Investigation and mechanistic study into intramolecular hydroalkoxylation of unactivated alkenols catalyzed by cationic lanthanide complexes

Article abstract of DOI:10.1016/j.tet.2017.01.051

Cationic lanthanide complexes of the type [Ln(CH₃CN)₉]³⁺[(AlCl₄)₃]^3–·CH₃CN (Ln = Pr, Nd, Sm, Gd, Er, Yb, Y) served as effective catalysts for the intramolecular hydroalkoxylation/cyclization of unactivated alkenols to yield the cyclic ethers with Markovnikov regioselectivity under mild conditions. Novel cationic complexes, [AlCl(CH₃CN)₅]²⁺[(AlCl₄)₂]^2–·CH₃CN and [Nd(CH₃CN)₉]³⁺[(FeCl₄)₃]^3–·CH₃CN, were synthesized and evaluated for the intramolecular hydroalkoxylation/cyclization of unactivated alkenols for comparison. The active sequence of [Nd(CH₃CN)₉]³⁺[(FeCl₄)₃]^3–·CH₃CN < [AlCl(CH₃CN)₅]²⁺[(AlCl₄)₂]^2–·CH₃CN < [Nd(CH₃CN)₉]³⁺[(AlCl₄)₃]^3–·CH₃CN observed indicated that both the cation and anion have great influence on the activity. Comparative study on the activity of AlCl₃and its cationic complex [AlCl(CH₃CN)₅]²⁺[(AlCl₄)₂]^2–·CH₃CN revealed the formation of the cationic Al center enhanced the activity greatly. The¹H NMR studies indicated the activation of hydroxyl and olefin by the cationic Ln³⁺center were involved in the reaction pathways.

Full text of DOI:10.1016/j.tet.2017.01.051

Accepted Manuscript
Investigation and mechanistic study into intramolecular hydroalkoxylation of
unactivated alkenols catalyzed by cationic lanthanide complexes
Xuehua Zhu, Guoyao Li, Fan Xu, Yong Zhang, Mingqiang Xue, Qi Shen
PII:
S0040-4020(17)30086-8
10.1016/j.tet.2017.01.051
TET 28421
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 13 November 2016
Revised Date: 16 January 2017
Accepted Date: 23 January 2017
Please cite this article as: Zhu X, Li G, Xu F, Zhang Y, Xue M, Shen Q, Investigation and mechanistic
study into intramolecular hydroalkoxylation of unactivated alkenols catalyzed by cationic lanthanide
complexes, Tetrahedron (2017), doi: 10.1016/j.tet.2017.01.051.
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IntramolecularHydroalkoxylation of Unactivated
Alkenols Catalyzed by Cationic Lanthanide Complexes
†
,
‡
†
,
†
Xuehua Zhu, Guoyao Li, Fan Xu,* Yong
†
†
,
†
Zhang, Mingqiang Xue, Qi Shen*
†
College of Chemistry, Chemical Engineering and Materials Science
Soochow University, Suzhou 215123, People’s Republic of China
School of chemical biology and materials engineering
‡
Suzhou University of Science and Technology, Suzhou 215009, People’s Republic of China

ACCEPTED MANUSCRIPT
Investigation and Mechanistic Study into Intramolecular
Hydroalkoxylation of Unactivated Alkenols Catalyzed by Cationic
Lanthanide Complexes
†
,
‡
†
,
†
†
†
,
†
Xuehua Zhu,
Guoyao Li, Fan Xu,* Yong Zhang, Mingqiang Xue, Qi Shen*
†
College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123,
People’s Republic of China
‡
School of chemical biology and materials engineering, Suzhou University of Science and Technology, Suzhou
2
15009, People’s Republic of China
qshen@suda.edu.cn; xufan@suda.edu.cn
3+
3–
Abstract: Cationic lanthanide complexes of the type [Ln(CH CN) ] [(AlCl ) ] •CH CN (Ln = Pr,
3
9
4 3
3
Nd, Sm, Gd, Er, Yb, Y) served as effective catalysts for the intramolecular
hydroalkoxylation/cyclization of unactivated alkenols to yield the cyclic ethers with Markovnikov
regioselectivity
under
mild
conditions.
Novel
cationic
complexes,
2+
2–
3+
3–
[
AlCl(CH CN) ] [(AlCl ) ] •CH CN and [Nd(CH CN) ] [(FeCl ) ] •CH CN, were synthesized and
3 5 4 2 3 3 9 4 3 3
evaluated for the intramolecular hydroalkoxylation/cyclization of unactivated alkenols for
3+
3–
comparison.
The
active
sequence
of
[Nd(CH CN) ] [(FeCl ) ] •CH CN
<
3
9
4 3
3
2+
2–
3+
3–
[
AlCl(CH CN) ] [(AlCl ) ] •CH CN < [Nd(CH CN) ] [(AlCl ) ] •CH CN observed indicated that
3 5 4 2 3 3 9 4 3 3
both the cation and anion have great influence on the activity. Comparative study on the activity of
2+
2–
AlCl and its cationic complex [AlCl(CH CN) ] [(AlCl ) ] •CH CN revealed the formation of the
3
3
5
4 2
3
1
cationic Al center enhanced the activity greatly. The H NMR studies indicated the activation of
3+
hydroxyl and olefin by the cationic Ln center were involved in the reaction pathways.
Keywords: alkenol, hydroalkoxylation, cationic lanthanide complex, reaction mechanism,
catalysis
1. Introduction
Saturated oxygen heterocycles are recognized as important structural moieties that are found
in a wide range of naturally occurring and biologically active molecules, such as polyethers,
1

ACCEPTED MANUSCRIPT
1
antibiotics, acetogenins and prostaglandins. Intramolecular addition of an O-H bond across an
unsaturated C-C bond of a pendant olefin (intramolecular hydroalkoxylation) is an
atom-economical, and therefore particularly attractive, approach for preparing saturated oxygen
heterocycles. The hydroalkoxylation of alkenols traditionally involves reaction with a stoichiometric
2
amount of a toxic metal ion, followed by reduction. Catalytic processes for such transformations
3
4
are limited, particularly for unactivated alkenols. Brønsted acids, transition metals salts such as
4a
4b
4c,4d,4h
4e
5
those of gold, tin, ruthenium,
and platinum, and some metal triflates have been
reported as effective catalysts for intramolecular and intermolecular hydroalkoxylation of olefins.
However, these transition metal catalysts are either toxic or relatively expensive. Therefore, the
development of new, efficient and cheaper methods for intramolecular and intermolecular
6
hydroalkoxylation of olefins has attracted great attention. Recently, Marks et al. reported that
homoleptic lanthanide amido complexes (Ln[N(SiMe ) ] ) are effective and selective precatalysts
3
2 3
for the intramolecular hydroalkoxylation/cyclization of alkynyl and allenyl alcohols providing
7
exocyclic enol ethers. Lanthanide triflates (Ln(OTf) ) also serve as efficient catalysts for the
3
intramolecular hydroalkoxylation/cyclization of primary or secondary, and aliphatic or aromatic
hydroxyalkenes at room temperature in ionic liquids, affording five- and six-membered oxygen
8
heterocycles with Markovnikov-type selectivity.
Cationic metal species are generally more electrophilic than their neutral forms, and thus are
more active homogeneous catalysts. Cationic lanthanide alkyl complexes are well known to be
more active and selective in catalyzing olefin polymerization and copolymerization with respect to
9
their neutral analogs. However, the use of cationic lanthanide complexes in organic
10
transformations remains limited, and examples include intramolecular hydroamination,
11
12
dimerization of phenylacetylene and hetero-Diels-Alder reaction.
We previously reported that anhydrous lanthanide trichlorides (LnCl ) react easily with
3
anhydrous AlCl in acetonitrile (CH CN), affording disconnected ion-pair Ln/Al complexes,
3
3
3+
3–
13
[
Ln(CH CN) ] [(AlCl ) ] •CH CN, in almost quantitative yields. The lanthanide ions in these
3 9 4 3 3
cationic complexes exhibit high electrophilicity and therefore can act as catalysts for styrene
14
polymerization without the need for a co-catalyst. These studies led us to investigate the
intramolecular hydroalkoxylation of unactivated alkenols using these complexes as catalysts, with
the aim of expanding the scope of cationic lanthanide complexes in organic synthesis. It was found
that these complexes show good activity for a wide range of substrates, and we now disclose
2

