N-heterocyclic carbene catalyzed carba-, sulfa-, and phospha-Michael additions with NHC·CO2 adducts as precatalysts

Article abstract of DOI:10.1021/jo500108a

N-heterocyclic carbene catalyzed Michael additions have been revisited with 1,3-dialkyl- or 1,3-diarylimidazol(in)ium-2-carboxylates, that is, NHC·CO₂ adducts, as the source of the free NHC catalysts in solution. Using these precatalysts, a number of efficient carba-, sulfa-, and phospha-Michael additions were achieved very conveniently, without the need for an external strong base to generate the NHC by deprotonation of an azolium salt. To further expand the scope of the procedure, some NHC-catalyzed sulfa-Michael/aldol organocascades were also investigated.

Full text of DOI:10.1021/jo500108a

Note
pubs.acs.org/joc
N‑Heterocyclic Carbene Catalyzed Carba‑, Sulfa‑, and Phospha-
Michael Additions with NHC·CO2 Adducts as Precatalysts
Morgan Hans,† Lionel Delaude,*,† Jean Rodriguez,*,‡ and Yoann Coquerel*,‡
†Laboratory of Organometallic Chemistry and Homogeneous Catalysis, Institut de chimie (B6a), Universite
4000 Liege, Belgium
‡Aix Marseille Universite,
́ ̀
de Liege, Sart-Tilman par
̀
́
Centrale Marseille, CNRS, iSm2 UMR 7313, 13397 Marseille, France
S
* Supporting Information
ABSTRACT: N-heterocyclic carbene catalyzed Michael addi-
tions have been revisited with 1,3-dialkyl- or 1,3-
diarylimidazol(in)ium-2-carboxylates, that is, NHC·CO2 ad-
ducts, as the source of the free NHC catalysts in solution.
Using these precatalysts, a number of efficient carba-, sulfa-,
and phospha-Michael additions were achieved very conven-
iently, without the need for an external strong base to generate
the NHC by deprotonation of an azolium salt. To further
expand the scope of the procedure, some NHC-catalyzed sulfa-Michael/aldol organocascades were also investigated.
-heterocyclic carbenes (NHCs) have found widespread
intermolecular reactions and some stereoselective Michael/
Napplications in organometallic chemistry and organic Michael/aldol organocascades with various kinds of Michael
acceptors (Scheme 1b,c).18 Concurrently, NHC-catalyzed oxa-
synthesis. Because of their excellent σ-donor properties, NHCs
have primarily been used as ancillary ligands in transition-metal
Michael19 and aza-Michael20 additions were performed using
imidazolium salt precatalysts in the presence of a strong base
and in some cases a stoichiometric additive (Scheme 1d,e).
Because sulfa-21 and phospha-Michael22,23 additions are among
the most effective methods to synthesize organo-sulfur and
organo-phosphorus compounds, the development of general,
practical, and efficient catalytic systems to ease these reactions
is of great importance. Herein, we disclose that NHC-catalyzed
carba-, sulfa-, and phospha-Michael additions were efficiently
accomplished with readily available and very convenient to use
imidazol(in)ium-2-carboxylate (NHC·CO2) precatalysts
(Scheme 1f).
Relatively air-stable NHC·CO2 zwitterions can be prepared
by trapping either preformed or in situ generated 1,3-
disubstituted imidazol(in)-2-ylidenes with carbon dioxide
(Scheme 2).24,25 The reaction is reversible in solution, and
the carboxylate adducts were shown to act as convenient
sources of free NHC ligands for the stoichiometric preparation
of NHC−transition-metal complexes with concomitant release
of carbon dioxide.26−29 In contrast, only a few NHC-catalyzed
organocatalytic transformations taking advantage of NHC·CO2
precatalysts have been described so far. Known examples
include transesterification reactions,30−32 the cyclotrimerization
of isocyanates,33 the benzoin condensation,31,32 the cyanosily-
lation of carbonyl compounds,32 and some related polymer-
ization reactions.32,34,35 In 2012, it was also demonstrated that
imidazol(in)ium hydrogen carbonates behaved as alternate
sources of NHCs upon formal loss of H2CO3.32,36
complexes for homogeneous catalysis, which resulted in the
development of a number of metal-based catalysts with
enhanced and unique properties.1,2 Alternatively, NHCs have
also been used on their own as organocatalysts in a variety of
transformations.3−5 In this field, three distinct organocatalytic
activation modes were identified: (1) ambiphilic activation,
which results from the simultaneous σ-donor and π-acceptor
properties of NHCs and allows them to trigger catalytic
“umpolung” reactivity with aldehydes and enals,6,7 (2)
nucleophilic activation when NHCs are used as Lewis base
(σ-donor) catalysts, for example in NHC-catalyzed trans-
esterification reactions,8 Morita−Baylis−Hillman reactions,9
formal cycloadditions of zwitterionic enolate equivalents,10,11
and polymerization reactions,12 and (3) Brønsted base
activation, the least studied path, which relies on the ability
of NHCs to operate as catalytic proton shuttles as in the case of
NHC-catalyzed Michael additions (Scheme 1). Of course, the
reactivity and organocatalytic properties of NHCs are strongly
dependent on their steric and electronic properties.13 Among
the four common classes of NHCs (Figure 1), imidazolinyli-
denes and imidazolylidenes are the most potent Brønsted bases,
with pKa values of the corresponding azolium salts ranging
between 20 and 25 in aqueous solutions,14,15 while
thiazolylidenes and triazolylidenes exhibit significantly lower
Brønsted basicity with pKa values of ca. 15−19 for thiazolium
and triazolium salts in water.16
In 2009, stable and isolated imidazolylidenes were found to
catalyze intramolecular Michael additions with high efficiency
for the stereoselective synthesis of spiro compounds (Scheme
1a).17 This organocatalytic system was successfully extended to
Received: January 21, 2014
© XXXX American Chemical Society
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Note
a
Scheme 1. NHC-Catalyzed Michael Additions
Scheme 2. NHC·CO2 Adducts Used in This Study
Table 1. NHC-Catalyzed Michael Additions with NHC·CO2
a
Precatalysts
b
entry
EWG
NHC·CO2
product
yield (%)
1
2
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
SO2Ph
SO2Ph
CN
1a
1a
1a
1a
1a
1a
1b
1b
1c
1c
≤1
80
47
64
6
IDipp·CO2
SIDipp·CO2
IMes·CO2
SIMes·CO2
ICy·CO2
IDipp·CO2
ICy·CO2
IDipp·CO2
ICy·CO2
3
4
5
6
100
88
93
21
88
7
8
9
10
CN
a
Reaction conditions: methyl 2-oxocyclopentanecarboxylate (0.25
mmol), electrophile (0.30 mmol), NHC·CO2 (5 mol %), anhydrous
b
1
THF (2.5 mL), 14 h at 21 °C. Determined by H NMR analysis
(single-scan experiments) with naphthalene as internal standard.
