Ruthenium(III)-Catalyzed β-Alkylation of Secondary Alcohols with Primary Alcohols

Article abstract of DOI:10.1021/acs.organomet.6b00130

A Ru(III)-NNN complex bearing a pyridyl-supported pyrazolyl-imidazolyl ligand was synthesized and utilized as the catalyst for the direct β-alkylation of secondary alcohols with primary alcohols. β-Alkylated secondary alcohols were obtained in moderate to high yields with water formed as the byproduct through a hydrogen borrowing pathway. The present protocol provides a concise atom-economical and environmentally benign method for C-C bond formation.

Full text of DOI:10.1021/acs.organomet.6b00130

Article
pubs.acs.org/Organometallics
Ruthenium(III)-Catalyzed β‑Alkylation of Secondary Alcohols with
Primary Alcohols
Qingfu Wang, Kaikai Wu, and Zhengkun Yu*
†
†
,†,‡
†
Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian, Liaoning 116023, China
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354
‡
Fenglin Road, Shanghai 200032, China
*
S Supporting Information
ABSTRACT: A Ru(III)-NNN complex bearing a pyridyl-supported pyrazolyl-
imidazolyl ligand was synthesized and utilized as the catalyst for the direct β-
alkylation of secondary alcohols with primary alcohols. β-Alkylated secondary
alcohols were obtained in moderate to high yields with water formed as the
byproduct through a hydrogen borrowing pathway. The present protocol
provides a concise atom-economical and environmentally benign method for C−
C bond formation.
1
1
INTRODUCTION
type oxidation of secondary alchohols (Scheme 1). Ru(II)
■
complexes A−C and their analogues have exhibited very high
Alcohols are one of the most important intermediates that have
been widely used in organic synthesis and chemical industry.
Traditional routes to access β-alkylated alcohols from
secondary alcohols usually require a multistep process that
involves oxidation of secondary alcohols, alkylation with alkyl
halides, and reduction of β-alkylated ketones. Considering the
demand of environmentally benign processes, transition-metal-
catalyzed direct β-alkylation of secondary alcohols with primary
alcohols has been widely studied as a greener route through a
hydrogen borrowing or hydrogen autotransfer strategy in
Scheme 1. Selected NNN Ligands and Their Corresponding
Ruthenium Complexes
1
recent years. This alternative method involves a dehydrogen-
ation of alcohol to ketone or aldehyde, followed by aldol
reaction, generating the corresponding enone intermediate, and
subsequent hydrogenation of the enone to afford β-alkylated
alcohols with high atom efficiency by producing water as the
only byproduct. Cho et al. reported such a direct β-alkylation
with RuCl (PPh ) as the catalyst, but sacrificial hydrogen
2
3 3
2
acceptor and hydrogen donor were needed. RuCl (DMSO)
was found to be a more efficient catalyst for the same purpose.
2
4
3
Ruthenium complexes containing a chelating N-heterocyclic
carbene and other types of ligands were efficiently used fo4r
direct β-alkylation of secondary alcohols with primary alcohols.
Highly active iridium complexes, such as [Cp*IrCl ] and
2
2
5
iridium-NHC complexes, have also been applied in this area.
catalytic activities in these transformations. Unexpectedly,
Tris(acetylacetonato)rhodium(III) was shown to be a suitable
catalyst for the alkylation of secondary alcohols in the presence
Ru(III) complex D also acted as an efficient catalyst for the
11l
6
transfer hydrogenation of ketones. As compared to the
of 1,4-diazabicyclo[2.2.2]octane (DABCO). β-Alkylation of
12
7
extensively investigated Ru(II) complexes, Ru(III) complexes
13
secondary alcohols can also be realized by using palladium,
8
9
have been paid much less attention. In the latter case, Ru(III)
14
copper, and iron complex catalysts or under metal-free
1
0
complexes were reported as the catalysts for C−H activation,
conditions.