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these results. The syntheses and molecular structures of novel cationic complexes,
2+
2–
3+
3–
[
AlCl(CH CN) ] [(AlCl ) ] •CH CN and [Nd(CH CN) ] [(FeCl ) ] •CH CN, and investigation of
3 5 4 2 3 3 9 4 3 3
their catalytic activity in the intramolecular hydroalkoxylation of alkenols were studied to assess
the influence of both the cation and the counteranion on the activity of this type of complex.
2. Results and Discussion
2
.1 Optimization of the intramolecular hydroalkoxylation
3+
3–
2
.1.1 Syntheses of [Ln(CH CN) ] [(AlCl ) ] •CH CN (Ln= Pr I, Nd II, Sm III, Gd IV, Er V, Yb VI
3 9 4 3 3
and Y VII) and the molecular structures of the Nd and Y complexes. A series of cationic complexes,
3+
3–
[
Ln(CH CN) ] [(AlCl ) ] •CH CN, containing the early to later lanthanide metals were
3 9 4 3 3
synthesized by the reaction of LnCl and AlCl in CH CN according to a reported procedure
3
3
3
13
(Scheme 1).
3+
3–
Scheme 1. Syntheses of [Ln(CH CN) ] [(AlCl ) ] •CH CN
3
9
4 3
3
3+
3–
The solid state structures of
the [Nd(CH CN) ] [(AlCl ) ] •CH CN II and
3 9 4 3 3
3+
3–
[
Y(CH CN) ] [(AlCl ) ] •CH CN VII complexes were determined by X-ray crystal structural
3 9 4 3 3
15
analysis, as they were unknown in the literature. They are isostructural and isomorphous, and
13
their molecular structures are similar to that of the analogous Sm complex reported previously.
3+
Both have an ion-pair structure consisting of one cation [Ln(CH CN) ] and three anions of
3
9
–
(
AlCl ) (See Supplementary data).
4
2
.1.2 Solvent effects on the catalytic intramolecular hydroalkoxylation/cyclization of alkenols. The
intramolecular hydroalkoxylation/cyclizations of aromatic alkenol 1a and aliphatic alkenol 1b were
investigated as model reactions, using 5 mol% of II in CHCl at 65 °C for 1a, and in DCE at 83 °C
3
3+
3–
for 1b. We were pleased to observe that the [Nd(CH CN) ] [(AlCl ) ] •CH CN complex exhibited
3
9
4 3
3
high catalytic activity in both reactions, affording 95% conversion of 1a to cyclic ether 2a (Table 1,
entry 1), and 93% yield of cyclic ether 2b (Table 2, entry 1) after 24 h. These encouraging results
led us to examine the reactions further in various solvents. Thus, DCE, CHCl and CH CN for the
3
3
3

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reaction of 1a, and CHCl , DCE, CH NO and toluene for the reaction of 1b were investigated with
3
3
2
a 5 mol% catalyst loading at different temperatures. The choice of solvent appeared to have a
noticeable effect on both reactions. The hydroalkoxylation/cyclization reactions of 1a in CHCl at
3
6
5 °C and in DCE at 83 °C were almost complete after 24 h, affording 2a in 95% and 90% yield,
respectively (Table 1, entries 1 and 2). However, only a trace of 2a was obtained when the reaction
was carried out in CH CN (Table 1, entry 3). Moreover, whereas reaction of unsaturated alcohol 1b
3
gave an almost quantitative yield of cyclic ether 2b in DCE at 83 °C (93% yield, Table 2, entry 1),
only 88% and 80% conversion of 1b to 2b was achieved when using toluene at 110 °C and
CH NO at 100 °C , respectively (Table 2, entries 2 and 4). Only a 50% yield of 2b was obtained in
3
2
CHCl at 65 °C (Table 2, entry 3). Thus, the optimal solv ent for this system is CHCl for aromatic
3
3
hydroxyalkenes, and DCE for aliphatic hydroxyalkenes.
The reaction concentration also affects the yield of the reaction. As illustrated in Table 1, the
yield of 2a decreased with an increase in the concentration of 1a in a range from 0.5–2.0 mol/L
(Table 1, entries 1, 4 and 5). The lowest-yielding reaction of 2a was under solvent-free conditions
(49%, Table 1, entry 6). This may be attributed to the poor solubility of the catalyst both in the
substrate and the resulting product.
.1.3 Lanthanide metal effects on catalytic intramolecular hydroalkoxylation/cyclization of alkenols.
2
The influence of the lanthanide metal (Ln) on the model reactions of 1a and 1b was then screened
in CHCl at 65 °C for the former (Table 1), and in DCE at 83 °C for the latter (Table 2). As shown in
3
3+
3–
Table 1, the activity of the complexes [Ln(CH CN) ] [(AlCl ) ] •CH CN increases substantially
3
9
4 3
3
with a decrease in the Ln ionic radius. The reaction using the smallest ionic radius catalyst (Yb)
afforded a quantitative yield of 2a, medium-sized Ln catalysts (Sm and Gd) afforded 87–88%
yields of 2a, and 81–82% yields were achieved for the larger Nd and Pr metal catalysts (Table 1,
entries 7–10 and 12). The activity of the Y complex is somewhat lower than that of the Yb complex
(Table 1, entry 11). The sequence of Pr~Nd<Sm~Gd<Y<Yb observed here is consistent with an
increasing trend of Lewis acidity of the Ln ions. This pattern parallels that of
16
organolanthanide-catalyzed aminoalkyne hydroamination/cyclizations, and Ln(OTf) -catalyzed
3
8
hydroxyalkene hydroalkoxylation/cyclizations, but not that of organolanthanide-catalyzed
17
aminoalkene hydroamination/cyclizations, or organolanthanide-catalyzed hydroxyalkyne and
7c,18
hydroxyallene hydroalkoxylation/cyclizations.
It is noteworthy that the complex VI showed a high activity in this transformation. The reaction
4

