hz,
3
CH2CH2Ph), 1.82 (br s, 1H, OH), 1.32 (d, JHH = 6.0 Hz, 18H,
3
3
2
OCH(CH3)2) ppm. 13C{1H} NMR (CDCl3): δ 114.7 (d, JPC = 8.9
OCH2CH3), 4.04 (m, 2H, CH2OH), 2.81 (td, JHH = 5.7 Hz, JPH
=
=
1.5 Hz, 2H, CH2Ph), 2.66 (t, 3JHH = 5.7 Hz, 1H, OH), 1.32 (t, 3JHH
Hz, Cipso), 89.8 (d, 2JPC = 7.9 Hz, CHortho or CHmeta), 88.6 (s, CHortho
7.2 Hz, 9H, OCH2CH3) ppm. 13C{1H} NMR (CDCl3): δ 110.9 (d,
2JPC = 12.5 Hz, Cipso), 92.1 (d, 2JPC = 7.4 Hz, CHortho or CHmeta), 87.0
2
or CHmeta), 81.5 (s, CHpara), 72.0 (d, JPC = 7.2 Hz, OCH(CH3)2),
3
61.5 (s, CH2OH), 30.9 and 28.6 (s, CH2CH2Ph), 24.4 (d, JPC = 3.8
2
(s, CHortho or CHmeta), 82.3 (s, CHpara), 63.2 (d, JPC = 4.0 Hz,
OCH2CH3), 60.6 (s, CH2OH), 35.7 (s, CH2Ph), 16.2 (d, JPC = 7.0
Hz, OCH(CH3)2) ppm. Anal. Calcd for C18H33O4Cl2PRu: C, 41.87;
H, 6.44. Found: C, 41.82; H, 6.51.
3
Hz, OCH2CH3) ppm. Anal. Calcd for C14H25O4Cl2PRu: C, 36.53; H,
5.47. Found: C, 36.62; H, 5.56. Data for 1e are as follows. Yield: 0.359
g (70%). IR (KBr): ν 3403 (br, O−H) cm−1. 31P{1H} NMR
(CD2Cl2): δ 106.9 (s) ppm. 1H NMR (CD2Cl2): δ 5.64 (d, 3JHH = 5.4
Hz, 2H, CHortho), 5.49−5.43 (m, 3H, CHmeta and CHpara), 4.88 (m,
General Procedure for ICR Reactions Catalyzed by Complex
[RuCl2(η6-C6H5CH2CH2CH2OH){P(OEt)3}] (2d). Under an argon
atmosphere, the corresponding diallyl ether 3 (2 mmol), water (1
mL), the ruthenium(II) complex 2d (0.009 g, 0.02 mmol; 1 mol %),
and NaOH (0.0016 g, 0.04 mmol; 2 mol %) were introduced into a
Teflon-capped sealed tube, and the reaction mixture was stirred at 100
°C for the indicated time (see Table 3). The course of the reaction
was monitored by regularly taking samples of ca. 10 μL which, after
extraction with CH2Cl2 (3 mL), were analyzed by GC. Once the
maximum conversion of the starting substrate was reached, the
solvent was removed under vacuum and the crude reaction mixture
purified by column chromatography (silica gel) employing a EtOAc/
hexanes mixture (1/10) as eluent. Characterization data for the
isolated γ,δ-unsaturated aldehydes 4 are as follows.
3
3H, OCH(CH3)2), 4.05 (m, 2H, CH2OH), 2.81 (td, JHH = 5.7 Hz,
3JPH = 1.8 Hz, 2H, CH2Ph), 2.74 (t, 3JHH = 5.7 Hz, 1H, OH), 1.32 (d,
3JHH = 6.0 Hz, 18H, OCH(CH3)2) ppm. 13C{1H} NMR (CDCl3): δ
2
2
110.1 (d, JPC = 12.1 Hz, Cipso), 92.5 (d, JPC = 7.9 Hz, CHortho or
CHmeta), 86.4 (s, CHortho or CHmeta), 82.9 (s, CHpara), 71.7 (d, 2JPC
=
7.6 Hz, OCH(CH3)2), 60.5 (s, CH2OH), 35.4 (s, CH2Ph), 24.0 (d,
3JPC = 2.9 Hz, OCH(CH3)2) ppm. Anal. Calcd for C17H31O4Cl2PRu:
C, 40.64; H, 6.22. Found: C, 40.77; H, 6.35. Data for 1f are as follows.
