Oxo-Rhenium-Catalyzed Radical Addition of Benzylic Alcohols to Olefins

Article abstract of DOI:10.1021/acs.joc.9b03150

Although carbon radicals generated from a variety of alcohol derivatives have proven valuable in coupling and addition reactions, the direct use of alcohols as synthetically useful radical sources is less known. In this report, benzylic alcohols are shown to be effective radical precursors for addition reactions to alkenes when treated with triphenylphosphine or piperidine with the catalyst ReIO₂(PPh₃)₂ (I).

Full text of DOI:10.1021/acs.joc.9b03150

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Article
Oxo-Rhenium-Catalyzed Radical Addition of Benzylic Alcohols to
Olefins
Chandrasekhar Bandari and Kenneth M. Nicholas*
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ABSTRACT: Although carbon radicals generated from a variety of alcohol derivatives
have proven valuable in coupling and addition reactions, the direct use of alcohols as
synthetically useful radical sources is less known. In this report, benzylic alcohols are
shown to be effective radical precursors for addition reactions to alkenes when treated with
triphenylphosphine or piperidine with the catalyst ReIO2(PPh3)2 (I).
dimers.20 Experimental and computational studies of the
rhenium-19,21 and vanadium-catalyzed22 reductive coupling
reactions point to the intermediacy of carbon radicals that are
generated by the facile homolytic C−O cleavage of reduced
metal−alkoxide intermediates. This novel transformation is a
rare example of C−C bond formation from alcohol substrates.
The established methods for generating alkyl radicals
typically employ alkyl halides, xanthates,23 oxalates,24 ben-
zoates,25 and phosphites26 as precursors, all of which are
prepared from the corresponding alcohols. Recently, alkylar-
enes,27 arylacetic acids,28 benzylamines,29 and benzylsilanes30
have also been demonstrated as benzylic radical sources.
However, the direct use of alcohols as C-radical precursors, as
implicated in the oxo−metal reductive coupling reactions
(Scheme 1B), and their application to C−C bond formation
are less known.31 In recent studies, low-valent titanium
reagents have been shown to stoichiometrically promote
reductive reactions of activated (benzylic and allylic) alcohols,
undergoing deoxygenation,32 dimerization to hydrocarbons,33
or addition to electron-deficient alkenes.34
INTRODUCTION
■
The search for sustainable transformations of oxygen-rich
renewable resources has stimulated widespread efforts to
discover and develop new reactions for the refunctionalization
and defunctionalization of alcohols and polyols.1 A recent
focus in the field of biomass conversion catalysis has been on
the deoxydehydration (DODH) of polyols, in which vicinal
hydroxyl groups are eliminated to produce unsaturated
products (Scheme 1A).1c DODH reactions are catalyzed by
Scheme 1. Reductive Deoxygenation of Glycols and Mono-
ols
Radical reactions that form C−C bonds by addition to
unsaturated substrates are well-known and useful processes in
organic synthesis.35−37 The ability of oxo−metal complexes to
activate C−O bonds in the DODH and reductive coupling of
alcohols prompted us to investigate and report here on their
ability to catalyze radical addition reactions of alcohols.
oxo-metal compounds of Re,2−4 Mo,5−8 and V,9 employing a
variety of reducing agents, including PPh3,2 H2,10,11 sulfite,12,13
secondary and benzylic alcohols,14−16 elements,17 and hydro-
aromatics.18
In recent studies, we discovered that benzylic and allylic
mono-alcohols undergo a novel reductive coupling reaction
with triphenylphosphine catalyzed by ReIO2(PPh3)2 (I)
(Scheme 1B).19 In contrast, oxovanadium complexes were
found to catalyze redox disproportionation of benzylic and
allylic alcohols (Scheme 1B), resulting in coproduction of
carbonyl products and the reductively coupled hydrocarbon
RESULTS AND DISCUSSION
■
We began the investigation examining the addition reaction
between benzyl alcohol (1A) and 1,1-diphenylethylene (DPE,
2A) in the presence of ReIO2(PPh3)2 (I) and PPh3 as reducing
Received: November 22, 2019
Published: January 22, 2020
https://dx.doi.org/10.1021/acs.joc.9b03150
© 2020 American Chemical Society
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Scheme 2. Optimization of the Benzyl Addition Reaction of DPE 2A
agent in benzene. The reaction was carried out under
The effectiveness of other potential reductants was also
evaluated (Table 2). Phosphines of varying steric and
conditions reported for the reductive couplingthat is, 0.2
M benzene at 150 °C in a sealed tube for 24 h. The addition
product 3A was isolated, albeit in low yield (10%), and
confirmed by spectroscopic analysis, accompanied by the
unexpected unsaturated product 3B (10%) (Scheme 2). At 1.0
M concentration of the reactants, the combined yield of 3A/
3B increased to 48% at 70% conversion (see the Supporting
Information, Table S1). Gas chromatography−mass spectrom-
etry (GC−MS) analysis of the reaction mixtures revealed the
coproduction of other benzyl alcohol derived byproducts,
including toluene, benzaldehyde, benzyl iodide (from
precatalyst), and bibenzyl, products observed in the reductive
coupling reactions (in the absence of alkene).19,21 Further
optimization studies evaluated the effects of reactant ratios on
the reaction efficiency (Table 1). The adduct yields were
Table 2. Survey of Prospective Reductants in the
a
Benzylation of Diphenylethylene
b
c
entry
reductant
P(o-Tol)3
P(C6H11)
PBu3
PPh2Me
Ph2PCH2CH2PPh2
(DPPE)
% conversion
% yield (3A + 3B)
1
2
3
4
5
87
92
50
55
0
35 (20 + 15)
40 (22 + 18)
14 (10 + 4)
44 (21 + 23)
0 (0 + 0)
6
7
8
9
pyridine
87
92
50
99
35 (20 + 15)
40 (22 + 18)
14 (10 + 4)
2,4,6-trimethylpyridine
4-dimethylaminopyridine
C5H11N (piperidine)
c
87 (55 + 32)
d
/83 (52 + 31)
Table 1. Reaction Optimization−Reactant Stoichiometry
10
11
C4H8NCH3
55
44 (21 + 23)
a
(1-methylpyrrolidine)
with PPh3 Reductant
e
isopropanol
95
95 (50 + 45)
1A
2A
(mmol)
PPh3
(mmol)
% yield
(3A + 3B)
a
b
c
BnOH (2.0 mmol), DPE 2A (1.0 mmol), reductantphosphine
entry (mmol)
% Conv.