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using 1.0 mol% of VI in CHCl at 65 °C afforded a complete conversion of 1a to 2a after 24 h, and a
3
9
3% conversion after 18 h (Table 1, entries 13 and 14). The same reaction afforded 2a in 81%
yield after 24 h, even with a lower catalyst loading of 0.5 mol% (Table 1, entry 15).
An increasing activity with increasing Ln ionic radius was observed for the reaction of 1b
(Table 2, entries 5–11). The sequence of Yb<Y~Er~Gd<Sm~Nd~Pr here is in contrast to that
found for the reaction of 1a. The reason for such a substrate-dependent Ln metal effect is not clear,
but the same outcome was also observed in the hydroalkoxylation/cyclization of unactivated
8
alkenols catalyzed by Ln(OTf)3.
3+
3–
Table 1 Screening of [Ln(CH CN) ] [(AlCl ) ] •CH CN complexes and solvents for
3
9
4 3
3
a
intramolecular hydroalkoxylation/cyclization of 1a
Entry
1
Ln catalyst (loading, mol%)
Solvent
CHCl3
DCE
GC yield (%)
II (5.0)
II (5.0)
II (5.0)
II (5.0)
II (5.0)
II (5.0)
I (2.5)
95
90
8
b
2
b
3
CH CN
3
c
4
CHCl3
CHCl3
-
80
73
49
81
82
87
d
5
e
6
7
8
9
CHCl3
CHCl3
CHCl3
II (2.5)
III (2.5)
5

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1
0
IV (2.5)
VII (2.5)
VI (2.5)
VI (1.0)
VI (1.0)
VI (0.5)
CHCl
88
3
11
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
95
1
1
1
2
3
4
5
>99
>99
f
93
1
81
a
b
c
Reactions were conducted with 1 mmol of substrate in 2 mL of solvent at 65 °C for 24 h. At 83 °C . The
d
e
f
concentration of substrate was 1 mol/L. The concentration of substrate was 2 mol/L. Solvent free. 18 h.
3+
3–
Table 2 Screening of [Ln(CH CN) ] [(AlCl ) ] •CH CN complexes and solvents for
3
9
4 3
3
a
intramolecular hydroalkoxylation/cyclization of 1b
Entry
Ln catalyst (loading, mol%)
Solvent
DCE
Temp. ( °C )
GC yield (%)
1
2
3
4
5
6
II (5.0)
II (5.0)
II (5.0)
II (5.0)
II (2.5)
I (2.5)
83
93
88
50
80
90
91
toluene
CHCl3
110
65
CH NO2
100
83
3
DCE
DCE
83
6

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7
8
9
1
III (2.5)
IV (2.5)
V(2.5)
DCE
83
83
83
83
83
91
36
40
39
31
DCE
DCE
DCE
DCE
0
VII (2.5)
VI (2.5)
11
a
Reactions were conducted with 1 mmol of substrate in 2 mL of solvent for 24 h.
2
.2 Scope of the catalytic intramolecular hydroalkoxylation/cyclization of alkenols
To probe the scope of the present catalytic hydroalkoxylation/cyclization process, the complex
II (2.5 mol%) was chosen as the catalyst for the reactions of aliphatic hydroxyalkenes, and the
complex VI (1 mol%) was used for the aromatic hydroxyalkenes. The reaction solvent and
temperature were selected based on the substrates used (DCE, 83 °C for aliphatic hydroxyalkenes;
CHCl , 65 °C for aromatic hydroxyalkenes). From the resul ts in Table 3 it can be seen that
3
3+
3–
[
Ln(CH CN) ] [(AlCl ) ] •CH CN complexes serve as robust and effective catalysts for the
3 9 4 3 3
hydroalkoxylation/cyclization of both aromatic and aliphatic hydroxyalkenes. The
hydroalkoxylation/cyclization of hydroxyalkenes with a terminal double bond (1b, 1d, 1f, 1i, and 1j)
proceeded smoothly to give the corresponding products in good to excellent yields (Table 3,
entries 1, 3, 5, 8 and 9), except for 1g. The ring-size dependence of the reaction activity on the
substrates used here is 5>6, which is consistent with a sterically controlled ring-forming transition
8
state, and is also observed for the other reported catalysts (Table 3, entries 1 vs. 3, 5 vs. 6, and 8
vs. 7). The reactions of the unsaturated alcohols with a disubstituted terminal double bond, such
as 1e and 1h, led exclusively to the formation of the corresponding tetrahydropyrans 2e and 2h
(Table 3, entries 4 and 7), and no five-membered cyclic ether was observed. This indicates that the
present hydroalkoxylation/cyclization proceeds at the more substituted carbon atom of the double
bond with Markovnikov selectivity. This is similar to those found with the reported lanthanide (La,
8
4,5b
Sm, Yb), aluminum, and other transition metal catalysts . In the case of an alcohol such as 1c,
7

ACCEPTED MANUSCRIPT
the cyclization was successful in refluxing DCE, regiospecifically affording the five-membered
cyclic ether as the only product in quantitative yield (Table 3, entry 2). The intramolecular addition
of the hydroxyl group to a cyclohexene also works, such as the reaction with 1k, although the yield
of the cyclic ether 2k was somewhat low (Table 3, entry 10).
3+
3–
The
[Ln(CH CN) ] [(AlCl ) ] •CH CN
catalysts
are
also
efficient
in
the
3
9
4 3
3
hydroalkoxylation/cyclization of aromatic hydroxyalkenes such as 1a, 1l, 1m, 1n, 1o and 1p. The
present cyclization tolerated a number of functional groups at the phenyl ring including Me, MeO,
Cl, and Br (Table 3, entries 13–16). The activity of the hydroxyalkenes with an
electron-withdrawing group para to the hydroxyl (Table 3, entries 15 and 16) is higher than that of
those with an electron-donating group at the same position (Table 3, entries 13 and 14). The
3+
3–
efficiency of the [Ln(CH CN) ] [(AlCl ) ] •CH CN-catalyzed hydroalkoxylation/cyclization of
3
9
4 3
3
aromatic hydroxyalkenes was sensitive to the group at the ortho position to the hydroxyl. For
example, 1a underwent cyclization in almost quantitative yield, but 1l only afforded a moderate
yield of the desired product (Table 3, entries 11 and 12). This may be due to the bulky group
preventing the coordination of the hydroxyl group to the central metal atom.
Table 3. Intramolecular hydroalkoxylation/cyclization of aliphatic and aromatic alkenols
3+
3–
a
catalyzed by [Ln(CH CN) ] [(AlCl ) ] •CH CN
3
9
4 3
3
Entry
Substrate
Product
GC yield (%)
90
1
1b
2
b
2
3
>99
85
1
c
2
c
1d
2
d
b
4
5
97/50
1
e
2
e
b
98/85
1
f
2
f
6
7
60
91
1
g
2
g
1
h
2
h
8