Yield: 0.475 g (77%). IR (KBr): ν 3412 (br, O−H) cm−1. 31P{1H}
2,5-Dimethylhept-4-enal (4a).36 Isolated as a nonseparable
mixture of E and Z isomers in 59:41 ratio. Colorless oil. Yield:
0.258 g (92%). HRMS (ESI): m/z 141.1275, [M + H+] (calcd for
1
NMR (CD2Cl2): δ 111.0 (s) ppm. H NMR (CD2Cl23): δ 7.46−7.39
(m, 11H, OPh), 7.30−7.25 (m, 4H, OPh), 5.33 (d, JHH = 6.3 Hz,
3
3
2H, CHortho), 5.01 (ddd, JHH = 6.3 and 5.7 Hz, JPH = 1.5 Hz, 2H,
1
CHmeta), 4.51 (td, 3JHH = 5.7 Hz, 3JPH = 2.1 Hz, 1H, CHpara), 3.95 (m,
C9H17O: 141.1279). NMR data for the E isomer are as follows. H
3
3
NMR (CDCl3): δ 9.65 (s, 1H, CHO), 5.13−5.04 (m, 1H, CH),
2.42−2.38 (m, 2H, CH2), 2.06−1.99 (m, 3H, CH and CH2), 1.63 (s,
3H, CCH3), 1.02−0.95 (m, 6H, CH3) ppm. 13C{1H} NMR
(CDCl3): δ 205.1 (s, CHO), 139.5 (s, = C), 119.0 (s, CH), 46.8 (s,
CH), 32.3 and 28.9 (s, CH2), 22.8 (s, CCH3), 12.9 and 12.7 (s,
2H, CH2OH), 2.66 (td, JHH = 5.4 Hz, JPH = 2.1 Hz, 2H, CH2Ph),
2.31 (t, JHH = 5.4 Hz, 1H, OH) ppm. 13C{1H} NMR (CD2Cl2): δ
3
151.1 (d, 2JPC = 9.2 Hz, Cipso of OPh), 129.7 (s, Cmeta of OPh), 125.4
(s, Cpara of OPh), 121.6 (d, 3JPC = 4.3 Hz, (s, Cortho of OPh), 113.0 (d,
2JPC = 9.6 Hz, Cipso), 91.8 (d, 2JPC = 8.1 Hz, CHortho or CHmeta), 87.9
1
CH3) ppm. NMR data for the Z isomer are as follows. H NMR
(s, CHortho or CHmeta), 80.3 (s, CHpara), 60.2 (s, CH2OH), 35.6 (s,
CH2Ph) ppm. Anal. Calcd for C26H25O4Cl2PRu: C, 51.67; H, 4.17.
Found: C, 51.77; H, 4.21.
General Procedure for the Preparation of Complexes
[RuCl2(η6-C6H5CH2CH2CH2OH)(PR3)] (PR3 = PMe3 (2a), P(OMe)3
(2c), P(OiPr)3 (2e)). A suspension of the complex [RuCl2{η6:κ1(O)-
(CDCl3): δ 9.66 (s, 1H, CHO), 5.13−5.04 (m, 1H, CH), 2.42−
2.38 (m, 2H, CH2), 2.06−1.99 (m, 3H, CH and CH2), 1.11 (s, 3H,
CCH3), 1.02−0.95 (m, 6H, CH3) ppm. 13C{1H} NMR (CDCl3): δ
205.1 (s, CHO), 139.5 (s, C), 120.1 (s, CH), 46.8 (s, CH), 28.6
and 24.7 (s, CH2), 15.9 (s, CCH3), 13.0 and 12.5 (s, CH3) ppm.
G
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2,5-Dimethylhex-4-enal (4b).7a Colorless oil. Yield: 0.227 g
1H, CHCH3, syn and anti), 1.64 and 1.61 (d, 3H, JHH = 1.2 Hz, 
CHCH3, syn and anti), 1.54 (br, 3H, CHCH3, syn and anti), 1.01
3
1
3
(90%). H NMR (C6D6): δ 9.46 (s, 1H, CHO), 5.06 (t, 1H, JHH
= 6.2 Hz, CH), 2.25−2.19 (m, 1H, CH), 2.10−1.92 (m, 2H, CH2),
and 0.85 (d, 3H, JHH = 6.9 Hz, CH3, syn and anti) ppm. 13C{1H}
3
3
1.66 and 1.62 (s, 3H each, CCH3), 0.92 (d, 3H, JHH = 7.2 Hz,
NMR (C6D6): δ 203.2 and 202.9 (s, CHO, syn and anti), 143.0 and
142.7 (s, Cipso, syn and anti), 133.3 and 133.0 (s, = C, syn and anti),
128.6 (s, CHmeta, syn and anti), 127.9 and 127.8 (s, CHortho, syn and
anti), 126.3 (s, CHpara, syn and anti), 126.0 and 124.8 (s, CH, syn
and anti), 51.7 and 51.6 (s, CHCH3, syn and anti), 46.2 and 45.3 (s,
CHPh, syn and anti), 25.6, 25.5, and 17.9 (2C) (s, CHCH3, syn
and anti), 12.3 and 11.2 (s, CH3, syn and anti) ppm.