15
heterocycle synthesis, and transfer hydrogenation of
Recently, we have reported a series of versatile symmetrical
and unsymmetrical pyridyl-based N-heterocylic ligands and the
application of their corresponding ruthenium complexes as the
catalysts for transfer hydrogenation of ketones and Oppenauer-
Received: February 15, 2016
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.6b00130
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Organometallics
Article
1
6
ketones. During our ongoing exploration of ruthenium-
catalyzed transfer hydrogenation of ketones, we reasonably
envisioned that the ruthenium(III) complex of ligand L2, that
is, complex 1, might be used as the catalyst for β-alkylation of
secondary alcohols with primary alcohols. Herein, we report
ruthenium(III)-NNN complex-catalyzed β-alkylation of secon-
dary alcohols with primary alcohols through a hydrogen
borrowing pathway.
yield, with formation of ketone 5a as the minor product (Table
1, entry 1). The conversions and selectivities were obviously
improved by addition of a pyridyl-based NNN ligand, that is,
one of L1−L4 (Table 1, entries 2−5). Encouraged by L2 as a
promising ligand to stabilize the Ru(III) catalyst (Table 1, entry
3), complex 1 was synthesized and tested as the catalyst for the
same reaction. To our delight, complex 1 (1.0 mol %)
promoted the reaction to reach 95% conversion for 2a and 90%
selectivity for 4a (Table 1, entry 6). Under the solvent-free
conditions, the conversion and selectivity were further
improved (Table 1, entry 7). Among the screened bases,
KOH acted as the most suitable base for the desired reaction
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Ru(III) Complex 1.
Reacting equimolar amounts of ligand L2 with RuCl ·xH O in
refluxing ethanol gave Ru(III) complex 1 in 85% yield (eq 1).
Ru(III) complex 1 is paramagnetic, and its NMR spectra could
not be successfully collected. Complex 1 was characterized by
HRMS, elemental analysis, and IR. The HRMS analysis of
complex 1 revealed a peak corresponding to value of 460.9750
[M − Cl] ), which is consistent with the calculated value of
60.9748 for the composition of the RuCl ·L2 adduct.
3
2
(
2
Table 1, entries 7−10). A catalytic amount of the base, that is,
0 mol % KOH, also effected the reaction to reach the best
reaction efficiency: >99% conversion for 2a with a 93:7 molar
ratio of 4a:5a. Thus, 4a was isolated in 90% yield (Table 1,
entry 11). Both the Ru(II) complexes RuCl (PPh ) and
2
3 3
+
[RuCl (p-cymene)] demonstrated poor catalytic activity for
(
4
2 2
the reaction (Table 1, entries 12 and 13). Under atmospheric
oxygen, the reaction efficiency was obviously deteriorated
3
Compared with the ligand L2 infrared spectrum, the CN
(
Table 1, entry 14).
Under the optimized conditions, the protocol generality was
stretching vibration of complex 1 moved from 1580 to 1609
−1
cm due to the coordination effect of the ligand with the
explored by using a variety of primary alcohols (Table 2).
Benzylic alcohols bearing an electron-donating methyl,
methoxy, or 3,4-methylenedioxy substituent reacted with 2a
to form the desired products 4b−4f in 81−91% yields.
Electron-deficient substituent-bearing benzylic alcohols, that
is, 2-, 3-, or 4-chlorobenzyl alcohols, also smoothly reacted with
ruthenium metal center.
2a to afford products 4g−4i in good yields (78−91%).
However, the reactions of the alcohol substrates bearing an
ester, amide, aldehyde, or cyanide substituent on the aryl
moiety gave no identified products. Such substituents under-
went decomposition to mess the reactions under the reaction
conditions. In the case of benzylic alcohol bearing a benzoyl
substituent, its reaction with 1-phenylethanol formed the
intermediate ketone product 5j in 52% yield. The reaction of
β-Alkylation of Secondary Alcohols with Primary
Alcohols. Initially, the reaction of 1-phenylethanol (2a) with
benzyl alcohol (3a) was conducted to optimize the reaction
conditions (Table 1). By using 1 mol % RuCl ·xH O as the
3
2
catalyst and 100 mol % KOH as the base in toluene at 110 °C,
the corresponding β-alkylated product 4a was obtained in 30%
2
a with 2-naphthylmethanol efficiently underwent, forming 4k
a
Table 1. Screening of the Reaction Conditions
in 88% yield. Use of 2-pyridylmethanol decreased the yield of 4l
to 64%, whereas the corresponding 4-pyridylmethanol reacted
with 2a to give the desired product 4m in 75% yield, which
reveals an electronic effect from the pyridyl moiety.