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b
b
8
9
98/87
81/75
1
1
i
j
2
i
O
2
j
c
1
0
49
1
k
2k
d
b
1
1
>99/97
55
2
2
2
a
l
1
a
e
e
1
1
2
3
1
l
b
87/81
m
1
m
e
e
b
1
1
4
5
81/76
2
n
1
n
o
p
b
95/89
2
o
p
1
e
b
1
6
99/97
2
1
a
Reactions were conducted with 1 mmol of substrate in 2 mL of DCE for 24 h catalyzed
b
c
d
e
by 2.5 mol% II at 83 °C . Isolated yield. 48 h. 1 mol% VI, CHCl , 65 °C . 2.5 mol% VI,
3
CHCl , 65 °C .
3
2
.3 Mechanistic study
To gain information on the true catalytic species, the hydroalkoxylation/cyclization reactions of
a catalyzed by anhydrous YbCl (1 mol%), AlCl (3 mol%) and a mixture of YbCl (1 mol%) and
1
3
3
3
AlCl (3 mol%) were conducted in CHCl at 65 °C as control experiments. The results are
3
3
9

ACCEPTED MANUSCRIPT
summarized in Table 4.
a
Table 4. Screening of YbCl and AlCl for the intramolecular hydroalkoxylation/cyclization of 1a
3
3
Entry
Catalyst (loading, mol%)
GC yield (%)
1
2
3
YbCl (1.0)
trace
30
3
AlCl (3.0)
3
YbCl (1.0) + AlCl (3.0)
31
3
3
b
4
CH CN–treated YbCl (1.0)
trace
69
3
3
b
5
CH CN–treated AlCl (3.0)
3 3
a
b
Reactions were carried out at 65 °C in CHCl 3 for 24 h, the substrate concentration was 0.5 mol/L. The
catalyst was first treated with CH CN at room temperature for 24 h, then evaporated to dry to catalyze the
3
hydroalkoxylation/cyclization of 1a.
Anhydrous YbCl alone was almost completely inactive in this transformation, and only a trace
3
of 2a was detected (Table 4, entry 1) under the same reaction conditions as those used for VI
(
Table 1, entry 13). Anhydrous AlCl was also an inefficient catalyst, and the reaction using 3 mol%
3
AlCl in CHCl afforded only a 30% yield of 2a after 24 h (Table 4, entry 2). The reaction with a
3
3
mixture of YbCl and AlCl as the catalyst afforded a 31% yield of 2a (Table 4, entry 3), which is
3
3
probably due to the accumulation of the catalytic activities of the individual YbCl and AlCl species.
3
3
The much higher activity exhibited by VI (>99% yield of 2a, Table 1, entry 13) compared with that
of the mixture of YbCl and AlCl demonstrates that the cationic complex did not decompose into a
3
3
mixture of YbCl and AlCl during the reaction process. Indeed, VI is stable in the CHCl solution of
3
3
3
the phenol. After stirring a 1:1 mixture of VI and phenol in CHCl for 24 h, the complex VI was
3
recovered. Thus, the cationic complex VI itself may be the true catalyst for the present
hydroalkoxylation/cyclization. Also, the much higher activity of the complex VI compared with that
of YbCl may be attributed to the formation of the more electrophilic cationic Yb metal species.
3
1
0

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2
.3.1 Influence of the cation on the activity. It is noteworthy that the yield of 2a increased from 30%
to 69% when the AlCl was first treated with CH CN at room temperature for 24 h, then evaporated
3
3
to dryness (Table 4, entry 5). Conversely, no difference in the yield of 2a was observed when the
CH CN-treated YbCl was used instead of the untreated YbCl (Table 4, entry 4). To understand
3
3
3
the reason for such a great difference in reaction with the CH CN-treated AlCl , the reaction of
3
3
AlCl with CH CN at room temperature was investigated in detail. Stirring a suspension of AlCl in
3
3
3
CH CN for 24 h afforded a clean, colorless solution. Concentrating the solution and crystallizing
3
from a mixed solvent of CH CN and hexane at room temperature led to the formation of colorless
3
crystals in almost quantitative yield. X-ray crystal structural analysis revealed that the crystals are
2+
2–
the cationic Al complex [AlCl(CH CN) ] [(AlCl ) ] •CH CN VIII, which is composed of one cation
3
5
4 2
3
2+
–
19
[
AlCl(CH CN) ] and two anions (AlCl ) (Scheme 2). The molecular structure of VIII is shown in
3 5 4
Figure 1. The Al atom in the cation bonds to one Cl atom and five CH CN molecules in a distorted
3
octahedral geometry.
Scheme 2. Synthesis of VIII
Figure 1. Molecular structure of VIII.
1
1

ACCEPTED MANUSCRIPT
The complex VIII was then evaluated in the intramolecular hydroalkoxylation/cyclization of
unactivated alkenols. As shown in Table 5, the reaction of 1a with 1 mol% VIII in CHCl at 65°C
3
yielded 2a in 69% yield after 24 h (Table 5, entry 5). This is the same yield obtained with the
CH CN-treated AlCl (Table 4, entry 5), indicating that the formation of a cationic Al species leads
3
3
to a large increase in activity. The yield of 2a could be increased to 90% when the catalyst loading
was increased to 5 mol% (Table 5, entry 5). Table 5 shows that VIII can serve as a catalyst for the
transformation of unactivated alkenols to cyclic ethers; however, the activity is much lower than
3+
3–
that of the [Ln(CH CN) ] [(AlCl ) ] •CH CN complexes. Moreover, the efficiency of the
3
9
4 3
3
hydroalkoxylation/cyclization with VIII was very sensitive to the substrates used (Table 5, entries 3,
4
and
6).
Comparing
results
between
the
two
cationic
complexes,
3+
3–
[
Ln(CH CN) ] [(AlCl ) ] •CH CN and VIII, demonstrates that the cation plays an important role in
3 9 4 3 3
determining the efficiency of the complex.
a
Table 5. Intramolecular hydroalkoxylation of alkenols catalyzed by VIII
Entry
1
Substrate
Product
GC yield (%)
b
71/61
1
1
b
f
2
b
2
3
4
72
33
2.7
2
f
1
g
2
2
g
h
1
h
c
b
d
5
90 /69
2
a
1
a
c
6
38
1
l
2l
a
Reactions were catalyzed by 10 mol% VIII at 83 °C in DCE for 24 h, the substrate
b
c
concentration was 0.5 mol/L. Catalyst loading 5 mol%. Solvent CHCl , reaction
3
d
temperature 65 °C . Catalyst loading 1 mol%.
2
.3.2 Influence of the anion on the activity. A novel cationic Nd/Fe complex
1
2