and in sharp contrast with previous results obtained for Michael
additions catalyzed by free NHCs,18 a test reaction in
dichloromethane with IDipp·CO2 (2.5 mol %) failed to afford
the Michael adduct 1a after 12 h at room temperature (no
reaction), reflecting the greater stability of the carboxylate
precatalyst in this solvent. A control experiment also confirmed
that the reaction did not proceed in the absence of any catalyst
(Table 1, entry 1). Further investigations showed that
imidazolylidene·CO2 adducts were better promoters of the
Michael addition than the corresponding imidazolinylidene·
CO2 adducts (compare entry 2 with 3, and 4 with 5) and that
the N,N′-dialkyl NHC·CO2 adduct ICy·CO2 was more efficient
than the N,N′-diaryl derivatives (compare entry 6 with entries
2−5, entry 8 with entry 7, and entry 10 with entry 9). Previous
work had established that isolated imidazolylidenes were better
catalysts for the Michael addition than the corresponding
saturated NHCs (imidazolinylidenes)17,18 and that imidazoly-
lidene·CO2 adducts were less stable, and thus more prone to
release the free carbenes, than the corresponding imidazoliny-
lidene·CO2 adducts.25,28 Results in Table 1 (entries 2−5) are
fully consistent with these earlier findings. In addition, it was
also reported that N,N′-dialkylimidazol(in)ylidenes were better
Brønsted bases than N,N′-diarylimidazol(in)ylidenes.15 Hence,
a
Abbreviations: Dipp, 2,6-(iPr)2-C6H3; Mes, 2,4,6-(Me)3-C6H2; Cy,
cyclohexyl; EWG, electron-withdrawing group; KHMDS, potassium
hexamethyldisilazide.
Figure 1. The four common classes of NHCs and their relative
Brønsted basicities.
The present study was initiated with the assessment of the
organocatalytic activities of five representative NHC·CO2
adducts in model carba-Michael additions (Table 1). It was
shown earlier that the reversible decomposition of NHC·CO2
adducts into the corresponding NHCs and carbon dioxide was
relatively rapid in polar aprotic solvents,28 and a brief screening
of solvents allowed us to identify THF as a suitable and
convenient medium for the studied transformations. Notably,
B
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Note
the superior catalytic activity of the NHC derived from ICy·
CO2 in the Michael addition (entries 6, 8, and 10) was
attributed to the enhanced basicity of ICy in comparison to the
other NHCs under investigation. For the sake of comparison, a
mixture of 1,3-dicyclohexylimidazolium tetrafluoroborate and
potassium hexamethyldisilazide was also employed to generate
the NHC ICy (5 mol %). This system afforded product 1a
quantitatively, as did ICy·CO2 under similar conditions (Table
1, entry 6). No attempt was made to perform the reaction with
the free carbene ICy, because this NHC is particularly difficult
to isolate in pure form.37 Overall, these results demonstrate that
NHC·CO2 adducts are indeed good precatalysts for NHC-
catalyzed Michael additions and ICy·CO2 was singled out as
the most potent one among the five representative zwitterions
investigated. The advantages of using an NHC·CO2 adduct
instead of an azolium salt precatalyst or an isolated free carbene
are essentially practical: the carboxylate inner salts can be easily
prepared on a 10 g scale, stored for extended periods of time,
and used directly without additives when needed. With an
azolium salt precatalyst, the corresponding NHC must be
generated by in situ deprotonation, which is particularly
inconvenient when a base-free or salt-free reaction medium is
required, while the free carbenes are usually much more
sensitive to oxygen and moisture and require stringent
conditions.
provided the corresponding sulfa-Michael adducts 2g,h in high
yields (entries 8 and 9, respectively). To demonstrate the
scalability of the process, a gram-scale synthesis of product 2b
was carried out starting from thiophenol (10 mmol) and
acrylonitrile (12 mmol) in the presence of ICy·CO2 (2.5 mol
%). With no other modification to the procedure outlined
above than the substrate concentration (1 M instead of 0.1 M),
3-(phenylsulfanyl)propanenitrile was isolated in 96% yield after
chromatographic purification. Also particularly worth noting are
the reactions of 2-aminobenzenethiol and pyridine-2-thiol with
methyl vinyl ketone (3a), which chemoselectively afforded the
corresponding sulfa-Michael adducts 2i,j in 98% and 78%
yields, respectively (Scheme 3). In the latter case, however, a
Scheme 3. S/N Chemoselectivity in NHC-Catalyzed Hetero-
Michael Additions
Next, the attention was turned to the NHC-catalyzed sulfa-
Michael addition using ICy·CO2 as the precatalyst in THF
(Table 2). In these experiments, thiophenol served as a model
minor amount (ca. 15%) of the aza-Michael addition product
N-2j was produced. It was shown previously that the NHC-
catalyzed hetero-Michael addition of 2-aminoethanol to an α,β-
unsaturated ketone led only to the aza-Michael addition
product.20 Thus, the chemoselectivity of NHC-catalyzed
hetero-Michael additions follows the order RSH > RNH2 >
ROH.