(2.0 mmol), amine (1.0 mmol), or isopropanol (2.0 mmol), and
b
1
2
3
4
5
1.2
1.0
2.0
2.0
2.0
1.0
2.0
1.0
1.0
1.0
1.0
1.0
1.0
2.0
5.0
85
38 (23 + 19)
47 (25 + 22)
52 (31 + 21)
70 (44 + 26)
33 (20 + 13)
catalyst I (0.10 mmol) in 1.0 mL of benzene were heated at 150 °C
for 24 h. % conversion based on DPE 2A. Yield determined by
NMR with DMF as the internal standard. Isolated yield. 72 h
reaction time.
b
b
c
80
a
d
e
87
a
91
a
82
a
The indicated quantities of reactants and catalysts, ReIO2(PPh3)2 (I,
0.10 mmol), and 1.0 mL of benzene were heated in a sealed tube for
electronic characteristics were tested in the reaction (entries
1−5), but all were inferior to PPh3. Likely chelating DPPE
completely suppressed the reaction (entry 5), probably by
blocking alcohol coordination and activation. A number of
nitrogen-based prospective reductants were also tested (entries
6−10). Among these, the secondary amine piperidine gave the
best conversion and yield of the adducts (entry 9), 99 and
87%, respectively. GC−MS analysis showed that the major
piperidine-derived product detected was N-benzyl-piperidine;
OPPh3 and benzaldehyde were also found as oxidation
byproducts. The particular chemical role(s) played by
piperidine in these reactions, for example, a base, ligand, or
reductant, is yet unclear. Finally, isopropanol (2 mM) was also
found to be an effective but gradual, reductant for the
benzylation of DPE (entry 11).
The catalytic efficiency of a few commercially available oxo-
rhenium derivatives for the benzyl alcohol/DPE/piperidine
reaction was assessed under the standard conditions (Table 3,
entries 2−4). Only MeReO3 was used to afford a moderate
yield of the adducts. It was also found that decreasing the
loading of catalyst I to 5% slowed the reaction considerably,
decreasing the conversion and yield (Table 3, entry 5).
After developing the optimized reaction conditions for the
benzylation of DPE, the sensitivity of the reaction to the
b
c
24 h at 150 °C. % conversion based on the limiting reagent. Yield
determined by NMR with DMF as the internal standard.
modestly improved by employing an excess of either the alkene
(entry 1 vs 2) or the alcohol (entry 2 vs 3). The yield of 3A/B
was significantly improved to 70% by increasing the amount of
triphenylphosphine (entry 4), but a further increase to 5 equiv
suppressed both conversion and yield (entry 5). Several high
boiling solvents of low and medium polarity were also tested in
the reaction of Scheme 2 (at reflux or at 150 °C), but the
conversions and yields were inferior to those in benzene (see
the Supporting Information, Table S3).
Regarding the pathway to form the unsaturated product 3B,
the saturated product 3A was found to be unchanged when
heated at 150 °C with catalyst I and piperidine. Similarly, the
unsaturated product 3B was also unchanged under the same
conditions. These results show that the products do not
interconvert under the reaction conditions and suggest that
they are either formed by independent pathways or from a
common intermediate. This could be a result of disproportio-
nation of the intermediate benzyl radical adduct of DPE38 or
competing H-atom transfer from the intermediate radical by a
rhenium-hydroxo species (vide infra).
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requiring a longer reaction time to achieve complete
conversion. These results indicate that a moderate range of
electronic character of the benzylic alcohol is tolerated in the
reaction. A brief survey of the reactions between DPE and
some other activated alcohols (e.g., benzhydrol and allylic
alcohols) catalyzed by I typically afforded mostly the
hydrocarbon dimers derived from the alcohol and low yields
of the radical addition products (see the Supporting
Information, Scheme S1).