3+
3–
ACCEPTED MANUSCRIPT
2
0
[
Nd(CH CN) ] [(FeCl ) ] •CH CN IX was prepared using a similar procedure, to investigate the
3 9 4 3 3
influence of the anion on the activity. Addition of CH CN to a mixture of NdCl and FeCl in a 1:3
3
3
3
molar ratio, followed by stirring the suspension at room temperature for 24 h, led to a clear purple
solution, from which purple crystals were isolated in 43% yield upon crystallization. The crystals
3+
3–
were characterized to be the expected cationic complex [Nd(CH CN) ] [(FeCl ) ] •CH CN IX
3
9
4 3
3
(Scheme 3). The solid state structure of IX was further determined by an X-ray crystal structural
3+
analysis. As shown in Figure 2, the complex consists of one cation of [Nd(CH CN) ] and three
3
9
–
anions of (FeCl ) . The coordination geometry about the nine-coordinate metal center can be
4
viewed as a distorted tricapped trigonal prism. Each Fe ion in the anion coordinates to four Cl
atoms, forming a distorted tetrahedron. The molecular structure of IX is quite similar to that of the
complex II.
Scheme 3. Synthesis of IX
Figure 2. Molecular structure of IX.
The complex IX was then trialed in the hydroalkoxylation/cyclization of a range of alkenols. The
3
+
3–
results obtained under the same conditions as for the [Nd(CH CN) ] [(AlCl ) ] •CH CN II catalyst
3
9
4 3
3
(Table 3) are listed in Table 6. It can be seen that the complex IX, as an alternative cationic
lanthanide catalyst, also catalyzes the hydroalkoxylation/cyclization of alkenols. However, the
activity is lower than that of II (Table 6, entries 1–4 and Table 3, entries 1, 5, 7, 8), especially for
aromatic alkenols (Table 6, entries 5, 6 and Table 3, entries 11, 12). The comparative study here
1
3

ACCEPTED MANUSCRIPT
revealed the anion in these complexes is also crucial for determining the catalytic activity. It can be
found from the crystallographic data of complexes II and IX that the average Nd−N bond distance
in complex II is longer than that in IX, suggesting that the Ln center in the former is more positive
than that in the latter. It may be the reason for the difference of catalytic activity between II and IX.
a
Table 6. Intramolecular hydroalkoxylation of alkenols catalyzed by IX
Entry
1
Substrate
Product
GC yield (%)
61
1
1
b
f
2
b
2
3
4
92
46
2
f
1
h
2
h
Ph Ph
OH
91
1
i
2
i
OH
b
5
6.7
2
a
1
a
OH
b
6
4.1
2
l
1
l
a
Reactions were catalyzed by 2.5 mol% IX at 83 °C in DCE for 24 h, the substrate
b
concentration is 0.5 mol/L. Solvent CHCl , reaction temperature 65 °C .
3
1
2
.3.3 H NMR spectroscopy study. To gain an insight into which groups (hydroxyl group, C-C
1
double bond or both) coordinate to the Ln metal, an in situ H NMR spectroscopic experiment with
1
b was carried out in CDCl at room temperature in the presence of 1 equiv. VII. As shown in
3
1
Figure 3 (B and C), the signals corresponding to the α–carbon H resonances (∆
δ
= 0.5 ppm) and
5
3+
olefinic H resonances (∆
δ
= 0.06 ppm) were significantly displaced. This indicates that the Ln
1
complexes to both the hydroxyl group and the double bond. As a control, an H NMR experiment
with 1b and 1 equiv. VIII was also conducted under the same conditions (Figure 3A). A similar, but
1
5
smaller, displacement of the H resonances was observed (∆
δ
0.02 ppm for the olefinic H , and ∆
δ
1
1
0
.38 ppm for the α-carbon H ). The smaller variation in the chemical shifts of the H protons,
compared with that for the case of 1b + VII, may be attributed to the weaker interaction of the Al
ion to the alkenol, versus that of the Ln ion to the alkenol. This might be the reason why VIII
3
+
3–
exhibits lower activity than the [Ln(CH CN) ] [(AlCl ) ] •CH CN complex.
3
9
4 3
3
1
4

ACCEPTED MANUSCRIPT
1
Figure 3. H NMR of 1b, 1b + VII, and 1b + VIII.
Unfortunately, attempts to isolate the active species of the catalytic process by mixing 1a and
VI stoichiometrically in CHCl were unsuccessful and no absolute complex was obtained.
3
A reaction pathway was suggested based on the above information, as proposed for the
8b
Ln(OTf) -catalyzed process (Scheme 4). The first step is the coordination of the cationic
3
lanthanide center with both the hydroxyl group and the C=C double bond to yield intermediate A.
Proton transfer then affords intermediate B or B’ with Markovnikov selectivity. Subsequent
alkoxide nucleophilic attack then produces the cyclic ethers and regenerates the catalyst.
3+
3–
Scheme 4. Proposed catalytic pathways for [Ln(CH CN) ] [(AlCl ) ] •CH CN-catalyzed intramolecular
3
9
4 3
3
hydroalkoxylation/cyclization of alkenols
1
5

ACCEPTED MANUSCRIPT
3. Conclusions
We have demonstrated for the first time that cationic lanthanide complexes
3+
3–
[
Ln(CH CN) ] [(AlCl ) ] •CH CN serve as efficient catalysts for the intramolecular
3 9 4 3 3
hydroalkoxylation/cyclization of unactivated aromatic and aliphatic alkenols. The catalytic activity
depends on the Ln metal ion size and solvent used. Various furan, pyran and benzofuran
derivatives were selectively formed as Markovnikov regioselection products in moderate to
excellent yields. A study comparing the activity of three types of cationic complexes,
3
+
3–
2+
2–
[
[
Ln(CH CN) ] [(AlCl ) ] •CH CN,
[AlCl(CH CN) ] [(AlCl ) ] •CH CN,
and
3
9
4 3
3
3
5
4 2
3
3
+
3–
Nd(CH CN) ] [(FeCl ) ] •CH CN, revealed that both the cation and the anion have a great
3
9
4 3
3
influence on the activity of the complex. The much greater activity observed for the cationic Al
complex VIII over the neutral AlCl supports the theory that an increased electron-deficiency of the
3
central metal is the key to activating the hydroxyl and the C=C double bond.
4. Experimental Section
4
.1 General information
All manipulations and reactions were performed under a purified argon atmosphere using
standard Schlenk techniques or under a nitrogen atmosphere in an MBRAUN glovebox. LnCl3
21
were prepared according to the literature procedure. AlCl was sublimed before use. All solvents
3
were predried and distilled before use. Substrates 1a, 1b, 1c, 1d, 1e and 1l were purchased from
Alfa Aesar Co., dried over freshly activated Davison 4Å molecular sieves and were distilled under
4e
4e
4e
4e
5c
5c
6a
6a
6a
6a
reduced pressure. Substrates 1f, 1g, 1h, 1i, 1j, 1k, 1m, 1n, 1o and 1p were
1
13
prepared using reported methods. H and C NMR spectra were recorded on Varian System-300
and INOVA-400 spectrometers. Chemical shifts (δ) were reported in ppm. Gas chromatography
was performed on a Varian CP3800 gas chromatograph equipped with a 30 m HP-5
polydimethylsiloxane capillary column using the following conditions: 80 °C (3
min)//10 °C /min//260 °C (10 min) gradient, detector t emperature 260 °C . Crystals suitable for X-ray
diffraction of complexes (II, VII, VIII and IX) were sealed, respectively, in a thin-walled glass
capillary filled with argon for structural analysis. X-ray diffraction data were collected on a Rigaku
1
6