Unexpectedly, 2-furylmethanol reacted to give 4n in a good
yield (76%). Somehow, use of chain-varying aliphatic primary
alcohols only led to the desired products 4o−4s in 52−70%
yields by increasing the catalyst loading to 2.0 mol % and
extending the reaction time to 12 h.
Next, the scope of the secondary alcohols (2) was
investigated (Table 3). The present catalytic system could be
tolerant with various functional groups. Steric hindrance from
the aryl moieties of 2 had no obvious impact on the reaction
efficiency. Thus, 1-(2-methylphenyl)ethanol reacted with 3a to
afford the desired product 6a in 93% yield. Secondary alcohols
bearing a meta-Me, or -OMe or para-OMe group also
underwent the reaction efficiently to form 6b−6d in 87−90%
yields. Electron-withdrawing substituents such as bromo and
chloro lessened the reaction efficiency to some extent, leading
to the desired products 6e−6g in 74−82% yields. In the same
fashion, treatment of 1-(2-naphthyl)ethanol with 3a resulted in
6h in 91% yield. 1-(2-Pyridyl)ethanol reacted with 3a to give 6i
in a good yield (80%). However, the long-chain secondary
alcohols only exhibited relatively low reactivity to 3a, and their
reactions had to be performed to form 6j−6l in 53−76% yields
in the presence of 2.0 mol % catalyst over a period of 12 h.
conversion of
4a:5a
b
b
entry
catalyst
base
2a (%)
(molar ratio)
1
RuCl ·xH O
RuCl ·xH O/L1
3 2
KOH
KOH
KOH
KOH
KOH
KOH
KOH
tBuOK
NaOH
K PO
30
60
67:33
75:25
86:14
72:28
65:35
90:10
93:7
3
2
2
3
4
5
6
7
8
9
1
1
1
1
1
RuCl ·xH O/L2
89
3
2
RuCl ·xH O/L3
49
3
2
RuCl ·xH O/L4
52
3
2
1
1
1
1
1
1
95
c
c
c
>99
81
91:9
75
77:23
n.d.
c
c
c
c
c
0
1
2
3
4
<5
>99
15
3
4
,
,
,
,
d
d
d
d
e
KOH
93:7 (90)
RuCl (PPh )
3 3
KOH
KOH
KOH
55:45
n.d.
2
[RuCl (p-cymene)]
<5
80
2
2
,
f
1
80:20
a
Conditions: 2a (2.0 mmol), 3a (2.0 mmol), catalyst (1.0 mol %),
base (2.0 mmol), toluene (1 mL), 0.1 MPa N , 110 °C, 6 h. The
reaction was performed in a 25 mL sealed tube. Determined by GC
2
b
c
d
e
analysis. Solvent-free. Using 0.2 equiv of KOH. Isolated yield of 4a
f
given in parentheses. Under 0.1 MPa O atmosphere.
2
B
DOI: 10.1021/acs.organomet.6b00130
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Article
Table 2. Scope of Primary Alcohols (3)a,b
a
b
c
Conditions: 2a (2.0 mmol), 3 (2.0 mmol), 1.0 mol % 1, 20 mol % KOH, 0.1 MPa N , 110 °C, 6 h. Isolated yields. 2.0 mol % 1, 12 h.
2
Table 3. Generality of Secondary Alcohols (2) ,
ab
a
b
c
Conditions: 2 (2.0 mmol), 3a (2.0 mmol), 1.0 mol % 1, 20 mol % KOH, 0.1 MPa N , 110 °C, 6 h. Isolated yields. 2.0 mol % 1, 12 h.
2
C
DOI: 10.1021/acs.organomet.6b00130
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Organometallics
Article
Scheme 2. Reactions of Cyclopentanol with Benzylic Alcohols
Then, cyclic secondary alcohols, that is, cyclopentanol 7, was
employed to react with various primary alcohols in the same
fashion (Scheme 2). Interestingly, 7 reacted with benzyl
alcohols to afford dialkylated secondary alcohol products of
type 8. The reaction of cyclopentanol with benzylic alcohol
formed 2,5-dibenzylcyclopentanol 8a (74%). The electron-
donating 4-methoxy and 3,4-methylenedioxy substituents
varied the product yields of 8b (75%) and 8c (85%). The
electronic and steric effects are obvious for the electron-
withdrawing chloro and fluoro substituents on the aryl moiety
of the benzylic alcohols, rendering formation of 8d−8g in 52−
potential strategy that combines simple metal salts with
polydentate ligands to explore the catalytic activity of the
possible catalyst systems.