The scope of benzylation of various unsaturated substrates
was then evaluated using the optimized procedure with
piperidine as the reductant. The results are summarized in
Table 4 according to Scheme 3. A series of electron-deficient
Table 3. Effects of Catalyst and Its Loading on the Reaction
Efficiency and Selectivity
a
b
c
entry
Re-catalyst
% conversion
% yield (3A + 3B)
1
2
3
4
5
ReIO2(PPh3)2 (I)
NH4ReO4
Bu4NReO4
MeReO3
ReIO2(PPh3)2 (I)
99
35
0
80
45
87 (55 + 32)
12 (8 + 4)
0 (0 + 0)
56 (35 + 21)
22 (10 + 12)
d
a
BnOH (2.0 mmol), DPE 2A (1.0 mmol), piperidine (1.0 mmol), Re-
catalyst (10 mol %, 0.10 mmol), 1.0 mL of benzene, 150 °C in a
b
c
sealed tube, and 24 h. % Conversion based on DPE 2A. Yield
d
determined by NMR with DMF as the internal standard. 5 mol % I
(0.05 mmol) used under the same conditions as in .
a
Scheme 3. Substrate Scope of Rhenium-Catalyzed
Benzylation of Alkenes
electronic characteristic of the alcohol was investigated by
conducting reactions between DPE (2A) and a set of
electronically varied 4-substituted benzyl alcohols (Table 4,
entries 1−5). All five alcohols afforded moderate yields of a
mixture of saturated and unsaturated addition products. The
more electron-deficient alcohols 1C and 1E reacted gradually,
Table 4. Scope and Efficiency of Re-Catalyzed Benzylation of Alkenes
a
b
Alcohol (2.0 mmol), alkene (1.0 mmol), piperidine (1.0 mmol), I (0.1 mmol), 1.0 mL of benzene, 150 °C in a sealed tube, and 24 h. Isolated
c
d
e
f
yield following chromatography. 48 h reaction time. 5d reaction time. Mixture of diastereomers. 9:1 exo/endo.
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Scheme 4. Suggested Catalytic Cycle for Alcohol-Based Radical Addition to Alkene Catalyzed by ReIO2(PPh3)2 (I)
olefins (entries 6−12) were found to be suitable acceptors.
Diethyl fumarate reacted with benzyl alcohol (1:2) to give 2-
benzyldiethylsuccinate (3M) in 68% isolated yield (entry 6).
No unsaturated adduct was detected by GC−MS, but a small
amount of transesterification product (ca. 10−20%) was
indicated. Similarly, tert-butyl and benzyl acrylate underwent
Re-catalyzed addition producing the corresponding addition
products (3N and 3O) in 50 and 52% yield, respectively
(entries 7 and 8). Acrylonitrile gave the corresponding adduct
(3P) in only 20% yield after 48 h at 150 °C (entry 9), which
may be the result of competing thermal polymerization of this
sensitive alkene. On the other hand, N-benzyl maleimide was
converted to its benzylated derivative (3S) in moderate yield
(entry 12). In contrast to the above reactions, which gave
exclusively saturated addition products, C-3 benzylation of
coumarin was achieved in 80% yield while producing only the
unsaturated 3Q (entry 10). The benzyl radical apparently
attacks at the C3 of coumarin to generate the more stable
benzylic radical, probably followed by H-atom abstraction.39
Finally, an addition reaction between benzyl alcohol and the
strained 2-norbornene gave exo-benzyl norbornane (3T) as the
major product along with a small amount of the endo isomer
(9:1) in a moderate 62% combined yield (entry 13). Use of
isopropanol as a reductant with these alkenes gave inferior
conversion/yields. Screening reactions of BnOH with other
representative types of unsaturated substrates, e.g., vinyl ethers
(electron-rich), alkynes, diazenes, and imines, with piperidine/
I, typically showed little/no adduct formation but produced
rather bibenzyl, toluene, and benzaldehyde (see the Supporting
Information, Scheme S2), suggesting their low addition
reactivity with the relatively stable benzylic radicals.
Supported by our recent experimental and computational
studies of the reductive coupling of alcohols catalyzed by I,21
we suggest the operation of the catalytic pathway for the
radical additions outlined in Scheme 4. Beginning with alcohol
association with I, the O-transfer reduction of the Re(V)-
alkoxide II by PPh3 (or piperidine or BnOH) would produce
Re(III)-alcoholate III. Homolytic C−O bond scission of III
would give the Re(IV)-oxyl species IV and benzyl radical. Our
recent studies of the reductive coupling of benzylic (and
allylic) alcohols by the same reductant/catalyst combination,
PPh3/I, support the intermediacy of C-free radicals from: (1)
the product distribution-dimeric hydrocarbons (R−R) and/or
the reduced hydrocarbon (R−H);19 (2) the selectivity,
unsymmetrical allylic alcohols giving regioisomeric mixtures;19
(3) DFT-B3LYP computations that indicate a very low
Re(III,IV)O−R bond dissociation energy (20−25 kcal/
mol);21 and (4) the observed addition products and selectivity
in the current study, that is, the ready additions to EWG−
alkenes, consistent with the nucleophilic character of benzyl
radicals40 (and inconsistent with electrophilic intermediates,
e.g., carbocations). The C-radical can then be trapped by olefin
to give the adduct radical, which can either disproportionate38
(when alkene = diphenylethylene) or H-abstract from the Re-
OH species IV (for other alkenes) to give the reduced product
and regenerate I. We note that the enthalpy of this latter H-
transfer step is estimated to be quite favorable (ca. −47 kcal/
mol) by DFT/B3LYP computation.
CONCLUSIONS
■
The Re-catalyzed addition of alcohol-derived benzylic radicals
to olefins is an effective method for producing addition
products. The reactions are most efficient with electron-
deficient or strained alkenes. Our efforts are continuing to
expand the utility of metal-promoted C−O cleavage and C−C
bond-forming reactions with respect to the alcohol scope,
coupling partner, catalyst activity, and economy.