ACCEPTED MANUSCRIPT
Saturn CCD area detector.
4
.2 Catalyst syntheses
3+
3–
4
.2.1 [Ln(CH CN) ] [(AlCl ) ] •CH CN (Ln = Pr, Nd, Sm, Gd, Er, Yb and Y). This series of cationic
3 9 4 3 3
complexes were synthesized by the reaction between LnCl and AlCl in CH CN according to a
3
3
3
13
reported procedure. Take Sm(CH CN) (AICI ) •CH CN as an example: 0.9 g (6.74 mmol) of
3
9
4 3
3
AICl was added to a slurry of 0.58 g (2.24 mmol) of anhydrous SmCl in 20 mL CH CN and the
3
3
3
reaction mixture was stirred at room temperature for 20 h. The reaction solution was filtrated,
o
concentrated and cooled to 0 C for crystallization, and finally 1.0 g yellow crystals of
Sm(CH CN) (AICI ) •CH CN were collected. The solid state structures of II and VII were
3
9
4 3
3
determined by X-ray crystal structural analysis, as no molecular structures for them had been
reported.
2
+
2–
4
.2.2 [AlCl((CH CN) ] [(AlCl ) ] •CH CN. A suspension of AlCl in CH CN was stirred at room
3 5 4 2 3 3 3
temperature for 24 h. The resulting clear solution was concentrated, and
2+
2–
[
AlCl(CH CN) ] [(AlCl ) ] •CH CN VIII was obtained as colorless crystals by crystallization from a
3 5 4 2 3
mixed solvent of CH CN and hexane at room temperature in almost quantitative yield. The
3
structure of the complex was determined by single-crystal X-ray analysis.
3+
3–
4
.2.3 [Nd(CH CN) ] [(FeCl ) ] •CH CN. A certain amount of CH CN was added to a mixture of
3 9 4 3 3 3
NdCl and FeCl in a 1:3 molar ratio. The suspension was stirred at room temperature for 24 h and
3
3
a clear purple solution was obtained. The solution was concentrated and cooled at 0 °C for several
3+
3–
days to give [Nd(CH CN) ] [(FeCl ) ] •CH CN IX as purple crystals in 43% yield. The structure of
3
9
4 3
3
the complex was determined by single-crystal X-ray analysis.
4
.3 Typical procedure for hydroalkoxylation of unactivated Alkenols (product 2b as an
example)
Into a 10 mL of Schlenk tube under dried argon were added II (0.0265 g, 0.025 mmol), DCE
o
(
2.0 mL) and 4-pentenol (0.10 mL, 1.0 mmol). The resulting mixture was stirred at 83 C for 24 h.
The reaction was cooled to room temperature and the catalyst was removed by filtration through a
short pad of silica gel. Product 2b was obtained by silica-gel column chromatography with
pentane/diethyl ether or petroleum ether/ethyl acetate as an eluent. The GC yield of 90% was
determined with nonane as internal standard.
4
.4. Spectroscopic data
.4.1 2,3-dihydro-2-methylbenzofuran (2a). yellow oil. H NMR (400 MHz, CDCl ): δ =7.27–7.20
8
1
4
3
1
7

(
m, 2 H), 6.97–6.89 (m, 2 H), 5.05
ACCEPTED MANUSC PT
–4.96 (m, 1 H), 3.41–3.3 5R I( dd, J = 15.6, 8.8 Hz, 1 H), 2.93–2.87
13
(dd, J = 15.2, 7.6 Hz, 1 H), 1.58 (d, J = 6.4Hz, 3 H). C NMR (100 MHz, CDCl ): δ = 154.5, 122.9,
3
1
21.9, 119.9, 115.1, 104.2, 74.3, 32.0, 16.7.
8
1
4
.4.2 2-methyltetrahydrofuran (2b). colorless oil. H NMR (400 MHz, CDCl ): δ = 3.88–3.82 (m, 2
3
H), 3.67–3.62 (m, 1 H), 1.93–1.91 (m, 1 H), 1.83–1.81 (m, 2 H), 1.36–1.30 (m, 1 H), 1.16 (d, J =
1
3
6
4
3
.0 Hz, 3 H). C NMR (100 MHz, CDCl ): δ = 75.5, 68.0, 33.5, 26.3, 21.3.
3
8
1
.4.3 2-ethyltetrahydrofuran (2c). colorless oil. H NMR (400 MHz, CDCl ): δ = 3.88–3.82 (m, 1 H),
3
.73–3.70 (m, 2 H), 1.99–1.92 (m, 1 H), 1.87–1.83 (m, 2 H), 1.62–1.56 (m, 1 H), 1.51–1.38 (m, 2
13
H), 0.93 (t, J = 7.6 Hz, 3 H). C NMR (100 MHz, CDCl ): δ = 81.5, 68.4, 31.6, 29.2, 26.4, 11.2.
3
8
1
4
.4.4 2-methyltetrahydropyran (2d). colorless oil. H NMR (300 MHz, CDCl ): δ = 3.89–3.82 (m, 1
3
H), 3.75–3.68 (m, 2 H), 1.88–1.86 (m, 3 H), 1.63–1.56 (m, 1 H), 1.49–1.40 (m, 2 H), 0.91 (d, J = 7.5
13
Hz, 3 H). C NMR (75 MHz, CDCl ): δ = 80.9, 67.8, 31.0, 28.6, 25.8, 10.6.
3
8
1
4
.4.5 2,2,6-trimethyltetrahydropyran (2e). colorless oil. H NMR (400 MHz, CDCl ): δ = 3.70–3.64
3
(m, 1 H), 1.63–1.52 (m, 4 H), 1.41–1.37 (m, 2 H), 1.21 (s, 3 H), 1.19 (s, 3 H), 1.10 (d, J = 8.0 Hz, 3
13
H). C NMR (100 MHz, CDCl ): δ = 67.1, 61.8, 31.4, 28.8, 27.4, 18.2, 17.4, 15.5.
3
8
1
4
.4.6 2-methyl-4,4-diphenyltetrahydrofuran (2f). off-white solid. H NMR (400 MHz, CDCl ): δ =
3
7
.31–7.20 (m, 10 H), 4.60–4.58 (m, 1 H), 4.19–4.16 (m, 2 H), 2.66–2.61 (m, 1 H), 2.30–2.24 (m, 1
13
H), 1.29 (d, J = 6.4 Hz, 3 H). C NMR (100 MHz, CDCl ): δ = 146.9, 146.8, 128.9, 128.8, 127.7,
3
1
4
7
26.9, 126.7, 75.3, 55.9, 47.1, 30.2, 21.9.
8
1
.4.7 2-methyl-5,5-diphenyltetrahydropyran (2g). colorless oil. H NMR (400 MHz, CDCl ): δ =
3
.45–7.18 (m, 10 H), 4.66–4.63 (m, 1 H,), 3.59–3.16 (m, 2 H), 2.46–2.43 (m, 2 H), 1.58–1.54 (m, 1
13
H), 1.27–1.23 (m, 1 H), 1.19–1.18 (m, 3 H). C NMR (100 MHz, CDCl ): δ = 147.3, 146.4, 129.5,
3
1
28.8, 128.5, 127.5, 126.8, 126.2, 75.6, 74.6, 46.3, 35.3, 30.3, 22.2.
5c
1
4
.4.8 2,2-dimethyl-5,5-diphenyltetrahydropyran (2h). off-white solid. H NMR (400 MHz, CDCl ):
3
δ = 7.29–7.22 (m, 8 H), 7.16–7.12 (m, 2 H), 4.02 (s, 2 H), 2.41–2.38 (m, 2 H), 1.38–1.35 (m, 2 H),
1
3
1
3
4
7
.19 (s, 6 H). C NMR (100 MHz, CDCl ): δ = 146.6, 128.2, 128.1, 126.1, 71.4, 69.1, 46.0, 32.7,
3
0.9, 26.5.
4e
1
.4.9 2,2-dimethyl-5,5-diphenyltetrahydrofuran (2i). white solid. H NMR (400 MHz, CDCl ): δ =
3
13
.27–7.24 (m, 8 H), 7.18–7.14 (m, 2 H), 4.43 (s, 2 H), 2.60 (s, 2 H), 1.18 (s, 6 H). C NMR (100
MHz, CDCl ): δ = 147.0, 128.5, 127.4, 126.3, 81.6, 75.6, 56.9, 51.6, 29.4.
3
5c
1
4
.4.10 2,2-dimethyl-4-Naphthyltetrahydrofuran (2j). light yellow solid. H NMR (300 MHz, CDCl ):
3
δ = 8.14 (d, J = 6.0 Hz, 1 H), 7.89–7. 73 (m, 2 H), 7.55–7.44 (m, 4 H), 4.42–4.26 (m, 2 H),
13
4
.02–3.97 (m, 1 H), 2.36 (t, J = 28.0 Hz, 1 H), 2.09 (t, J = 28.0 Hz, 1 H), 1.42 (s, 6 H). C NMR
(
100 MHz, CDCl ): δ = 137.9, 134.0, 132.2, 129.0, 127.2, 126.1, 125.6, 123.5, 122.9, 81.2, 72.6,
3
4
6.0, 41.3, 29.0, 28.5.
1
8