CH3) ppm. 13C{1H} NMR (C6D6): δ 203.3 (s, CHO), 146.6 (s, 
C), 121.1 (s, CH), 46.5 (s, CH), 29.0 (s, CH2), 25.6 and 25.5 (s,
CCH3), 12.7 (s, CH3) ppm.
2,5-Dimethylundec-4-enal (4c). Isolated as a nonseparable
mixture of E and Z isomers in 58:42 ratio. Colorless oil. Yield:
0.369 g (94%). HRMS (ESI): m/z 197.1903, [M + H+] (calcd for
C13H25O: 197.1905). NMR data for the E isomer are as follows. H
(E)-2-Methyloct-4-enal (4j).37 Colorless oil. Yield: 0.255 g (91%).
1
3
NMR (C6D6): δ 9.50 (s, 1H, CHO), 5.13−5.06 (m, 1H, CH),
2.31−2.26 (m, 1H, CH), 2.17−1.97 (m, 4H, CH2), 1.56 (br, 3H,
CCH3), 1.44−1.27 (m, 8H, CH2), 0.99−0.94 (m, 6H, CH3) ppm.
13C{1H} NMR (C6D6): δ 202.8 (s, CHO), 137.3 (s, = C), 120.8 (s,
CH), 46.5 (s, CH), 39.7, 31.9, 29.3, 29.0, 27.9, and 22.7 (s, CH2),
23.1 (s, CCH3), 13.9 and 12.7 (s, CH3) ppm. NMR data for the Z
isomer are as follows. 1H NMR (C6D6): δ 9.51 (s, 1H, CHO), 5.13−
5.06 (m, 1H, CH), 2.31−2.26 (m, 1H, CH), 2.17−1.97 (m, 4H,
CH2), 1.70 (br, 3H, CCH3), 1.44−1.27 (m, 8H, CH2), 0.99−0.94
(m, 6H, CH3) ppm. 13C{1H} NMR (C6D6): δ 202.8 (s, CHO), 137.5
(s, = C), 121.4 (s, CH), 46.5 (s, CH), 31.8, 31.7, 28.9, 28.7, 27.9,
and 22.7 (s, CH2), 15.7 (s, CCH3), 13.9 and 12.8 (s, CH3) ppm.
4-Cyclohexylidene-2-methylbutanal (4d).7a Colorless oil. Yield:
1H NMR (C6D6): δ 9.45 (d, 1H, JHH = 1.5 Hz, CHO), 5.46−5.26
(m, 2H, CH), 2.27−2.20 (m, 1H, CH), 2.09−1.90 (m, 4H, 
CCH2), 1.43−1.31 (m, 2H, CH2), 0.94−0.90 (m, 6H, CH3) ppm.
13C{1H} NMR (C6D6): δ 202.9 (s, CHO), 132.9 and 126.7 (s, 
CH), 46.0 (s, CH), 34.6 and 33.6 (s, CCH2), 22.6 (s, CH2), 13.4
and 12.6 (s, CH3) ppm.
(E)-2,3-Dimethylhex-4-enal (4k).13 Isolated as a nonseparable
mixture of syn and anti diastereoisomers in ca. 1:1 ratio. Colorless oil.
Yield: 0.214 g (85%). 1H NMR (C6D6): δ 9.50 and 9.47 (d, 1H, 3JHH
= 1.8 or 2.1 Hz, CHO, syn and anti), 5.44−5.14 (m, 2H, CH, syn
and anti), 2.36−2.30 and 2.10−1.98 (m, 1H, CH, syn and anti),
1.51−1.62 (m, 3H, CCH3, syn and anti), 1.00−0.86 (m, 6H, CH3,
syn and anti) ppm. 13C{1H} NMR (C6D6): δ 203.4 (s, CHO, syn and
anti), 134.1, 133.0, 125.4, and 124.9 (s, CH, syn and anti), 51.2,
50.9, 37.3, and 37.2 (s, CH, syn and anti), 18.1 and 17.6 (s, 
CHCH3, syn and anti), 16.4 (s, CH3, syn and anti), 10.2 and 9.7 (s,
CH3, syn and anti) ppm.
1
3
0.289 g (87%). H NMR (C6D6): δ 9.48 (d, 1H, JHH = 1.2 Hz,
CHO), 5.03 (t, 1H, 3JHH = 7.4 Hz, CH), 2.30−2.22 (m, 1H, CH),
2.14−1.94 (m, 6H, CH2), 1.57−1.43 (m, 6H, CH2), 0.94 (d, 3H, 3JHH
= 8.1 Hz, CH3) ppm. 13C{1H} NMR (C6D6): δ 202.9 (s, CHO),
141.5 (s, C), 117.7 (s, CH), 46.6 (s, CH), 37.2, 28.7 (2C), 28.1,
27.7, and 26.9 (s, CH2), 12.7 (s, CH3) ppm.