EXPERIMENTAL SECTION
■
General Information. All reactions were carried out in oven-
dried glassware unless otherwise specified. The reactants were
obtained commercially and used without further purification. Benzene
was distilled from sodium/benzophenone under nitrogen. Analytical
thin-layer chromatography was performed on silica gel plates (Merck
60F254) and visualized with a UV lamp (254 nm). Flash
1
chromatography was performed over silica gel (60−120 mesh). H
NMR spectra were recorded at 300 or 400 MHz in CDCl3 (unless
otherwise specified) at ambient temperature and processed using
MestReNova software; chemical shifts were given in parts per million
from tetramethylsilane with the solvent as an internal reference
(CDCl3 δ 7.26 ppm); 13C NMR spectra were recorded at 75 or 100
MHz in CDCl3 (unless otherwise specified), and the chemical shifts
were reported in parts per million from tetramethylsilane with the
solvent as an internal reference (CDCl3 δ 77.2 ppm); coupling
constants (J) were reported in Hertz (Hz). Gas chromatograms were
collected on a Shimadzu GC-2014 equipped with an AOC 20i+s
autosampler, with a 3% SE-54 packed column, and a FID detector.
GC−MS data were obtained using an Agilent 6890 N GC with 5973
MDS equipped with an Agilent HP-5 column (30 m × 250 μm × 0.25
μm). High-resolution mass spectrometry (HRMS) data and liquid
chromatography mass spectrometry data were obtained on an Agilent
6545-QTOF W/1290 high-performance liquid chromatography mass
spectrometer. Characterization data for previously reported com-
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pounds are given in the Supporting Information. ReIO2(Ph3P)2 (I)
was prepared efficiently by the reported method (below).41
6.23 (t, J = 7.6 Hz, 1H), 3.77 (s, 3H), 3.40 (d, J = 7.6 Hz, 2H);
13C{1H} NMR (100 MHz, CDCl3): δ 158.0, 142.3, 142.2, 139.9,
133.1, 130.0, 129.4, 128.4, 128.2, 127.4, 127.2, 127.1, 114.0, 35.1;
GCMS [M]+: 300.1.
Preparation of ReIO2(PPh3)2 (I). Sodium perrhenate (1.0 g, 3.7
mmol) and triphenylphosphine (5.0 g, 19 mmol) were added to a
mixture of 56% hydroiodic acid solution (5.0 mL) and ethanol (30
mL). The reaction was brought to reflux for 15 min. Green crystals of
ReI2O(OEt)(PPh3)2 formed in the mixture. After cooling to room
temperature, the crystals were filtered off, washed with ethanol, and
dried under high vacuum. To a mixture of acetone (50 mL) and water
(2 mL) was added ReI2O(OEt) (PPh3)2 (1.00 g, 0.97 mmol). The
green suspension was magnetically stirred at room temperature. After
an hour, the suspended crystals changed to violet color. The crystals
were filtered off and washed with cold acetone. The product was
recrystallized from hot 1:1 benzene/hexanes, giving an 80% yield of
ReIO2(PPh3)2 (I) (0.67 g, 0.78 mmol), which was stored in a
desiccator over CaCl2.
1,1-Diphenyl-3-(4-chlorophenyl)propane (3E).42 It is obtained
from 4-chlorobenzyl alcohol (1C) (285 mg, 2.0 mmol) and DPE
(2A) (0.18 mL, 0.18 g, 1.0 mmol) using the optimized general
procedure B isolated by column chromatography on silica gel with
ethyl acetate and hexane (1:20) to give the separable products (3E
1
and 3F, 1.2:1.0); 48 h, colorless oil (125 mg, 41% yield). H NMR
(300 MHz, CDCl3): δ 7.38−7.13 (m, 12H), 7.07 (d, J = 8.4 Hz, 2H),
3.90 (t, J = 7.7 Hz, 1H), 2.56 (dd, J = 9.2, 6.1 Hz, 2H), 2.43−2.27 (m,
2H); 13C{1H} NMR (100 MHz, CDCl3): δ 144.7, 140.6, 131.6,
129.9, 128.6, 128.5, 127.9, 126.4, 50.6, 37.3, 33.5; GCMS [M]+:
306.0.
1,1-Diphenyl-(3-(4-chlorophenyl)prop-1-ene (3F).29 48 h, color-
1
General Procedure A for the Addition of Benzyl Alcohol to
DPE. Benzyl alcohol (1A, 1−2 mmol, 1−2 equiv), DPE (2A, 1−2
mmol, 1−2 equiv), the reductant (1−2 mmol, 1−2 equiv), and
ReIO2(PPh3)2 (I) (87 mg, 0.10 mmol, 0.1 equiv) were mixed in 1.0
mL of dry benzene in a 10 mL thick-walled glass tube fitted with a
Teflon screw cap/plunger (Ace Glass) and a spin bar. The reaction
mixture was purged with nitrogen and heated at 150 °C in a
preheated silicone oil bath behind a blast shield for 24 h. The mixture
was cooled to room temperature, and an aliquot was removed for
less oil (103 mg, 34% yield). H NMR (400 MHz, CDCl3): δ 7.43−
7.30 (m, 2H), 7.27−7.20 (m, 10H) 7.10 (d, J = 8.4 Hz, 2H), 6.20 (t, J
= 7.6 Hz, 1H), 3.42 (d, J = 7.6 Hz, 2H); 13C{1H} NMR (100 MHz,
CDCl3): δ 143.1, 142.3, 139.7, 139.5, 131.9, 129.9, 129.8, 128.7,
128.5, 128.3, 127.5, 127.4, 127.3, 127.1, 35.4; GCMS [M]+: 304.0.