EXPERIMENTAL SECTION
General Considerations. The solvents were dried and distilled
prior to use by the literature methods. H and C{ H} NMR spectra
■
1
13
1
were recorded on a Bruker DRX−400 spectrometer, and all chemical
1
shift values refer to δ
= 0.00 ppm, CDCl (δ( H), 7.26 ppm;
TMS
3
13
δ( C), 77.16 ppm). The HRMS analysis was obtained on an Agilent
6
540 UHD Q-TOF mass spectrometer. All the melting points were
uncorrected. TLC analysis was performed by using glass-backed plates
coated with 0.2 mm of silica gel. Flash column chromatography was
performed on silica gel. All the chemical reagents were purchased from
commercial sources and used as received unless otherwise indicated.
Ligands L1, L2, L3, and L4 were prepared as reported.
Synthesis of Complex 1. Under a nitrogen atmosphere, a mixture of
RuCl ·xH O (262 mg, 1.0 mmol) and ligand L2 (289 mg, 1.0 mmol)
82% yields.
Reaction Mechanism. A simplified mechanism is proposed
in Scheme 3. Initially, the precatalyst Ru(III) complex 1 was
1
1b
11c
11i
11l
Scheme 3. Proposed Mechanism
3
2
in ethanol (20 mL) was refluxed for 3 h. After it cooled to ambient
temperature, the mixture was filtered and the residue was rinsed with
diethyl ether (3 × 10 mL), and dried in vacuo to afford 1 as a brown
powder (421 mg, 85% yield). Mp: > 300 °C dec. IR (KBr pellets,
−
1
cm ): ν 3528, 3136, 1609, 1559, 1470, 1405, 1356, 1322, 1235, 1160,
1
095, 1058, 984, 798, 764, 434. Anal. Calcd for C H Cl N Ru: C,
17 15 3 5
4
1.10; H, 3.04; N, 14.10. Found: C, 40.64; H, 2.89; N, 14.11. HRMS:
+
calcd for C H Cl N Ru, [M − Cl] 460.9748, found 460.9750.
17
15
3
5
General Procedure for Ru(III)-Catalyzed β-Alkylation of Secon-
dary Alcohols with Primary Alcohols: Synthesis of 1,3-Diphenyl-
propan-1-ol (4a). Under a nitrogen atmosphere, a mixture of complex
1
(10 mg, 0.02 mmol), KOH (22 mg, 0.4 mmol), 1-phenylethanol
(
2a) (244 mg, 2.0 mmol), and benzyl alcohol (3a) (216 mg, 2.0
transformed to a pentacoordinated complex by extrusion of one
molecule of HCl in the presence of KOH and then reduced to
mmol) was loaded in a 25 mL sealed tube and stirred at 110 °C for 6
h. After it cooled to ambient temperature, the mixture was filtered
11l
Ru(II) species under the reaction conditions. The Ru(II)
species generated in situ promotes oxidation of the secondary
and primary alcohols to the corresponding ketone and aldehyde
through a short pad of Celite and rinsed with 20 mL of CH Cl . The
2 2
combined filtrate was concentrated under reduced pressure, and the
resulting residue was purified by column chromatography on silica gel
(eluent petroleum ether (60−90 °C)/ethyl acetate: 20:1, v/v) to
afford 4a as a white solid (382 mg, 90%).
1g
by generation of a ruthenium hydride species. Then, the base
mediated cross-aldol condensation of the in situ formed ketone
and aldehyde to form the α,β-unsaturated ketone intermediate.
Subsequent transfer hydrogenation of the resultant enone with
the ruthenium hydride species yields the coupled alcohol. The
possible catalytically RuH species was not successfully prepared
General Procedure for Ru(III)-Catalyzed β-Alkylation of Cyclo-
pentanol with Primary Alcohols: Synthesis of 2,5-Dibenzylcyclo-
pentanol (8a). Under a nitrogen atmosphere, a mixture of complex 1
(10 mg, 0.02 mmol), KOH (11 mg, 0.2 mmol), cyclopentanol (7) (86
mg, 1.0 mmol), and benzyl alcohol (3a) (216 mg, 2.0 mmol) was
loaded in a 25 mL sealed tube and stirred at 130 °C for 12 h. After it
cooled to ambient temperature, the mixture was filtered through a
short pad of Celite and rinsed with 20 mL of CH Cl . The combined
11j
from complex 1 under the reported basic conditions.