ASSOCIATED CONTENT
* Supporting Information
■
2-Methyl-5-phenylhex-4-enal (4e). Isolated as a nonseparable
mixture of E and Z isomers in 72:28 ratio. Colorless oil. Yield: 0.320 g
(85%). HRMS (ESI): m/z 189.1278, [M + H+] (calcd for C13H17O:
189.1279). NMR data for the E isomer are as follows. 1H NMR
(C6D6): δ 9.46 (s, 1H, CHO), 7.38−7.14 (m, 5H, Ph), 5.70−5.66 (m,
1H, CH), 2.40−2.33 (m, 1H, CH), 2.10−2.08 (m, 2H, CH2), 1.91
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00187.
Details of the synthesis and characterization of the diallyl
ethers 3a−l and NMR spectra of the novel diallyl ethers
3a,c,i,k and γ,δ-unsaturated aldehydes 4a,c,e,g (PDF)
3
(s, 3H, CCH3), 0.93 (d, 3H, JHH = 7.2 Hz, CH3) ppm. 13C{1H}
NMR (C6D6): δ 203.0 (s, CHO), 143.7 (s, Cipso), 137.0 (s, C),
128.3 (s, CHmeta), 127.9 (s, CHpara), 125.9 (s, CHortho), 124.5 (s, 
CH), 46.4 (s, CH), 29.6 (s, CH2), 15.8 (s, CCH3), 12.7 (s, CH3)
1
ppm. NMR data for the E isomer are as follows. H NMR (C6D6): δ
AUTHOR INFORMATION
Corresponding Authors
*E-mail for P.C.: crochetpascale@uniovi.es.
*E-mail for V.C.:vcm@uniovi.es.
■
9.32 (s, 1H, CHO), 7.38−7.14 (m, 5H, Ph), 5.36−5.33 (m, 1H, 
CH), 2.28−2.22 (m, 1H, CH), 2.05−1.97 (m, 2H, CH2), 1.99 (s, 3H,
3
CCH3), 0.82 (d, 3H, JHH = 7.2 Hz, CH3) ppm. 13C{1H} NMR
(C6D6): δ 203.1 (s, CHO), 141.8 (s, Cipso), 138.7 (s, C), 128.3 (s,
CHmeta), 126.9 (s, CHpara), 126.8 (s, CHortho), 123.8 (s, CH), 46.5
(s, CH), 29.9 (s, CH2), 25.6 (s, CCH3), 12.8 (s, CH3) ppm.
2,5,9-Trimethyldeca-4,8-dienal (4f).7g Isolated as a nonseparable
mixture of E and Z isomers in 57:43 ratio. Colorless oil. Yield: 0.346 g
(89%). NMR data for the E isomer are as follows. 1H NMR (C6D6): δ
9.48 (d, 1H, 3JHH = 1.5 Hz, CHO), 5.25−5.19 and 5.15−5.07 (m, 1H
each, CH), 2.28−2.00 (m, 7H, CH and CH2), 1.80−1.71 (m, 6H,
CCH3), 1.63 (br, 3H, CCH3), 0.93 (d, 3H, 3JHH = 7.6 Hz, CH3)
ppm. 13C{1H} NMR (C6D6): δ 203.0 (s, CHO), 136.9 and 131.0 (s,
C), 124.4 and 121.1 (s, CH), 46.5 (s, CH), 39.8, 28.9, and 26.7
(s, CH2), 25.5, 23.2, and 17.4 (s, CCH3), 12.7 (s, CH3) ppm. NMR
data for the Z isomer are as follows. 1H NMR (C6D6): δ 9.48 (d, 1H,
3JHH = 1.5 Hz, CHO), 5.25−5.19 and 5.15−5.07 (m, 1H each, 
CH), 2.28−2.00 (m, 7H, CH and CH2), 1.80−1.71 (m, 6H, 
ORCID
Pascale Crochet: 0000-0002-4637-8231
Victorio Cadierno: 0000-0001-6334-2815
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This article is dedicated to Professor Ernesto Carmona, one of
the main contributors to the development of organometallic
chemistry in Spain, on the occasion of his 70th birthday. This
work was supported by the Spanish MINECO (projects
CTQ2013-40591-P and CTQ2016-75986-P) and the Gobier-
no del Principado de Asturias (project GRUPIN14-006). J.F.
thanks MINECO and ESF for the award of a Juan de la Cierva
contract (IJCI-2014-19174).