1,1-Diphenyl-3-(4-methylphenyl)propane (3G).42 It is obtained
from 4-methylbenzyl alcohol (1D) (244 mg, 2.0 mmol) and DPE
(2A) (0.18 mL, 0.18 g, 1.0 mmol) using the optimized general
procedure B isolated by column chromatography on silica gel with
ethyl acetate and hexane (1:19) to give the separable products (3G
1
analysis by H NMR spectroscopy, GC, and GC−MS. The percent
1
conversion and yield of the reaction were determined by NMR using
dimethylformamide (DMF) as an internal standard in CDCl3.
Integration of the reactant and product NMR peaks relative to the
DMF signals was used to determine the percent conversion and yield.
The addition products (3A and 3B) were isolated by column
chromatography (EtOAc/hexane 1:20) over silica gel eluting with
ethyl acetate and hexane and identified by comparison with the
spectra of known compounds.
and 3H, 1.0:1.0). 24 h, colorless oil (97 mg, 34% yield). H NMR
(300 MHz, CDCl3): δ 7.43−7.10 (m, 10H), 7.05 (q, J = 8.0 Hz, 4H),
3.91 (t, J = 7.7 Hz, 1H), 2.53 (dd, J = 9.4, 6.0 Hz, 2H), 2.40−2.33 (m,
2H), 2.31 (s, 3H); 13C{1H} NMR (75 MHz, CDCl3): δ 144.9, 139.4,
137.8, 129.0, 128.3, 127.9, 126.1, 50.6, 37.4, 33.6, 21.0; GCMS [M]+:
286.1.
1,1-Diphenyl-(3-(4-methylphenyl)prop-1-ene (3H).29 24 h, color-
1
less oil (97 mg, 34% yield). H NMR (300 MHz, CDCl3): δ 7.41−
1,1,3-Triphenylpropane (3A).42 Colorless oil (141 mg, 52% yield).
1H NMR (400 MHz, CDCl3): δ 7.61 (ddd, J = 12.0, 8.3, 1.4 Hz, 2H),
7.15 (m, 10H), 7.13−6.95 (m, 4H), 6.25 (t, J = 7.6 Hz, 1H), 3.43 (d,
J = 7.6 Hz, 2H), 2.32 (s, 3H). 13C{1H} NMR (75 MHz, CDCl3): δ
142.5, 142.2, 139.8, 139.0, 135.5, 129.9, 129.2, 128.5, 128.3, 128.1,
127.3, 127.1, 127.0, 35.5, 21.0; GCMS [M]+: 284.1.
7.55−7.32 (m, 3H), 7.33−6.94 (m, 10H), 3.86 (t, J = 7.7 Hz, 1H),
2.51 (dd, J = 9.3, 6.3 Hz, 2H), 2.39−2.25 (m, 2H); 13C{1H} NMR
(75 MHz, CDCl3): 144.9, 142.2, 128.6, 128.5, 128.4, 128.0, 126.3,
125.9, 50.8, 37.4, 34.2; GCMS [M]+: 272.1.
1,1-Diphenyl-3-(4-fluorophenyl)propane (3I).42 It is obtained
from 4-fluorobenzyl alcohol (1E) (0.23 mL, 0.25 g, 2.0 mmol) and
DPE (2A) (0.18 mL, 0.18 g, 1.0 mmol) using the optimized general
procedure B isolated by column chromatography on silica gel with
ethyl acetate and hexane (1:19) to give the separable products (3I and
1,1,3-Triphenyl-prop-1-ene (3B).29 Colorless oil (84 mg, 31%
yield). 1H NMR (400 MHz, CDCl3): δ 7.48−7.10 (m, 15H), 6.28 (t,
J = 7.6 Hz, 1H), 3.49 (d, J = 7.6 Hz, 2H); 13C{1H} NMR (100 MHz,
CDCl3): δ 142.6, 142.5, 141.1, 139.9, 130.1, 128.6, 128.5, 128.4,
128.2, 127.9, 127.4, 127.3, 127.2, 126.1, 36.1; GCMS [M]+: 270.1.
Optimized General Procedure B for the Addition Reaction
to Alkenes. The alcohol (2.0 mmol, 2 equiv), the alkene (1.0 mmol,
1.0 equiv), ReIO2(PPh3)2 I (87 mg, 0.10 mmol, 0.1 equiv), and
piperidine (0.10 mL, 85 mg, 1.0 mmol, 1.0 equiv) were mixed in dry
benzene (1 mL) in a 5 mL thick-walled glass tube fitted with a Teflon
screw cap/plunger (Ace Glass) and a spin bar. The reaction mixture
was purged with nitrogen and heated at 150 °C in a preheated silicone
oil bath. The mixture was cooled to room temperature, and an aliquot
was removed for analysis by GC and GC−MS. The resulting mixture
was separated by column chromatography over silica gel eluting with
ethyl acetate and hexane to give the desired addition products (3C−
3T).
1
3J, 0.7:1.0). 5d, Colorless oil (74 mg, 26% yield). H NMR (300
MHz, CDCl3): δ 7.47−6.86 (m, 14H), 3.90 (t, J = 7.7 Hz, 1H), 2.55
(dd, J = 9.3, 6.1 Hz, 2H), 2.43−2.26 (m, 2H); 13C{1H} NMR (75
MHz, CDCl3): δ 163.0, 144.8, 137.7, 129.8, 128.6, 128.0, 126.4,
115.3, 50.7, 37.6, 33.4. GCMS [M]+: 290.1.