2
2
CONCLUSIONS
■
filtrate was concentrated under reduced pressure, and the resulting
residue was purified by column chromatography on silica gel (eluent
petroleum ether (60−90 °C)/ethyl acetate: 20:1, v/v) to afford 8a as a
white solid (197 mg, 74%).
In summary, we have developed an efficient Ru(III)-NNN
complex-catalyzed direct β-alkylation of secondary alcohols
with primary alcohols. The present protocol provides a
D
DOI: 10.1021/acs.organomet.6b00130
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Synthesis of 2,5-Bis(4-methoxybenzyl)cyclopentanol (8b). In a
fashion similar to the synthesis of 8a, cyclopentanol (7) (86 mg, 1.0
mmol) reacted with 4-methoxybenzyl alcohol (3b) (276 mg, 2.0
(aromatic CH), 83.2 (CHOH), 47.7, 32.7 (d, J = 1.7 Hz) and 27.0.
HRMS: calcd for C H F O 302.1482, found 302.1471.
19
20 2
mmol) to afford 8b as a white solid (244 mg, 75% yield). Mp: 65−66
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00130.
■
1
°
C. H NMR (CDCl , 400 MHz): δ 7.13 and 6.85 (d each, J = 8.5 Hz,
3
*
S
4
:4 H, aromatic CH), 3.79 (s, 6 H, 2 × OCH ), 3.42 (t, J = 8.2 Hz, 1
3
H, CHOH), 2.84 and 2.52 (q each, 2:2 H, 2 × CH ), 2.01 (m, 2 H, 2
2
×
CH), 1.73 and 1.28 (m each, 2:2 H, 2 × CH ), 1.41 (br, 1 H, OH).
2
1
3
1
C{ H} NMR (CDCl , 100 MHz): δ 158.0 and 133.2 (Cq each),
3
1
3
29.8 and 113.9 (aromatic CH), 83.2 (CHOH), 55.3 (OCH ), 48.9,
NMR spectra of all compounds (PDF)
3
9.2, and 27.2. HRMS: calcd for C H O 326.1882, found 326.1877.
21
26
3
Synthesis of 2,5-Bis(benzo[d][1,3]dioxol-5-ylmethyl)cyclo-
pentanol (8c). In a fashion similar to the synthesis of 8a,
cyclopentanol (7) (86 mg, 1.0 mmol) reacted with 3,4-(methylene-
AUTHOR INFORMATION
Corresponding Author
*E-mail: zkyu@dicp.ac.cn (Z.Y.).
Notes
■
dioxy)benzyl alcohol (3c) (304 mg, 2.0 mmol) to afford 8c as a white
1
solid (301 mg, 85% yield). Mp: 124−125 °C. H NMR (CDCl , 400
3
MHz): δ 6.74 (m, 6 H, aromatic CH), 5.93 (d, J = 3.5 Hz, 4 H, 2 ×
The authors declare no competing financial interest.
OCH O), 3.84 (m, 1 H, CHOH), 2.82, 2.65, 2.57, and 2.48 (q each,
2
1
:1:1:1 H, 2 × CH ), 2.15 (m, 2 H, 2 × CH), 1.92, 1.70, 1.50, and 1.24
2
13 1
ACKNOWLEDGMENTS
We are grateful to the National Natural Science Foundation of
China (21272232).
(
m each, 1:2:1:1 H, 2 × CH and OH). C{ H} NMR (CDCl , 100
■
2
3
MHz): δ 147.61, 147.59, 145.7, 145.6, 135.6, and 134.9 (Cq each),
21.6, 121.4, 109.20, 109.19, 108.14, and 108.12 (aromatic CH), 100.8
1
and 100.7 (2 × OCH O), 78.5 (CHOH), 49.7, 45.6, 40.4, 35.0, 29.0,
2
and 28.8. HRMS: calcd for C H O 354.1467, found 354.1466.