3
CCH3), 1.56 (br, 3H, CCH3), 0.94 (d, 3H, JHH = 7.6 Hz, CH3)
ppm. 13C{1H} NMR (C6D6): δ 203.0 (s, CHO), 137.1 and 131.3 (s,
C), 124.3 and 121.9 (s, CH), 46.5 (s, CH), 31.9, 28.8, and 26.5
(s, CH2), 25.5, 17.3, and 15.8 (s, CCH3), 12.8 (s, CH3) ppm.
2,3-Dimethyl-3-phenylhex-4-enal (4g). Isolated as a nonseparable
mixture of syn and anti diastereoisomers in ca. 1:1 ratio. Colorless oil.
Yield: 0.380 g (94%). HRMS (ESI): m/z 203.1434, [M + H+] (calcd
REFERENCES
■
(1) Claisen, L. Ber. Dtsch. Chem. Ges. 1912, 45, 3157−3166.
(2) For selected review articles covering Claisen rearrangements,
see: (a) Tarbell, D. S. Chem. Rev. 1940, 27, 495−546. (b) Lutz, R. P.
Chem. Rev. 1984, 84, 205−247. (c) Ziegler, F. E. Chem. Rev. 1988, 88,
1423−1452. (d) Wipf, P. Claisen rearrangements. In Comprehensive
1
for C14H19O: 203.1436). H NMR (C6D6): δ 9.63 and 9.49 (d, 1H,
3JHH = 2.1 or 2.7 Hz, CHO, syn and anti), 7.23−7.08 (m, 5H, Ph),
3
5.41 and 5.30 (d, 1H, JHH = 9.6 Hz, CH, syn and anti), 3.80 and
3.61 (dd, 1H, 3JHH = 3JHH = 9.6 Hz, CH, syn and anti), 2.59−2.53 (m,
́
H
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Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press:
Oxford, U.K., 1991; Vol. 5, pp 827−873. (e) Ganem, B. Angew.
Chem., Int. Ed. Engl. 1996, 35, 936−945. (f) Hiersemann, M.;
Abraham, L. Eur. J. Org. Chem. 2002, 2002, 1461−1471.
(g) Nubbemeyer, U. Synthesis 2003, 2003, 0961−1008. (h) Martin
Castro, A. M. Chem. Rev. 2004, 104, 2939−3002. (i) The Claisen
Rearrangement: Methods and Applications; Hiersemann, M.,
Nubbemeyer, U., Eds.; Wiley-VCH: Weinheim, Germany, 2007.
(j) Majumdar, K. C.; Alam, S.; Chattopadhyay, B. Tetrahedron 2008,
64, 597−643. (k) Martín-Castro, A. M.; Tortosa, M. Claisen
rearrangements. In Comprehensive Organic Synthesis II; Knochel, P.,
Molander, G. A., Eds.; Elsevier: Amsterdam, 2014; Vol. 5, pp 912−
977. (l) Craig, D. The Claisen rearrangement. In Molecular
Rearrangements in Organic Synthesis; Rojas, C. M., Ed.; Wiley:
Hoboken, NJ, 2015; pp 403−430.
(3) See, for example: (a) Grieco, P. A.; Brandes, E. B.; McCann, S.;
Clark, J. D. J. Org. Chem. 1989, 54, 5849−5851. (b) Cramer, C. J.;
Truhlar, D. G. J. Am. Chem. Soc. 1992, 114, 8794−8799.
(c) Severance, D. L.; Jorgensen, W. L. J. Am. Chem. Soc. 1992, 114,
10966−10968. (d) Guest, J. M.; Craw, J. S.; Vincent, M. A.; Hillier, I.
H. J. Chem. Soc., Perkin Trans. 2 1997, 2, 71−74. (e) Gajewski, J. J.
Acc. Chem. Res. 1997, 30, 219−225. (f) Acevedo, O.; Armacost, K. J.
Am. Chem. Soc. 2010, 132, 1966−1975.
(4) See, for example: (a) Hurd, C. D.; Pollack, M. A. J. Am. Chem.
Soc. 1938, 60, 1905−1911. (b) Lorette, N. B.; Howard, W. L. J. Org.
Chem. 1961, 26, 3112−3115. (c) Burrows, C. J.; Carpenter, B. K. J.
Am. Chem. Soc. 1981, 103, 6983−6984.
(5) See, for example: (a) Watanabe, W. H.; Conlon, L. E. J. Am.
Chem. Soc. 1957, 79, 2828−2833. (b) Faulkner, D. J.; Petersen, M. R.
J. Am. Chem. Soc. 1973, 95, 553−563. (c) Nonoshita, K.; Banno, H.;
Maruoka, K.; Yamamoto, H. J. Am. Chem. Soc. 1990, 112, 316−322.
(6) For alternative procedures for the syntheses of allyl vinyl ethers,
most involving transition-metal catalysts and lacking general
application, see ref 2k.
Grayson, M. N.; Goodman, J. M.; Cook, M. J. J. Org. Chem. 2015, 80,
1472−1498.