1,1-Diphenyl-(3-(4-fluorophenyl)prop-1-ene (3J).29 5d, Colorless
1
oil (106 mg, 36% yield). H NMR (300 MHz, CDCl3): δ 7.44−7.21
(m, 10H), 7.19−7.10 (m, 2H), 7.02−6.94 (m, 2H), 6.23 (t, J = 7.6
Hz, 1H), 3.50−3.37 (d, J = 7.6 Hz, 2H); 13C{1H} NMR (75 MHz,
CDCl3): δ 142.8, 142.4, 139.8, 136.7, 136.6, 130.0, 129.9, 129.8,
128.5, 128.3, 127.6, 127.6, 127.4, 127.3, 127.3, 115.5, 115.2, 35.2;
GCMS [M]+: 288.1.
1,1-Diphenyl-3-(2,4-dichlorophenyl)propane (3K). It is obtained
from 2,4-dichlorobenzyl alcohol (1F) (354 mg, 2.0 mmol) and DPE
(2A) (0.18 mL, 0.18 g, 1.0 mmol) using the optimized general
procedure B (5 d) isolated by column chromatography on silica gel
with ethyl acetate and hexane (3:97) to give the separable products
1,1-Diphenyl-3-[(4-methoxyphenyl)]propane (3C).42 It is ob-
tained from 4-methoxybenzyl alcohol (1B) (276 mg, 2.0 mmol)
and DPE (2A) (0.18 mL, 0.18 g, 1.0 mmol) using the optimized
general procedure B isolated by column chromatography on silica gel
with ethyl acetate and hexane (1:20) to give the product as a mixture
(3C and 3D). 24 h, colorless oil (220 mg, 73% yield) 3C/3D (1.5:1).
1H NMR (400 MHz, CDCl3): δ 7.40−7.00 (m, 12H) 6.92−6.67 (m,
1
(3K and 3L, 1.6:1.0). Colorless oil (163 mg, 48% yield). H NMR
(300 MHz, CDCl3): δ 7.37−7.21 (m, 9H), 7.21−7.08 (m, 3H), 7.03
(d, J = 8.2 Hz, 1H), 3.93 (t, J = 7.8 Hz, 1H), 2.76−2.48 (m, 2H),
2.44−2.20 (m, 2H); 13C{1H} NMR (75 MHz, CDCl3): δ 144.5,
138.5, 134.7, 132.3, 131.3, 129.4, 128.7, 127.9, 127.1, 126.4, 51.2,
35.5, 32.0; GCMS [35‑Cl, 35‑ClM]+: 340.1, [35‑Cl, 37‑ClM]+: 342.1,
2H), 3.89 (t, J = 7.7 Hz, 1H), 3.77 (s, 3H), 2.50 (dd, J = 9.2, 6.2 Hz,
2H), 2.3−2.30 (m, 2H); 13C{1H} NMR (100 MHz, CDCl3): δ 157.8,
144.9, 134.2, 129.4, 128.6, 128.0, 126.2, 113.8, 55.3, 50.6, 37.6, 33.2;
GCMS [M]+: 302.1.
[
37‑Cl, 37‑ClM]+: 344.1. The compound did not ionize by ESI−MS,
preventing acquisition of HRMS.
1,1-Diphenyl-3-(4-methoxyphenyl)prop-1-ene (3D).29 24 h,
1,1-Diphenyl-(3-(2,4-dichlorophenyl)prop-1-ene (3L). Colorless
1
1
colorless oil. H NMR (400 MHz, CDCl3): δ 7.40−7.0 (m, 14H),
oil (102 mg, 30% yield). H NMR (300 MHz, CDCl3): δ 7.47−
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Article
6.95 (m, 13H), 6.19 (t, J = 7.5 Hz, 1H), 3.52 (d, J = 7.5 Hz, 2H);
13C{1H} NMR (75 MHz, CDCl3): δ 143.9, 142.2, 139.6, 137.3, 134.7,
132.6, 131.0, 129.9, 129.3, 128.5, 128.3, 127.5, 127.4, 127.2, 125.4,
125.3, 33.3; GCMS [M]+: 338.1; HRMS (ESI-TOF) m/z: [M − H]−
calcd for C21H15Cl2, 337.0556; found, 337.0547.
1,3-Dibenzylpyrrolidine-2,5-dione (3S).47 It is obtained from
benzyl alcohol (1A) (0.21 mL, 0.22 g, 2.0 mmol) and N-
benzylpyrrolidine-2,5-dione (2H) (187 mg, 1.0 mmol) using the
optimized general procedure B isolated by column chromatography
on silica gel with ethyl acetate and hexane (1:10) to give the product
(3S); 48 h, pale yellow oil (82 mg, 32% yield). 1H NMR (300 MHz,
CDCl3): δ 7.38−7.16 (m, 7H), 7.16−7.03 (m, 3H), 4.62 (s, 2H),
3.23−3.03 (m, 2H), 2.96−2.80 (m, 1H), 2.69 (dd, J = 18.4, 8.9 Hz,
1H), 2.51−2.34 (m, 1H); 13C{1H} NMR (100 MHz, CDCl3): δ
179.1, 176.1, 136.9, 135.7, 129.1, 128.9, 128.8, 128.7, 128.0, 127.1,
42.5, 41.3, 36.4, 33.2; GCMS [M]+: 279.1.