Table 2. NHC-Catalyzed Sulfa-Michael Additions with the
ICy·CO2 Precatalyst
a
b
entry
R
R’
EWG
product
yield (%)
Some sulfa-Michael/aldol organocascades were previously
reported under aminocatalytic conditions.38 Hence, with an
efficient catalytic system at hand for the sulfa-Michael addition,
NHC-catalyzed sulfa-Michael-initiated organocascades were
investigated. The reaction of methyl 2-mercaptoacetate (4a)
with methyl vinyl ketone (3a) or acrolein (3b) in the presence
of ICy·CO2 (2.5 mol %) in THF gave the expected
tetrahydrothiophenes 5a,b in good yields, albeit with a poor
diastereoselectivity (Scheme 4). Another type of sulfa-Michael/
aldol organocascade also proved possible using 1,4-dithiane-2,5-
diol (4b), a dimeric surrogate of 2-mercaptoacetaldehyde, in
combination with methyl vinyl ketone (3a). In the presence of
ICy·CO2 (2.5 mol %) in THF, the corresponding tetrahy-
c
d
1
Ph
Ph
Ph
Ph
Ph
Ph
Ph
H
H
H
H
H
H
Ph
H
H
CO2tBu
CO2tBu
CN
2a
2a
2b
2c
2d
2e
2f
≤1
2
3
4
90
e
99
SO2Ph
CONH2
COMe
COPh
COMe
COMe
90
78
98
99
99
93
f
5
6
g
7
8
9
2-naphthyl
allyl
2g
2h
a
Reaction conditions: thiol (0.25 mmol), electrophile (0.30 mmol),
ICy·CO2 (2.5 mol %, except for entries 1, 5, and 7), anhydrous THF
b
(2.5 mL), 2 h at 21 °C. After silica gel chromatography (except for
c
d
entry 1). Reaction performed without precatalyst. Based on 1H
e
NMR analysis of the crude reaction mixture. A gram-scale reaction
afforded product 2b in 96% yield. Reaction performed with 10 mol %
of ICy·CO2. Reaction performed with 5 mol % of ICy·CO2.
f
Scheme 4. NHC-Catalyzed Sulfa-Michael/Aldol
Organocascades with the ICy·CO2 Precatalyst
g
nucleophile, whose reaction was investigated with a variety of
electrophiles (entries 1−7). A blank test performed without any
precatalyst confirmed that the uncatalyzed reaction did not
occur (or proceeded very slowly) under the experimental
conditions adopted (entry 1). In the presence of a catalytic
amount of ICy·CO2, however, generally high yields of the sulfa-
Michael adducts 2a−f were obtained under the standard
conditions used throughout this study (21 °C, 2 h) with α,β-
unsaturated ester, nitrile, sulfone, amide, and ketone derivatives.
Reactions with naphthalene-2-thiol and propene-1-thiol also
C
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Note
drothiophene 5c was isolated in excellent yield, but the
diastereoselectivity remained modest (Scheme 4).
initiated organocascades were also carried out. Importantly, it
was demonstrated that zwitterionic imidazolium carboxylates,
the so-called NHC·CO2 adducts, are excellent and very
convenient sources of the corresponding free NHCs in solution
for NHC-catalyzed Michael additions. The main advantages of
using NHC·CO2 adducts are that they can be easily prepared
on a multigram scale and stored for extended periods of time,
they can be handled and weighed in the air, and most
importantly, they do not require the use of an external strong
base or any additive to generate the corresponding NHCs. This
last feature proved critical in the present study because, unlike
the NHC IDipp used in the early NHC-catalyzed Michael
additions (see Scheme 1), its ICy congener, which was found
most efficient at promoting the (hetero)Michael additions
detailed herein, is difficult to isolate in pure form and is usually
generated in situ by deprotonation of an imidazolium salt.
From a broader perspective, it is our belief that NHC·CO2
adducts will soon be recognized as attractive precatalysts for the
development of organocatalysis with NHCs.
The same catalytic system was also applied to the phospha-
Michael addition of two prototypical phosphorus-based
pronucleophiles, namely diphenylphosphine oxide (6a) and
diethylphosphonic acid (6b). It was recently demonstrated that
diphenylphosphine oxide (6a) could undergo phospha-Michael
additions to terminal and internal activated alkenes upon
thermal activation (neat, microwave-assisted heating at ca.
125−200 °C).39,40 Indeed, the uncatalyzed reaction of 6a with
tert-butyl acrylate at 21 °C for 2 h afforded only traces of the
corresponding phospha-Michael adduct 7a (Table 3, entry 1).
Table 3. NHC-Catalyzed Phospha-Michael Additions with
a
the ICy·CO2 Precatalyst
b
entry
R
R’
EWG
ICy·CO2 (mol %) product yield (%)
EXPERIMENTAL SECTION
■
c
1
Ph
H
H
H
H
H
H
Ph
H
H
H
H
H
H
CO2tBu
CO2tBu
CN
0
10
5
7a
7a
7b
7c
7d
7e
7f
≤2
76
General Information. Reactions were performed under an air
atmosphere using 10 mL tubular oven-dried reaction vessels equipped
with a Teflon-coated magnetic stirring bar and capped with a rubber
septum. Imidazol(in)ium-2-carboxylates were prepared according to
the literature.28 All other reagents were obtained from commercial
sources and were used as supplied unless otherwise specified.