(13) ICR reactions of allyl homoallyl ethers involving the
isomerization of both CC bonds are also known. See references
7e,g−i and: (a) Higashino, T.; Sakaguchi, S.; Ishii, Y. Org. Lett. 2000,
2, 4193−4195.
(14) See, for example: (a) Aqueous Organometallic Chemistry and
́
́
Catalysis; Horvath, I. T., Joo, F., Eds.; Kluwer Academic: Dordrecht,
The Netherlands, 1995. (b) Aqueous-Phase Organometallic Catalysis;
Cornils, B., Herrmann, W. A., Eds.; Wiley-VCH: Weinheim,
Germany, 2004. (c) Metal-Catalyzed Reactions in Water; Dixneuf, P.
H., Cadierno, V., Eds.; Wiley-VCH: Weinheim, Germany, 2013.
(15) See, for example: (a) Cadierno, V.; García-Garrido, S. E.;
Gimeno, J. Chem. Commun. 2004, 232−233. (b) Cadierno, V.;
Crochet, P.; García-Garrido, S. E.; Gimeno, J. Dalton Trans. 2004,
́
3635−3641. (c) Díaz-Alvarez, A. E.; Crochet, P.; Zablocka, M.;
Duhayon, M.; Cadierno, V.; Gimeno, J.; Majoral, J. P. Adv. Synth.
Catal. 2006, 348, 1671−1679. (d) Cadierno, V.; García-Garrido, S.
́
E.; Gimeno, J.; Varela-Alvarez, A.; Sordo, J. A. J. Am. Chem. Soc. 2006,
́
́
128, 1360−1370. (e) Crochet, P.; Díez, J.; Fernandez-Zumel, M. A.;
Gimeno, J. Adv. Synth. Catal. 2006, 348, 93−100. (f) Cadierno, V.;
Crochet, P.; Francos, J.; García-Garrido, S. E.; Gimeno, J.; Nebra, N.
Green Chem. 2009, 11, 1992−2000. (g) Lastra-Barreira, B.; Díez, J.;
Crochet, P. Green Chem. 2009, 11, 1681−1686. (h) García-Garrido, S.
E.; Francos, J.; Cadierno, V.; Basset, J.-M.; Polshettiwar, V.
ChemSusChem 2011, 4, 104−111.
́
(16) Varela-Alvarez, A.; Sordo, J. A.; Piedra, E.; Nebra, N.; Cadierno,
V.; Gimeno, J. Chem. - Eur. J. 2011, 17, 10583−10599.
(17) (a) Cadierno, V.; García-Garrido, S. E.; Gimeno, J.; Nebra, N.
Chem. Commun. 2005, 4086−4088. (b) Cadierno, V.; Gimeno, J.;
Nebra, N. Chem. - Eur. J. 2007, 13, 6590−6594.
(18) (a) Lastra-Barreira, B.; Crochet, P. Green Chem. 2010, 12,
1311−1314. (b) Lastra-Barreira, B.; Francos, J.; Crochet, P.;
Cadierno, V. Green Chem. 2011, 13, 307−313. (c) Lastra-Barreira,
́
́
(7) (a) Reuter, J. M.; Salomon, R. G. J. Org. Chem. 1977, 42, 3360−
3364. (b) Iyer, R. S.; Kobierski, M. E.; Salomon, R. G. J. Org. Chem.
1994, 59, 6038−6043. (c) Mitchell, T. N.; Gieβelmann, F. Synlett
1996, 1996, 475−476. (d) Schmidt, B.; Wildemann, H. J. Org. Chem.
B.; Díaz-Alvarez, A. E.; Menendez-Rodriguez, L.; Crochet, P. RSC
́
Adv. 2013, 3, 19985−19990. (d) Gamez-Rivera, S. A.; Francos, J.;
Borge, J.; Cadierno, V. Eur. J. Inorg. Chem. 2017, 2017, 4138−4146.
(19) The synthesis of complexes 1b and 2b,d,f has been previously
described in the literature by us and other authors: (a) Miyaki, Y.;
Onishi, T.; Kurosawa, H. Inorg. Chim. Acta 2000, 300−302, 369−377.
(b) Scolaro, C.; Chaplin, A. B.; Hartinger, C. G.; Bergamo, A.;
Cocchietto, M.; Keppler, B. K.; Sava, G.; Dyson, P. J. Dalton Trans.
2007, 5065−5072. (c) Lastra-Barreira, B.; Díez, J.; Crochet, P.;
̂
́
2000, 65, 5817−5822. (e) Le Notre, J.; Brissieux, L.; Semeril, D.;
Bruneau, C.; Dixneuf, P. H. Chem. Commun. 2002, 1772−1773.