5
c
1
4
8
2
0
1
4
6
ACCEPTED MANUS T
3
.4.11 3-naphthyloctahydrobenzofuran (2k). light yello wC Rs oI Pl id. H NMR (300 MHz, CDCl ): δ =
.13 (d, J = 6 Hz, 1 H), 7.87–7.73 (m, 2 H), 7.52–7.38 (m, 4 H), 4.62–4.57 (m, 1 H), 4.40–4.36 (m,
H), 4.26–4.21 (m, 1 H), 2.46 (s, 1 H), 2.11–2.07 (m, 1 H), 1.59–1.46 (m, 5 H), 1.12–0.97 (m, 2 H),
13
.66–0.62 (m, 1 H). C NMR (100 MHz, CDCl ): δ = 133.9, 133.5, 132.6, 129.0, 127.2, 126.0,
3
25.6, 125.0, 123.7, 123.2, 78.8, 68.3, 45.2, 41.6, 28.9, 4.3.6, 23.2, 20.5.
6a
1
.4.12 2,7-dimethyl-2,3-dihydrobenzofuran (2l). yellow oil. H NMR (400 MHz, CDCl ): δ =
3
.99–6.91 (m, 2 H), 6.75–6.71 (m, 1 H), 4.94–4.86 (m, 1 H), 3.33–3.27 (m, 1 H), 2.84–2.78 (m, 1
13
H), 2.20 (s, 3 H), 1.48 (d, J = 8 Hz, 3 H). C NMR (100 MHz, CDCl ): δ = 158.5, 129.6, 126.7,
3
1
4
6
1
22.8, 120.5, 119.9, 79.6, 37.9, 22.4, 15.8.
6a
1
.4.13 2,5-dimethyl-2,3-dihydrobenzofuran (2m). colorless oil. H NMR (400 MHz, CDCl ) δ =
3
.96 (s, 1 H), 6.89 (d, J = 8.1 Hz, 1 H), 6.64 (d, J = 8.0 Hz, 1 H), 4.98–4.74 (m, 1 H), 3.26 (dd, J =
13
5.4, 8.7 Hz, 1 H), 2.77 (dd, J = 15.4, 7.7 Hz, 1 H), 2.27 (s, 3 H), 1.45 (d, J = 6.2 Hz, 3 H). C NMR
(
100 MHz, CDCl ): δ = 157.5, 129.5, 128.3, 127.2, 125.7, 108.9, 79.6, 37.3, 21.8, 20.9.
3
6a
1
4
.4.14 5-methoxy-2-methyl-2,3-dihydrobenzofuran (2n). colorless oil. H NMR (400 MHz, CDCl )
3
δ = 6.74 (s, 1 H), 6.69–6.60 (m, 1 H), 4.96–4.78 (m, 1 H), 3.74 (s, 3 H), 3.27 (dd, J = 15.5, 8.6 Hz,
1
3
1
1
4
=
=
H), 2.79 (dd, J = 15.5, 7.8 Hz, 1 H), 1.45 (d, J = 6.2 Hz, 3 H). C NMR (100 MHz, CDCl ): δ =
3
54.0, 153.7, 128.1, 112.7, 111.4, 109.1, 79.7, 56.0, 37.7, 21.8.
6a
1
.4.15 5-chloro-2-methyl-2,3-dihydrobenzofuran (2o). colorless oil. H NMR (400 MHz, CDCl ) δ
3
7.08 (s, 1 H), 7.03 (d, J = 8.5 Hz, 1 H), 6.65 (d, J = 8.4 Hz, 1 H), 5.06 –4.76 (m, 1 H), 3.27 (dd, J
13
15.6, 8.8 Hz, 1 H), 2.78 (dd, J = 15.6, 7.6 Hz, 1 H), 1.44 (d, J = 6.3 Hz, 3 H). C NMR (100 MHz,
CDCl ): δ = 158.3, 129.1, 127.9, 125.2, 116.1, 110.3, 80.3, 37.1, 21.8.
3
6
a
1
4
=
3
.4.16 5-bromo-2-methyl-2,3-dihydrobenzofuran (2p). colorless oil. H NMR (400 MHz, CDCl ) δ
3
7.21 (d, J = 8.5 Hz, 1 H), 7.17 (d, J = 8.5 Hz, 1 H), 6.61 (d, J = 8.4 Hz, 1 H), 5.01–4.80 (m, 1 H),
1
3
.27 (dd, J = 15.6, 8.8 Hz, 1 H), 2.78 (dd, J = 15.6, 7.6 Hz, 1 H), 1.44 (d, J = 6.2 Hz, 3 H). C NMR
(
100 MHz, CDCl ): δ = 158.7, 130.7, 129.6, 127.9, 111.8, 110.8, 80.1, 36.9, 21.7.
3
Acknowledgements
We are grateful to the National Natural Science Foundation of China (Grant Nos. 21272168
and 21372171) and Specialized Research Fund for the Doctoral Program of Higher Education
(200802850003).
Supplementary data
1
Supplementary data (crystallographic data for complexes II, VII, VIII, and IX and copies of H
13
NMR and C NMR spectra of compounds 2a-2p) related to this article can be found.
1
9