Anhydrous THF was obtained from a solvent purification system.
Thiophenol and 2-propene-1-thiol were dried over CaCl2 and distilled
prior to use. All acrylic acid derivatives were filtered through a short
pad of silica gel prior to use, except phenyl vinyl sulfone, acrylamide,
and trans-chalcone. All reagents and precatalysts were weighed and
handled in air at room temperature. The reactions were monitored by
TLC visualized by UV (254 nm) and/or with p-anisaldehyde/H2SO4
in EtOH and/or molybdophosphoric acid in EtOH. Column
chromatography was performed with silica gel. Petroleum ether refers
to the fraction distilled at 40−60 °C. 1H, 13C{1H}, and 31P{1H} NMR
spectra were recorded at 298 K in CDCl3 or CD2Cl2, using either
tetramethylsilane (δ 0.00 ppm) or the residual nondeuterated solvent
2
Ph
3
Ph
82
84
4
Ph
SO2Ph
CONH2
COMe
COPh
CO2tBu
CO2tBu
CN
5
c
5
Ph
10
5
0
6
Ph
81
75
7
Ph
10
0
c
8
OEt
OEt
OEt
OEt
OEt
OEt
8a
8a
8b
8c
8d
8e
0
9
2.5
99
99
97
10
11
12
13
2.5
2.5
SO2Ph
CONH2
COMe
c
10
2.5
0
98
a
Reaction conditions: diphenylphosphine oxide (6a) or diethylphos-
phonic acid (6b, 0.25 mmol), electrophile (0.30 mmol), ICy·CO2 (2.5
mol %), anhydrous THF (2.5 mL), 2 h at 21 °C. After silica gel
chromatography (except for entries 1, 5, 8, and 12). Based on H
NMR analysis of the crude reaction mixture.
b
c
1
1
signal for H NMR (δ 7.26 ppm for CHCl3 and δ 5.32 for CD2Cl2)
and the deuterated solvent signal for 13C NMR (δ 77.16 ppm for
CHCl3 and δ 53.84 for CD2Cl2) as internal standards or H3PO4 (δ
0.00 ppm) as external reference for 31P NMR. Coupling constants (J)
are given in hertz, and the classical abbreviations are used to describe
the signal multiplicity. For 13C{1H} NMR experiments, the signal
multiplicity with hydrogen atoms (C, CH or CH3, CH2) was
determined by DEPT-135 experiments.
Gratifyingly, the same reaction performed in the presence of a
catalytic amount of ICy·CO2 (10 mol %) afforded product 7a
in 76% yield (entry 2). The screening of other representative
electrophiles in the presence of 5−10 mol % of ICy·CO2
helped define the scope of the reaction. Thus, activation of the
alkene with a cyanide (entry 3), a sulfone (entry 4), or a ketone
moiety (entries 6 and 7) were successful, but the reaction with
acrylamide, a generally poor electrophile for (hetero)Michael
addition reactions, failed to afford the desired product 7d
(entry 5). With 6b as the pronucleophile, the reactions with the
same representative electrophilic alkenes were found to be even
more efficient than with 6a, requiring only 2.5 mol % of the
precatalyst to obtain nearly quantitative yields of the isolated
phospha-Michael adducts 8a−c,e after 2 h at 21 °C (entries 9−
11 and 13, respectively). Again, acrylamide was found to be
inert under these experimental conditions (entry 12).
In summary, the scope of NHC-catalyzed Michael additions
has been extended to their sulfa and phospha analogues, which
nicely complements the organocatalytic applications of NHCs
involving a Brønsted base activation mode. The simplicity and
efficiency of the method makes it an attractive alternative to
known procedures for sulfa-21 and phospha-Michael22,23
additions. Additionally, some NHC-catalyzed sulfa-Michael-
General Procedure for Carba-Michael Additions (Table 1).
The reaction vessel was charged with the NHC·CO2 adduct (0.0126
mmol, 5 mol %; see Table 1) and naphthalene (0.25 mmol, 32 mg).
Anhydrous THF (2.5 mL), methyl 2-oxocyclopentanecarboxylate
(0.25 mmol, 31 μL), and the acrylic acid derivative (0.30 mmol) were
then added in that order. The reaction mixture was stirred at 21 °C for
14 h and concentrated under vacuum, and the resulting material was
directly analyzed by NMR spectroscopy (in CDCl3). The yield of
Michael addition products 1a−c was determined by comparing the
integrals of the product resonances (single-scan experiments) with
those of naphthalene (7.63 and 7.26 ppm). The NMR data recorded
for products 1a−c were identical with previously reported data.18
Control Experiment with an Imidazolium Precatalyst. An
NMR tube was charged with ICy·HBF4 (0.005 mmol, 1.6 mg),
potassium bis(trimethylsilyl)amide (0.005 mmol, 1.0 mg), and
naphthalene (0.10 mmol, 12.8 mg) as an internal standard. Anhydrous
deuterated THF (1 mL) was added, and the mixture was shaken at 21
°C for 5 min. Methyl 2-oxocyclopentanecarboxylate (0.10 mmol, 12.4
μL) and methyl acrylate (0.12 mmol, 10.8 μL) were then added in that
1
order. The NMR tube was shaken periodically. After 14 h, the H
D
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Note
NMR analysis of the reaction mixture indicated full conversion (no
more starting material) and a quantitative yield of 1a by comparing the
integrals of the product resonances with those of naphthalene.
General Procedure for Sulfa-Michael Additions (Table 2 and
Scheme 3). The reaction vessel was charged with ICy·CO2 (0.0063
mmol, 2.5 mol %, 1.7 mg). Anhydrous THF (2.5 mL), the thiol (0.25
mmol), and the acrylic acid derivative (0.30 mmol) were then added in
that order. The reaction mixture was stirred at 21 °C for 2 h and
concentrated under vacuum, and the resulting material was directly
purified by silica gel chromatography with petroleum ether/EtOAc (7/
3 v/v) as eluent to afford the pure products 2a−j.