Diethyl 2-Benzylsuccinate (3M).43 It is obtained from benzyl
alcohol (1A) (0.21 mL, 0.22 g, 2.0 mmol) and diethyl fumarate (2B)
(0.17 mL, 0.17 g, 1.0 mmol) using the optimized general procedure B
isolated by column chromatography on silica gel with ethyl acetate
and hexane (1:10) to give the product 3M; 24 h, colorless oil (179
mg, 68% yield). 1H NMR (300 MHz, CDCl3): δ 7.38−7.07 (m, 5H),
4.11 (q, J = 7.1 Hz, 2H), 4.09 (q, J = 7.1 Hz, 2H), 3.18−2.95 (m,
2H), 2.84−2.56 (m, 2H), 2.48−2.28 (m, 1H), 1.22 (t, J = 7.1 Hz,
3H), 1.19 (t, J = 7.1 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3): δ
174.4, 171.9, 138.3, 129.1, 128.6, 126.7, 60.8, 60.7, 43.2, 37.9, 35.3,
14.2, 14.2; GCMS [M]+: 264.1.
2-Benzylbicyclo[2.2.1]heptane (3T).48 It is obtained from benzyl
alcohol (1A) (0.21 mL, 0.22 g, 2.0 mmol) and norbornene (2I) (94
mg, 1.0 mmol) using the optimized general procedure B isolated by
column chromatography on silica gel with ethyl acetate and hexane
(1:20) to give the product (3T); 48 h, colorless oil (115 mg, 62%
yield) (exo isomer/endo isomer 9/1, data for major isomer). 1H
NMR (300 MHz, CDCl3): δ 7.38−7.02 (m, 5H), 2.55 (dd, J = 13.7,
8.3 Hz, 1H), 2.42 (dd, J = 13.6, 7.4 Hz, 1H), 2.30−2.13 (m, 1H),
2.06−1.90 (m, 1H), 1.75 (qd, J = 7.9, 4.5 Hz, 1H), 1.65−0.81 (m,
8H); 13C{1H} NMR (75 MHz, CDCl3): δ 142.0, 129.1, 128.3, 125.7,
43.8, 42.9, 40.5, 38.0, 36.9, 35.2, 30.2, 29.0; GCMS [M]+: 186.1.
Thermal Stability Test of 1,1,3-Triphenylpropane (3A) in
the Presence of Catalyst I/Piperidine. 1,1,3-Triphenylpropane 3A
(54 mg, 0.20 mmol), ReIO2(PPh3)2 (I) (17 mg, 0.020 mmol), and
piperidine (20 μL, 0.20 mmol) were mixed in dry benzene (0.2 mL)
in a 2 mL thick-walled glass tube fitted with a Teflon screw cap/
plunger (Ace Glass) and a spin bar. The reaction mixture was purged
with nitrogen and heated at 150 °C in a preheated silicone oil bath for
24 h. The mixture was cooled to room temperature, and an aliquot
tert-Butyl-4-phenylbutanoate (3N).44 It is obtained from benzyl
alcohol (1A) (0.21 mL, 0.22 g, 2.0 mmol) and tert-butyl acrylate (2C)
(0.15 mL, 0.13 g, 1.0 mmol) using the optimized general procedure B
isolated by column chromatography on silica gel with ethyl acetate
and hexane (1:10) to give the product 3N; 24 h, colorless oil (110
mg, 50% yield). 1H NMR (300 MHz, CDCl3): δ 7.39−7.34 (m, 1H),
7.33−7.27 (m, 1H), 7.23−7.15 (m, 3H), 2.74−2.53 (m, 2H), 2.24 (t,
J = 7.5 Hz, 2H), 2.00−1.80 (m, 2H), 1.45 (s, 9H); 13C{1H} NMR
(100 MHz, CDCl3): δ 173.0, 141.7, 128.6, 128.4, 126.0, 80.2, 35.2,
35.0, 28.2, 26.9; GCMS [M]+: 220.1.
Benzyl-4-phenylbutanoate (3O).45 It is obtained from benzyl
alcohol (1A) (0.21 mL, 0.22 g, 2.0 mmol) and benzyl acrylate (2D)
(0.16 mL, 0.16 g, 1.0 mmol) using the optimized general procedure B
isolated by column chromatography on silica gel with ethyl acetate
and hexane (1:10) to give the product (3O); 24 h, pale yellow oil
(132 mg, 52% yield). 1H NMR (400 MHz, CDCl3): δ 7.42−7.21 (m,
10H), 5.12 (s, 2H), 2.65 (t, J = 7.5 Hz, 2H), 2.39 (t, J = 7.5 Hz, 2H),
1.99 (quin, J = 7.5 Hz, 2H); 13C{1H} NMR (100 MHz, CDCl3): δ
173.5, 141.5, 136.1, 128.7, 128.6, 128.5, 128.4, 128.3, 126.1, 66.3,
35.2, 33.7, 26.6; GCMS [M]+: 254.1.
1
was removed for analysis by H NMR spectroscopy, GC, and GC−
MS.