̂
(f) Ben Ammar, H.; Le Notre, J.; Salem, M.; Kaddachi, M. T.;
Dixneuf, P. H. J. Organomet. Chem. 2002, 662, 63−69. (g) Ben
Ammar, H.; Le Notre, J.; Salem, M.; Kaddachi, M. T.; Toupet, L.;
̂
́
Renaud, J.-L.; Bruneau, C.; Dixneuf, P. H. Eur. J. Inorg. Chem. 2003,
Fernandez, I. Dalton Trans. 2013, 42, 5412−5420.
2003, 4055−4064. (h) Schmidt, B. Synlett 2004, 1541−1544. (i) Le
(20) (a) Although the ability of these species to promote olefin
isomerization reactions was not previously evaluated, their structural
similarity with compounds [RuCl2(η6-C6H5OCH2CH2OH)(PR3)]
made us presage a good catalytic behavior, since the latter were found
to be extremely active in the isomerization of allylic alcohols and
allylbenzenes in water (see refs 15g and 18a,c). (b) On the other
hand, we must note that catalytic systems based on arene-
ruthenium(II) complexes for ICR reactions in organic media were
described by Dixneuf and co-workers (see refs 7e−g,i).
̂
Notre, J.; Touzani, R.; Lavastre, O.; Bruneau, C.; Dixneuf, P. H. Adv.
Synth. Catal. 2005, 347, 783−791. (j) Schmidt, B.; Nave, S. J. Org.
Chem. 2006, 71, 7364−7369.
(8) (a) Swenton, J. S.; Bradin, D.; Gates, B. D. J. Org. Chem. 1991,
56, 6156−6163. (b) Nelson, S. G.; Bungard, C. J.; Wang, K. J. Am.
Chem. Soc. 2003, 125, 13000−13001. (c) Stevens, B. D.; Nelson, S. G.
J. Org. Chem. 2005, 70, 4375−4379. (d) Nelson, S. G.; Wang. J. Am.
Chem. Soc. 2006, 128, 4232−4233. (e) Trost, B. M.; Zhang, T. Org.
Lett. 2006, 8, 6007−6010. (f) Stevens, B. D.; Bungard, C. J.; Nelson,
S. G. J. Org. Chem. 2006, 71, 6397−6402. (g) Wang, K.; Bungard, C.
J.; Nelson, S. G. Org. Lett. 2007, 9, 2325−2328. (h) McLaughlin, M.
G.; Cook, M. J. J. Org. Chem. 2012, 77, 2058−2063. (i) Sulake, R. S.;
Chen, C. Org. Lett. 2015, 17, 1138−1141.
(21) Within the series, compounds 3a,c,i,k have not been previously
described in the literature.
(22) All attempts to separate the E and Z isomers of aldehyde 4a by
column chromatography failed; therefore, they were jointly
1
characterized. Unfortunately, most signals in the H NMR spectrum
(9) (a) Stork, G.; Atwal, K. S. Tetrahedron Lett. 1982, 23, 2073−
2076. (b) Nevado, C.; Echavarren, A. M. Tetrahedron 2004, 60,
9735−9744.
were overlapped, thus preventing the carrying out of conclusive
NOESY experiments to unambiguously determine the stereo-
chemistry of the major isomer. However, given the stereoselectivity
usually found in aliphatic Claisen rearrangements (see ref 2), we
assumed that the E stereoisomer is the major species.
(23) Crochet, P.; Cadierno, V. Dalton Trans. 2014, 43, 12447−
12462.
(10) (a) Miller, S. P.; Morken, J. P. Org. Lett. 2002, 4, 2743−2745.
(b) Okamoto, R.; Tanaka, K. Org. Lett. 2013, 15, 2112−2115.
(11) The combined use of iridium and palladium catalysts has also
been described: Kerrigan, N. J.; Bungard, C. J.; Nelson, S. G.
Tetrahedron 2008, 64, 6863−6869.
(24) Miyaki, Y.; Onishi, T.; Ogoshi, S.; Kurosawa, H. J. Organomet.
Chem. 2000, 616, 135−139.
(12) Cook and co-workers demonstrated very recently that ICR
reactions of aryl-substituted diallyl ethers can also be promoted by
potassium tert-butoxide: Reid, J. P.; McAdam, C. A.; Johnston, A. J. S.;
(25) (a) The low solubility in water of complex 5 is most likely
−
related to the SbF6 counteranion. Unfortunately, all attempts made
I
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Article
to synthesize analogous species with more solubilizing counteranions
(AcO− or TfO−) in a pure manner failed. (b) On the other hand, the
catalytic behavior of the precursor complexes [{RuCl(μ-Cl)(η6-
C 6 H 5 C H 2 C H 2 O H ) } 2
]
a n d [ R u C l 2 { η 6 : κ 1 ( O ) -
C6H5CH2CH2CH2OH}] was also evaluated, leading to very low
conversions after 6 h (up to 31%).