CH3), 127.4 (CH or CH3), 48.3 (CH2), 44.8 (CH or CH3). These
NMR data matched previously reported data.42
4-(Naphthylsulfanyl)butan-2-one (2g). Off-white solid (57 mg,
99%) obtained from naphthalene-2-thiol (40 mg) and methyl vinyl
ketone (3a, 24 μL). 1H NMR (300 MHz, CDCl3, ppm): δ 7.81−7.74
(m, 4H), 7.51−7.41 (m, 3H), 3.24 (t, J = 7.3 Hz, 2H), 2.79 (t, J = 7.3
Hz, 2H), 2.13 (s, 3H). 13C{1H} NMR (75 MHz, CDCl3, ppm): δ
206.6 (C), 133.8 (C), 133.3 (C), 131.9 (C), 128.6 (CH or CH3),
127.8 (CH or CH3), 127.5 (CH or CH3), 127.3 (CH or CH3), 127.1
(CH or CH3), 126.7 (CH or CH3), 125.9 (CH or CH3), 43.1 (CH2),
30.1 (CH or CH3), 27.3 (CH2). These NMR data matched previously
reported data.45
tert-Butyl 3-(Phenylsulfanyl)propanoate (2a). Colorless oil (54
mg, 90%) obtained from thiophenol (26 μL) and tert-butyl acrylate
4-(Allylsulfanyl)butan-2-one (2h). Colorless oil (34 mg, 93%)
1
(44 μL). H NMR (300 MHz, CDCl3, ppm): δ 7.28−7.08 (m, 5H),
obtained from 2-propene-1-thiol (21 μL) and methyl vinyl ketone (3a,
1
3.04 (t, J = 7.4 Hz, 2H), 2.44 (t, J = 7.4 Hz, 2H), 1.36 (s, 9H).
13C{1H} NMR (75 MHz, CDCl3, ppm): δ 171.1 (C), 135.7 (C), 130.0
(CH or CH3), 129.1 (CH or CH3), 126.5 (CH or CH3), 81.0 (C),
35.6 (CH2), 29.3 (CH2), 28.2 (CH or CH3). These NMR data
matched previously reported data.41
24 μL). H NMR (300 MHz, CDCl3, ppm): δ 5.82−5.72 (m, 1H),
5.13−5.07 (m, 2H), 3.13 (d, J = 7.1 Hz, 2H), 2.68 (m, 4H), 2.15 (s,
3H). 13C{1H} NMR (75 MHz, CDCl3, ppm): δ 206.9 (C), 134.4 (CH
or CH3), 117.3 (CH2), 43.6 (CH2), 35.2 (CH2), 30.2 (CH or CH3),
24.6 (CH2). These NMR data matched previously reported data.46
4-(2-Aminophenylsulfanyl)butan-2-one (2i). Light yellow oil (48
mg, 98%) obtained from 2-aminothiophenol (27 μL) and methyl vinyl
3-(Phenylsulfanyl)propanenitrile (2b). Colorless oil (41 mg, 99%)
obtained from thiophenol (26 μL) and acrylonitrile (20 μL). 1H NMR
(300 MHz, CDCl3, ppm): δ 7.35−7.18 (m, 5H), 3.03 (t, J = 7.3 Hz,
2H), 2.50 (t, J = 7.3 Hz, 2H). 13C{1H} NMR (75 MHz, CDCl3, ppm):
δ 133.3 (C), 131.5 (CH or CH3), 129.4 (CH or CH3), 127.8 (CH or
CH3), 118.0 (C), 30.3 (CH2), 18.3 (CH2). These NMR data matched
previously reported data.42 A gram-scale experiment was also
performed as follows: a 50 mL oven-dried round-bottom flask was
charged with ICy·CO2 (0.25 mmol, 69 mg), anhydrous THF (10 mL),
thiophenol (10.0 mmol, 1.03 mL), and acrylonitrile (12 mmol, 0.79
mL), in that order. The reaction mixture was stirred at 21 °C for 2 h
and concentrated under vacuum, and the resulting material was
directly purified by silica gel chromatography with petroleum ether/
EtOAc (7/3 v/v) as eluent to afford the pure product 2b (1.57 g,
96%).
1
ketone (3a, 24 μL). H NMR (300 MHz, CD2Cl2, ppm): δ 7.35 (m,
1H), 7.12 (m, 1H), 6.74−6.64 (m, 2H), 4.44 (br s, 2H), 2.92 (t, J =
7.0 Hz, 2H), 2.66 (t, J = 7.0 Hz, 2H), 2.09 (s, 3H). 13C{1H} NMR (75
MHz, CD2Cl2, ppm): δ 207.1 (C), 149.4 (C), 136.6 (CH or CH3),
130.5 (CH or CH3), 118.7 (CH or CH3), 117.3 (C), 115.3 (CH or
CH3), 43.6 (CH2), 30.3 (CH or CH3), 28.8 (CH2). HRMS (ESI+):
m/z [M + H]+ calcd for C10H14NOS+ 196.0791, obsd 196.0791.
4-(2-Pyridinesulfanyl)butan-2-one (2j) and 4-(2-Thiopyridinyl)-
butan-2-one (N-2j). Yellow oil (42 mg, 92%) obtained from pyridine-
2-thiol (28 mg) and methyl vinyl ketone (3a, 24 μL) containing a
5.7:1 mixture of 2j and N-2j that could not be separated by silica gel
1
chromatography. H NMR (300 MHz, CDCl3, ppm): major isomer
(2j), δ 8.37 (m, 1H), 7.43 (m, 1H), 7.11 (m, 1H), 6.94 (m, 1H), 3.34
(t, J = 7.0 Hz, 2H), 2.88 (t, J = 7.0 Hz, 2H), 2.13 (s, 3H); minor
isomer (N-2j), δ 7.90 (m, 1H), 7.61 (m, 1H), 7.13 (m, 1H), 6.59 (m,
1H), 4.67 (t, J = 5.8 Hz, 2H), 3.22 (t, J = 5.8 Hz, 2H), 2.11 (s, 3H).