21
22
5
REFERENCES
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■
Synthesis of 2,5-Bis(4-chlorobenzyl)cyclopentanol (8d). In a
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mmol) reacted with 4-chlorobenzyl alcohol (3d) (285 mg, 2.0 mmol)
(
́
, D. J.;
Yus, M. Angew. Chem., Int. Ed. 2007, 46, 2358−2364. (b) Nixon, T. D.;
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(
(
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1
H NMR (CDCl , 400 MHz): δ 7.16 (m, 4 H, aromatic CH), 7.66 and
3
7
2
2
.01 (d each, J = 8.4 Hz, 2:2 H, aromatic CH), 3.71 (m, 1 H, CHOH),
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2
2
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2
1
(
br, 1 H, OH). 13C{ H} NMR (CDCl , 100 MHz): δ 140.3, 139.5,
3
(
1
31.9, and 131.6 (Cq each), 130.24, 130.22, 128.62, and 128.58
aromatic CH), 78.6 (CHOH), 49.7, 45.5, 40.1, 34.8, 29.1, and 29.0.
HRMS: calcd for C H Cl O 334.0891, found 334.0887.
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(
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19
20
2
1
(
8
(
4, 10201−10205.
Synthesis of 2,5-Bis(3-chlorobenzyl)cyclopentanol (8e). In a
fashion similar to the synthesis of 8a, cyclopentanol (7) (86 mg, 1.0
mmol) reacted with 3-chlorobenzyl alcohol (3e) (285 mg, 2.0 mmol)
3) Martínez, R.; Ramon
987.
4) (a) Viciano, M.; Sanau,
́
050−6054. (b) Prades, A.; Viciano, M.; Sanau, M.; Peris, E.
́
, D. J.; Yus, M. Tetrahedron 2006, 62, 8982−
́
M.; Peris, E. Organometallics 2007, 26,
to afford 8e as a white solid (228 mg, 68% yield). Mp: 125−126 °C.
6
1
H NMR (CDCl , 400 MHz): δ 7.19 (m, 6 H, aromatic CH), 7.08 and
3
Organometallics 2008, 27, 4254−4259. (c) Gnanamgari, D.; Leung,
C. H.; Schley, N. D.; Hilton, S. T.; Crabtree, R. H. Org. Biomol. Chem.
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C. H.; Lau, C. P. Adv. Synth. Catal. 2008, 350, 2975−2983. (e) Chang,
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7.06 (s, 1:1 H, aromatic CH), 3.40 (m, 1 H, CHOH), 2.91 and 2.50 (q
each, 2:2 H, 2 × CH ), 2.02 (m, 2 H, 2 × CH), 1.74 and 1.28 (m each,
2
13
1
2
:3 H, 2 × CH and OH). C{ H} NMR (CDCl , 100 MHz): δ 143.2
2
3
and 134.3 (Cq each), 129.8, 129.1, 127.1, and 126.3 (aromatic CH),
8
3
3.2 (CHOH), 48.6, 39.7, and 27.0. HRMS: calcd for C H Cl O
34.0891, found 334.0881.
Synthesis of 2,5-Bis(2-chlorobenzyl)cyclopentanol (8f). In a
19 20 2
9
2
4
008. (g) Musa, S.; Ackermann, L.; Gelman, D. Adv. Synth. Catal.
013, 355, 3077−3080. (h) Bai, W.; Jia, G. C. Inorg. Chim. Acta 2015,
31, 234−241. (i) Jumde, V. R.; Gonsalvi, L.; Guerriero, A.; Peruzzini,
fashion similar to the synthesis of 8a, cyclopentanol (7) (86 mg, 1.0
mmol) reacted with 2-chlorobenzyl alcohol (3f) (285 mg, 2.0 mmol)
1
to afford 8f as a white solid (174 mg, 52% yield). Mp: 106−107 °C. H
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NMR (CDCl , 400 MHz): δ 7.25, 7.15, and 7.10 (m each, 2:2:4 H,
3
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×
CH ), 2.08 (m, 2 H, 2 × CH), 1.65 and 1.28 (m each, 2:3 H, 2 ×
2
13 1
́
Sanau, M.; Merino, S.; Tejeda, J.; Peris, E.; Royo, B. Organometallics
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2
3
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(
(
3
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19
20
2
34.0891, found 334.0884.
Synthesis of 2,5-Bis(2-fluorobenzyl)cyclopentanol (8g). In a
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13
1
2
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3
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5
1
.0 Hz, aromatic CH), 128.0 (d and Cq, J = 15.9 Hz, aromatic CH),
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DOI: 10.1021/acs.organomet.6b00130
Organometallics XXXX, XXX, XXX−XXX