(26) The equilibrium could be shifted toward the formation of
cationic complexes [RuCl(H2O)(η6-C6H5CH2CH2CH2OH)(PR3)]
[Cl] and [RuCl(η6:κ1(O)-C6H5CH2CH2CH2OH)(PR3)][Cl] by
addition of a silver salt (e.g., AgNO3). On the other hand, the
dichloride derivative [RuCl2(η6-C6H5CH2CH2CH2OH)(PR3)] is the
only product observed by NMR in aqueous NaCl solutions.
(27) All attempts to isolate and fully characterize these species failed.
(28) The complex [Ru(H2O)(OH)(η6-C6H5CH2CH2CH2OH)
(PMe3)][Cl] is probably in rapid equilibrium (on the NMR time
scale) with [Ru(OH)2(η6-C6H5CH2CH2CH2OH)(PMe3)] and
[Ru(H2O)2(η6-C6H5CH2CH2CH2OH)(PMe3)][Cl]2. Similarly,
[Ru(OH)(η6:κ1(O)-C6H5CH2CH2CH2OH)(PMe3)][Cl] should be
in equilibrium with [Ru(H2O)(η6:κ1(O)-C6H5CH2CH2CH2O)
(PMe3)][Cl], [Ru(OH)(η6:κ1(O)-C6H5CH2CH2CH2O)(PMe3)],
and [Ru(H2O)(η6:κ1(O)-C6H5CH2CH2CH2OH)(PMe3)][Cl]2. For
similar processes see, for example: Gossens, C.; Dorcier, A.; Dyson, P.
J.; Rothlisberger, U. Organometallics 2007, 26, 3969−3975.
(29) The transformation of P(OMe)3 into P(OMe)2OH was
evidenced by NMR spectroscopy by a change of the chemical shift
of the phosphorus nucleus from ca. 121 ppm to ca. 100 ppm, as well
as by the decrease of the relative integration for the Me units in the
1H NMR spectrum (from 9H to 6H).
(30) Ruthenium complexes containing ligands functionalized with
basic groups are known to favor CC bond migrations through
bifunctional catalysis mechanisms related to that proposed in Scheme
6. See, for example: Grotjahn, D. D.; Larsen, C. R.; Gustafson, J. L.;
Nair, R.; Sharma, A. J. Am. Chem. Soc. 2007, 129, 9592−9593.
(31) As in the case of 4a, the overlapping of signals in the 1H NMR
of 4c,f did not allow us to carry out conclusive NOESY experiments
to confirm in an unequivocal manner the E stereochemistry proposed
for the major isomer. Fortunately, this was possible for 4e, the
NOESY spectrum showing for the major stereoisomer a positive NOE
effect between the olefinic and aromatic protons in agreement with
the E stereochemistry proposed (for the minor isomer the expected
spatial proximity between the olefinic proton and the methyl group
was also evidenced by the NOESY experiments).
(32) In most classical mechanisms for metal-catalyzed olefin
isomerization, i.e. “allyl-hydride” and “metal-alkyl”, coordination of
the carbon−carbon double bond to the metal is an essential
requirement. See, for example: (a) Parshall, G. W.; Ittel, S. D. In
Homogeneous Catalysis; Wiley: New York, 1992; pp 9−24.
(b) Herrmann, W. A. In Applied Homogeneous Catalysis with
Organometallic Compounds; Cornils, B., Herrmann, W. A., Eds.;
Wiley-VCH: Weinheim, Germany, 1996; Vol. 2, pp 980−991.
(33) Armarego, W. L. F.; Chai, C. L. L. Purification of Laboratory
Chemicals, 5th ed.; Butterworth-Heinemann: Oxford, U.K., 2003.
(34) (a) Ohnishi, T.; Miyaki, Y.; Asano, H.; Kurosawa, H. Chem.
̌
Lett. 1999, 28, 809−810. (b) Cubrilo, J.; Hartenbach, I.; Schleid, T.;
Winter, R. F. Z. Anorg. Allg. Chem. 2006, 632, 400−408.
(35) Although this complex was initially formulated by Kurosawa
and co-workers (see ref 19a) as a chloride-bridged dimer, i.e.
[{RuCl(μ-Cl)(η6-C6H5CH2CH2CH2OH)}2], X-ray diffraction studies
carried out later evidenced its monomeric tethered structure (see ref
34b).
(36) Although compound 4a was mentioned in a patent, no
characterization data were provided: Henrick, C. A. Diolefinic
aliphatic compounds. Fr. Demande FR2124279, 1972.
(37) Park, S.-A.; Chung, I.-M.; Ahmad, A. J. Essent. Oil-Bear. Plants
2012, 15, 858−863.
J
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