13C{1H} NMR (75 MHz, CDCl3, ppm): major isomer (2j), δ 207.1
(C), 158.6 (C), 149.5 (CH or CH3), 135.9 (CH or CH3), 122.4 (CH
or CH3), 119.4 (CH or CH3), 43.8 (CH2), 30.1 (CH or CH3), 23.7
(CH2); minor isomer (N-2j), δ 206.4 (C), 179.6 (C), 142.4 (CH or
CH3), 136.4 (CH or CH3), 134.2 (CH or CH3), 113.2 (CH or CH3),
52.0 (CH2), 40.8 (CH2), 30.4 (CH or CH3). HRMS (ESI+): m/z [M
+H]+ calcd for C9H12NOS+ 182.0634, obsd 182.0634.
General Procedure for Sulfa-Michael/Aldol Organocascades
(Scheme 4). The reaction vessel was charged with ICy·CO2 (1.7 mg,
0.0063 mmol). Anhydrous THF (2.5 mL), methyl 2-mercaptoacetate
(4a, 22 μL, 0.25 mmol) or 1,4-dithiane-2,5-diol (4b, 18.9 mg, 0.125
mmol), and methyl vinyl ketone (3a, 24 μL, 0.30 mmol) or acrolein
(3b, 20 μL, 0.30 mmol) were then added in that order. The reaction
mixture was stirred at 21 °C for 2 h (with 4a) or 24 h (with 4b). After
concentration under vacuum, the resulting material was purified by
filtration through a pad of silica gel with CH2Cl2/EtOAc (1/1 v/v) as
eluent to afford the pure compounds 5a−c as mixtures of
diastereomers.
Methyl 3-Hydroxy-3-methyltetrahydrothiophene-2-carboxylate
(5a). Pale yellow oil (37 mg, 84%) obtained from methyl 2-
mercaptoacetate (4a, 22 μL) and methyl vinyl ketone (3a, 24 μL)
as a 1/1 mixture of diastereomers. 1H NMR (250 MHz, CDCl3, ppm):
δ 3.81 (s, 1H), 3.74 (s, 3H), 3.70 (s, 3H), 3.68 (s, 1H), 3.17−3.09 (m,
1H), 3.06−3.00 (m, 2H), 2.86−2.79 (m, 1H), 2.37−2.25 (m, 2H),
2.10−2.02 (m, 1H), 1.94−1.85 (m, 1H), 1.45 (s, 3H), 1.41 (s, 3H).
13C{1H} NMR (63 MHz, CDCl3, ppm): δ 173.2 (C), 172.9 (C), 82.9
2-(Phenylsulfanyl)ethyl Phenyl Sulfone (2c). White solid (62 mg,
90%) obtained from thiophenol (26 μL) and phenyl vinyl sulfone (50
1
mg). H NMR (300 MHz, CDCl3, ppm): δ 7.78 (m, 2H), 7.57 (m,
1H), 7.47 (m, 2H), 7.20−7.10 (m, 5H), 3.25−3.16 (m, 2H), 3.13−
3.04 (m, 2H). 13C{1H} NMR (75 MHz, CDCl3, ppm): δ 138.7 (C),
134.1 (CH or CH3), 133.5 (C), 130.2 (CH or CH3), 129.5 (CH or
CH3), 129.4 (CH or CH3), 128.1 (CH or CH3), 127.3 (CH or CH3),
55.7 (CH2), 26.5 (CH2). These NMR data matched previously
reported data.43
3-(Phenylsulfanyl)propanamide (2d). White solid (35 mg, 78%)
obtained from thiophenol (26 μL) and acrylamide (17.8 mg) using 10
mol % of catalyst (6.8 mg, 0.0252 mmol). 1H NMR (300 MHz,
CDCl3, ppm): δ 7.37−7.34 (m, 2H), 7.31−7.26 (m, 2H), 7.22−7.17
(m, 1H), 5.75 (br s, 2H), 3.19 (t, J = 7.3 Hz, 2H), 2.51 (t, J = 7.3 Hz,
2H). 13C{1H} NMR (75 MHz, CDCl3, ppm): δ 173.2 (C), 135.2 (C),
129.9 (CH or CH3), 129.3 (CH or CH3), 126.7 (CH or CH3), 35.5
(CH2), 29.4 (CH2). These NMR data matched previously reported
data.42
4-(Phenylsulfanyl)butan-2-one (2e). Colorless oil (44 mg, 98%)
obtained from thiophenol (26 μL) and methyl vinyl ketone (3a, 24
μL). 1H NMR (300 MHz, CDCl3, ppm): δ 7.36−7.27 (m, 4H), 7.22−
7.17 (m, 1H), 3.14 (t, J = 7.3 Hz, 2H), 2.76 (t, J = 7.3 Hz, 2H), 2.14
(s, 3H). 13C{1H} NMR (75 MHz, CDCl3, ppm): δ 206.6 (C), 135.8
(C), 129.6 (CH or CH3), 129.1 (CH or CH3), 126.4 (CH or CH3),
43.1 (CH2), 30.1 (CH or CH3), 27.5 (CH2). These NMR data
matched previously reported data.44
1,3-Diphenyl-3-(phenylsulfanyl)propan-1-one (2f). White solid
(79 mg, 99%) obtained from thiophenol (26 μL) and trans-chalcone
1
(52 mg) using 5 mol % of catalyst (3.4 mg, 0.0126 mmol). H NMR
(300 MHz, CDCl3, ppm): δ 7.87−7.84 (m, 2H), 7.53−7.48 (m, 1H),
7.42−7.31 (m, 6H), 7.26−7.14 (m, 6H), 4.96 (dd, J = 6.4 Hz, J = 7.8
Hz, 1H), 3.65 (dd, J = 17.2 Hz, J = 7.8 Hz, 1H), 3.56 (dd, J = 17.2 Hz,
J = 6.4 Hz, 1H). 13C{1H} NMR (75 MHz, CDCl3, ppm): δ 197.0 (C),
141.3 (C), 136.8 (C), 134.3 (C), 133.3 (CH or CH3), 132.8 (2 CH or
CH3), 128.9 (2 CH or CH3), 128.7 (2 CH or CH3), 128.5 (2 CH or
CH3), 128.1 (2 CH or CH3), 127.9 (2 CH or CH3), 127.6 (CH or
(C), 81.0 (C), 59.0 (CH or CH3), 54.2 (CH or CH3), 52.6 (CH or
CH3), 52.4 (CH or CH3), 43.3 (CH2), 41.4 (CH2), 29.2 (CH2), 28.9
(CH2), 25.4 (CH or CH3), 22.1 (CH or CH3). HRMS (ESI+): m/z
[M + Li]+ calcd for C7H12O3SLi+ 183.0662, obsd 183.0661. See the
Supporting Information for NMR spectra.