ACCEPTED MANUSCRIPT
Reference
(
1) (a) Elliott, M. C.; Williams, E. J. Chem. Soc. Perkin Trans. 1 2001, 2303–2340. (b) Yao, Z.-Y.;
Wu, H.-P.; Wu, Y.-L. J. Med. Chem. 2000, 43, 2484–2487. (c) Mitchenson, A.; Nadin, A. J.
Chem. Soc. Perkin Trans. 1 2000, 2862–2892. (d) Elliott, M. C. J. Chem. Soc. Perkin Trans. 1
2
000, 1291–1318. (e) Boivin, T. L. B. Tetrahedron 1987, 43, 3309–3362.
(
2) Larock, R. C.; Leong, W. W. Comprehensive Organic Synthesis; Trost, B. M., Fleming, I., Eds.;
Pergamon Press: New York, 1991; Vol. 4.
(
3) For examples of Brønsted acid mediated alkene hydroalkoxylation, see: (a) Rosenfeld, D. C.;
Shekhar, S.; Tameiyama, A.; Utsunomiya, M.; Hartwig, J. F. Org. Lett. 2006, 8, 4179–4182. (b)
Coulombel, L.; Duñach, E. Green Chem. 2004, 6, 499–501. (c) Wang, B.; Gu, Y.; Yang, L.; Suo,
J.; Kenichi, O. Catal. Lett. 2004, 96, 71–74. (d) Linares-Palomino, P. J.; Salido, S.; Altarejos, J.;
Snchez, A. Tetrahedron Lett. 2003, 44, 6651–6655.
(
4) For examples of transition-metal-mediated alkene hydroalkoxylation, see: (a) Yang, C.-G.; He
C. J. Am. Chem. Soc. 2005, 127, 6966–6967. (b) Coulombel, L.; Favier, I.; Duñach, E. Chem.
Commun. 2005, 2286–2288. (c) Oe, Y.; Ohta, T.; Ito, Y. Synlett 2005, 179–181. (d) Oe, Y.;
Ohta, T.; Ito, Y. Chem. Commun. 2004, 1620–1621. (e) Qian, H.; Han, X.; Widenhoefer, R. A. J.
Am. Chem. Soc. 2004, 126, 9536–9537. (f) Marotta, E.; Foresti, E.; Marcelli, T.; Peri, F.; Righi,
P.; Scardovi, N.; Rosini, G. Org. Lett. 2002, 4, 4451–4453. (g) Hori, K.; Kitagawa, H.; Miyoshi,
A.; Ohta, T.; Furukawa, T. I. Chem. Lett. 1998, 1083–1084.
(
5) For examples of metal-triflate-mediated alkene hydroalkoxylation, see: (a) Komeyama, K.;
Morimoto, T.; Nakayama, Y.; Takaki, K. Tetrahedron Lett. 2007, 48, 3259–3261. (b) Coulombel,
L.; Rajzmann, M.; Pons, J. M.; Olivero, S.; Duñach, E. Chem. Eur. J. 2006, 12, 6356–6365. (c)
Yang, C.-G.; Reich, N. W.; He, C. Org. Lett. 2005, 7, 4553–4556. (d) Coulombel, L.; Favier, I.;
Dunach, E. Chem. Commun. 2005, 2286–2288. (e) Brendan, D. K.; Julia, M. A.; Rachel, E. T.;
Tristan, H. L. Org. Lett. 2009, 11, 1381–1383.
(
6) (a) Schlüter, J.; Blazejak, M.; Hintermann, L. ChemCatChem 2013, 5, 3309–3315. (b) Diba, A.;
Begouin, J.; Niggemann, M. Tetrahedron Lett. 2012, 53, 6629–6632. (c) Kong, L.; Lin, Q.; Lv,
X.; Yang, Y.; Jia, Y.; Zhou, Y. Green Chem. 2009, 11, 1108–1111. (d) Grant, V. H.; Liu, B.
Tetrahedron Lett. 2005, 46, 1237–1239.
(7) (a) Seo, S.; Yu, X.; Marks, T. J. J. Am. Chem. Soc. 2009, 131, 263–276. (b) Yu, X.; Seo, S.;
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Marks, T. J. J. Am. Chem. Soc. 2007, 129, 7244–7245. (c) Seo, S.; Marks, T. J. Chem. Eur. J.
2
010, 16, 5148–5162.
(
8) (a) Dzudza, A.; Marks, T. J. Org. Lett. 2009, 11, 1523-1526. (b) Dzudza, A.; Marks, T. J. Chem.
Eur. J. 2010, 16, 3403–3422.
(
9) (a) Zeimentz, P. M.; Arndt, S.; Elvidge, B. R. J. Okuda, Chem. Rev. 2006, 106, 2404–2433. (b)
Luo, Y. Feng, X.; Wang, Y.; Fan, S.; Chen, J.; Lei, Y.; Liang, H. Organometallics 2011, 30,
3
270–3274. (c) Tardif, O.; Kaita, S. Dalton Trans. 2008, 2531–2533. (d) Xu, X.; Chen, Y.; Sun,
J. Chem. Eur. J. 2009, 15, 846–850. (e) Visseaux, M.; Mainil, M.; Terrier, M.; Mortreux, A.;
Roussel, P.; Mathivet, T.; Destarac, M. Dalton Trans. 2008, 4558–4561. (f) Binda, P. I.;
Delbridge, E. E. Dalton Trans. 2007, 4685–4692. (g) Sheng, H.; Zhou, H.; Guo, H.; Sun, H.;
Yao, Y.; Wang, J.; Zhang, Y.; Shen, Q. J. Organomet. Chem. 2007, 692, 1118–1124.
(10) Lauterwasser, F.; Hayes, P. G.; Bra¨se, S.; Piers, W. E.; Schafer, L. L. Organometallics 2004,
2
3, 2234–2237.
(
11) Tazelaar, C. G. J.; Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J. H.
Organometallics 2004, 23, 936–939.
(
(
(
(
12) Molander, G. A.; Rzasa, R. M. J. Org. Chem. 2000, 65, 1215–1217.
13) Hu, J.; Shen, Q.; Jin, Z. Chin. Sci. Bull. 1989, 34, 1554–1556.
14) Hu, J.; Shen, Q. Chinese J. Catal. 1990, 11, 16–20.
15) CCDC 1442486 (II) and CCDC 1442482 (VII) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
(
(
(
(
16) (a) Hong, S.; Marks, T. J. Acc. Chem. Res. 2004, 37, 673–686. (b) Arredondo, V. M.;
McDonald, F. E.; Marks, T. J. Organometallics 1999, 18, 1949–1960.
17) (a) Ryu, J.-S.; Marks, T. J.; McDonald, F. E. J. Org. Chem. 2004, 69, 1038–1052. (b) Ryu,
J.-S.; Marks, T. J.; McDonald, F. E. Org. Lett. 2001, 3, 3091–3094.
18) (a) Seo, S.; Yu, X.; Marks, T. J. J. Am. Chem. Soc. 2009, 131, 263–276. (b) Yu, X.; Seo, S.;
Marks, T. J. J. Am. Chem. Soc. 2007, 129, 7244–7245.
19) CCDC 1442485 (VIII) contains the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
(
20) CCDC 1442484 (IX) contain the supplementary crystallographic data for this paper. These
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data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
(21) Taylor, M. D.; Carter, C. P. J. Inorg. Nucl. Chem. 1962, 24, 387–391.
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