Stability Test of 1,1,3-Triphenylprop-1-ene (3B) in the
Presence of I/Piperidine. 1,1,3-Triphenyl-prop-1-ene 3B (54.0
mg, 0.20 mmol), ReIO2(PPh3)2 (I) (17 mg, 0.020 mmol), and
piperidine (20 μL, 0.20 mmol) were mixed in dry benzene (0.2 mL)
in a 2 mL thick-walled glass tube fitted with a Teflon screw cap/
plunger (Ace Glass) and a spin bar. The reaction mixture was purged
with nitrogen and heated at 150 °C in a preheated silicone oil bath for
24 h. The mixture was cooled to room temperature, and an aliquot
4-Phenylbutanenitrile (3P).46 It is obtained from benzyl alcohol
(1A) (0.21 mL, 0.22 g, 2.0 mmol) and acrylonitrile (2E) (60 μL, 1.0
mmol) using the optimized general procedure B isolated by column
chromatography on silica gel with ethyl acetate and hexane (1:20) to
1
was removed for analysis by H NMR spectroscopy, GC, and GC−
1
give the product (3P); 48 h, pale yellow oil (29 mg, 20% yield). H
MS.
NMR (300 MHz, CDCl3): δ 7.39−7.08 (m, 5H), 2.79 (t, J = 7.4 Hz,
2H), 2.33 (t, J = 7.4 Hz, 2H), 2.01 (quin, J = 7.4 Hz, 2H). 13C{1H}
NMR (75 MHz, CDCl3): δ 139.8, 128.8, 128.6, 126.7, 119.7, 34.5,
27.1, 16.5; GCMS [M]+: 145.1.
ASSOCIATED CONTENT
■
sı
* Supporting Information
3-Benzyl-2H-chromen-2-one (3Q).39 It is obtained from benzyl
alcohol (1A) (0.21 mL, 0.21 g, 2.0 mmol) and coumarin (2F) (146
mg, 1.0 mmol) using the optimized general procedure B isolated by
column chromatography on silica gel with ethyl acetate and hexane
(1:10) to give the product (3Q); 24 h, white solid (188 mg, 80%
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.joc.9b03150.
Reaction procedures, reaction optimization studies, and
characterization data for reaction products (1H NMR
spectra, unit resolution GC−mass spectra, HRMS, and
13C NMR data for new compounds) (PDF)
1
yield). H NMR (300 MHz, CDCl3): δ 7.48−7.44 (t, J = 7.6 Hz, 1
H), 7.38−7.28 (m, 8 H), 7.24−7.20 (t, J = 7.6 Hz, 1 H), 3.90 (s, 2 H)
ppm; 13C{1H} NMR (75 MHz, CDCl3): δ 161.5, 152.9, 139.2, 137.5,
130.7, 129.3, 129.2, 128.6, 127.3, 126.7, 124.2, 119.3, 116.2, 36.4;
GCMS [M]+: 236.1.
AUTHOR INFORMATION
3-Benzyl-2-methyl-5-(prop-1-en-2-yl)cyclohexan-1-one (3R). It is
obtained from benzyl alcohol (1A) (0.21 mL, 0.22 g, 2.0 mmol) and
S-carvone (2G) (0.15 mL, 0.15 g, 1.0 mmol) using the optimized
general procedure B (48 h) isolated by column chromatography on
silica gel with ethyl acetate and hexane (1:10) to give the product
(3R) as a mixture of stereoisomers; pale yellow oil (148 mg, 61%
yield). IR (KBr) 3084, 3062, 3026, 2970, 2933, 1710, 1645, 1602,
■
Corresponding Author
Kenneth M. Nicholas − Department of Chemistry and
Biochemistry, University of Oklahoma, Norman, Oklahoma
73019, United States; orcid.org/0000-0002-5180-1671;
Email: knicholas@ou.edu
1
1494, 1452, 1377, 1217, 1029, 893, 748, 732, 702 cm−1; H NMR
Author
(300 MHz, CDCl3): δ 7.37−7.00 (m, 5H), 4.85−4.57 (m, 2H),
2.97−2.04 (m, 7H), 2.03−1.42 (m, 5H), 1.17 (dd, J = 19.5, 6.8 Hz,
3H); 13C{1H} NMR (75 MHz, CDCl3): δ 213.8, 212.9, 147.4, 146.9,
140.3, 140.0, 129.4, 129.2, 128.9, 128.5, 128.5, 126.2, 111.4, 110.0,
49.5, 48.5, 46.3, 43.8, 43.3, 42.2, 40.9, 40.8, 40.5, 40.2, 36.1, 33.3,
32.5, 30.9, 21.4, 20.8, 14.5, 12.1; GCMS [M]+: 242.2; HRMS (ESI-
TOF) m/z: [M + H]+ calcd for C17H23O, 243.1749; found, 243.1760.
Chandrasekhar Bandari − Department of Chemistry and
Biochemistry, University of Oklahoma, Norman, Oklahoma
73019, United States
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.joc.9b03150
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(18) Boucher-Jacobs, C.; Nicholas, K. M. Oxo-Rhenium-Catalyzed
Deoxydehydration of Polyols with Hydroaromatic Reductants.
Organometallics 2015, 34, 1985−1990.
Notes
The authors declare no competing financial interest.
(19) Kasner, G. R.; Boucher-Jacobs, C.; McClain, J. M.; Nicholas, K.
M. Oxo-rhenium catalyzed reductive coupling and deoxygenation of
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ACKNOWLEDGMENTS
■
The authors are grateful for the support of this project from
the National Science Foundation (CHE 1566213)
(20) Steffensmeier, E.; Nicholas, K. M. Oxidation−reductive
coupling of alcohols catalyzed by oxo-vanadium complexes. Chem.
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(22) Steffensmeier, E.; Swann, M. T.; Nicholas, K. M. Mechanistic
Features of the Oxidation−Reductive Coupling of Alcohols Catalyzed
by Oxo-Vanadium Complexes. Inorg. Chem. 2019, 58, 844−854.
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