Methyl 3-Hydroxytetrahydrothiophene-2-carboxylate (5b). Pale
yellow oil (34 mg, 84%) obtained from methyl 2-mercaptoacetate (4a,
E
dx.doi.org/10.1021/jo500108a | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
1
22 μL) and acrolein (3b, 20 μL) as a 3/1 mixture of diastereomers. 1H
NMR (250 MHz, CDCl3, ppm): major diastereomer, δ 4.60 (m, 1H),
3.98 (d, J = 4.4 Hz, 1H), 3.76 (s, 3H), 3.20−3.10 (m, 1H), 2.98−2.90
(m, 1H), 2.36−2.26 (m, 1H), 2.06−1.94 (m, 1H); minor
diastereomer, δ 4.68 (m, 1H), 3.82 (d, J = 3.4 Hz, 1H), 3.71 (s,
3H), 3.25−3.15 (m, 1H), 2.95−2.86 (m, 1H), 2.33−2.23 (m, 1H),
2.02−1.92 (m, 1H). 13C{1H} NMR (63 MHz, CDCl3, ppm): major
diastereomer, δ 172.8 (C), 75.0 (CH or CH3), 52.7 (CH or CH3),
51.1 (CH or CH3), 37.0 (CH2), 29.2 (CH2); minor diastereomer, δ
172.7 (C), 76.7 (CH or CH3), 54.5 (CH or CH3), 52.6 (CH or CH3),
37.3 (CH2), 28.8 (CH2). HRMS (ESI+): m/z [M + Li]+ calcd for
C6H10O3SLi+ 169.0505, obsd 169.0506.
methyl vinyl ketone (3a, 24 μL) using ICy·CO2 (3.4 mg). H NMR
(250 MHz, CDCl3, ppm): δ 7.74−7.67 (m, 4H), 7.50−7.41 (m, 6H),
2.79−2.69 (m, 2H), 2.56−2.46 (m, 2H), 2.08 (s, 3H). 13C{1H} NMR
(63 MHz, CDCl3, ppm): δ 206.2 (d, J = 13.4 Hz, C), 132.4 (d, J =
100.0 Hz, C), 132.1 (d, J = 2.7 Hz, CH or CH3), 130.8 (d, J = 9.4 Hz,
CH or CH3), 128.8 (d, J = 11.7 Hz, CH or CH3), 35.3 (d, J = 2.4 Hz,
CH2), 29.8 (s, CH or CH3), 23.3 (d, J = 73.7 Hz, CH2). 31P{1H}
NMR (101.3 MHz, CDCl3, ppm): δ 31.55. These NMR data matched
previously reported data.39
1,3-Diphenyl-3-(diphenylphosphinyl)propan-1-one (7f). White
solid (67 mg, 65%) obtained from diphenylphosphine oxide (6a,
50.5 mg) and trans-chalcone (52.1 mg) using ICy·CO2 (6.8 mg). H
1
NMR (250 MHz, CDCl3, ppm): δ 8.03−7.94 (m, 2H), 7.85−7.82 (m,
2H), 7.54−7.27 (m, 10H), 7.26−7.09 (m, 6H), 4.51−4.43 (m, 1H),
4.08−3.95 (m, 1H), 3.45−3.32 (m, 1H). 13C{1H} NMR (63 MHz,
CDCl3, ppm): δ 196.8 (d, J = 13.3 Hz, C), 136.5 (d, J = 0.6 Hz, C),
136.1 (d, J = 5.6 Hz, C), 133.5 (s, CH or CH3), 132.1 (d, J = 2.7 Hz,
CH or CH3), 131.6 (d, J = 94.4 Hz, C), 131.55 (s, CH or CH3), 131.5
(s, CH or CH3), 131.4 (s, CH or CH3), 131.1 (d, J = 8.9 Hz, CH or
CH3), 130.0 (d, J = 5.7 Hz, CH or CH3), 129.1 (d, J = 11.2 Hz, CH or
CH3), 128.7 (s, CH or CH3), 128.4 (s, CH or CH3), 128.3 (s, CH or
CH3), 128.2 (s, CH or CH3), 128.1 (s, CH or CH3), 127.2 (d, J = 2.4
Hz, CH or CH3), 41.2 (d, J = 69.1 Hz, CH or CH3), 39.2 (s, CH2).
31P{1H} NMR (101.3 MHz, CDCl3, ppm): δ 34.27. These NMR data
matched previously reported data.48
3-Acetyl-4-hydroxytetrahydrothiophene (5c). Pale yellow oil (36
mg, 98%) obtained from 1,4-dithiane-2,5-diol (4b, 18.9 mg) and
methyl vinyl ketone (3a, 24 μL) as a 1.7/1 mixture of diastereomers.
1H NMR (250 MHz, CDCl3, ppm): major diastereomer, δ 4.82 (br s,
1H), 3.24−2.71 (m, 6H), 2.27 (s, 3H); minor diastereomer, δ 4.62−
4.49 (m, 1H), 3.24−2.71 (m, 6H), 2.23 (s, 3H). 13C{1H} NMR (63
MHz, CDCl3, ppm): major diastereomer, δ 207.6 (C), 75.0 (CH or
CH3), 60.8 (CH or CH3), 39.6 (CH2), 30.3 (CH or CH3), 28.9
(CH2); minor diastereomer, δ 207.8 (C), 76.0 (CH or CH3), 61.0
(CH or CH3), 37.0 (CH2), 29.6 (CH or CH3), 29.1 (CH2). HRMS
(ESI+): m/z [M + Li]+ calcd for C6H10O2SLi+ 153.0556, obsd
153.0555.
General Procedure for Phospha-Michael Additions (Table
3). The reaction vessel was charged with ICy·CO2 (1.7, 3.4, or 6.8 mg,
0.0063, 0.0126, or 0.0252 mmol, respectively; see Table 3). Anhydrous
THF (2.5 mL), diphenylphosphine oxide (6a, 50.5 mg, 0.25 mmol) or
diethylphosphonic acid (6b, 32 μL, 0.25 mmol), and the acrylic acid
derivative (0.30 mmol) were then added in that order. The reaction
mixture was stirred at 21 °C for 2 h and concentrated under vacuum,
and the resulting material was directly purified by silica gel
chromatography with CH2Cl2/EtOAc (1/1 v/v) as eluent to afford
the pure product 7a−c,e,f from 6a or with EtOAc to isolate 8a−c,e
from 6b.
tert-Butyl 3-(Diethoxyphosphinyl)propanoate (8a). Colorless oil
(66 mg, 99%) obtained from diethylphosphonic acid (6b, 32 μL) and
1
tert-butyl acrylate (44 μL) using ICy·CO2 (1.7 mg). H NMR (250
MHz, CDCl3, ppm): δ 4.04 (m, 4H), 2.45 (m, 2H), 1.97 (m, 2H),
1.39 (s, 9H), 1.27 (t, J = 7.0 Hz, 6H). 13C{1H} NMR (63 MHz,
CDCl3, ppm): δ 171.3 (d, J = 18.9 Hz, C), 81.0 (s, C), 61.7 (d, J = 6.4
Hz, CH2), 28.7 (d, J = 3.8 Hz, CH2), 28.1 (s, CH or CH3), 21.1 (d, J =
144.3 Hz, CH2), 16.5 (d, J = 6.0 Hz, CH or CH3). 31P{1H} NMR
(101.3 MHz, CDCl3, ppm): δ 31.16. These NMR data matched
previously reported data.49
3-(Diethoxyphosphinyl)propanenitrile (8b). Colorless oil (47.3
tert-Butyl 3-(Diphenylphosphinyl)propanoate (7a). White solid
mg, 99%) obtained from diethylphosphonic acid (6b, 32 μL) and
(63 mg, 76%) obtained from diphenylphosphine oxide (6a, 50.5 mg)
1
1
acrylonitrile (20 μL). H NMR (250 MHz, CDCl3, ppm): δ 4.11 (m,
and tert-butyl acrylate (44 μL) using ICy·CO2 (6.8 mg). H NMR
4H), 2.60 (m, 2H), 2.05 (m, 2H), 1.32 (t, J = 7.1 Hz, 6H). 13C{1H}
NMR (63 MHz, CDCl3, ppm): δ 118.4 (d, J = 17.6 Hz, C), 62.4 (d, J
= 6.5 Hz, CH2), 22.2 (d, J = 145.9 Hz, CH2), 16.5 (d, J = 5.9 Hz, CH
or CH3), 11.6 (d, J = 4.0 Hz, CH2). 31P{1H} NMR (101.3 MHz,
CDCl3, ppm): δ 25.90. These NMR data matched previously reported
data.50
(250 MHz, CDCl3, ppm): δ 7.78−7.69 (m, 4H), 7.51−7.45 (m, 6H),
2.62−2.46 (m, 4H), 1.38 (s, 9H). 13C{1H} NMR (63 MHz, CDCl3,
ppm): δ 171.7 (d, J = 17.2 Hz, C), 132.6 (d, J = 99.4 Hz, C), 132.0 (d,
J = 2.8 Hz, CH or CH3), 130.9 (d, J = 9.4 Hz, CH or CH3), 128.8 (d, J
= 11.7 Hz, CH or CH3), 81.2 (s, C), 28.1 (s, CH or CH3), 27.6 (d, J =
2.1 Hz, CH2), 25.1 (d, J = 73.1 Hz, CH2). 31P{1H} NMR (101.3 MHz,
CDCl3, ppm): δ 31.52. These NMR data matched previously reported
data.47
2-(Diethoxyphosphinyl)ethyl Phenyl Sulfone (8c). White solid (74
mg, 97%) obtained from diethylphosphonic acid (6b, 32 μL) and
1
phenyl vinyl sulfone (50 mg). H NMR (250 MHz, CDCl3, ppm): δ
3-(Diphenylphosphinyl)propanenitrile (7b). White solid (52 mg,
7.86 (m, 2H), 7.69−7.53 (m, 3H), 4.05 (m, 4H), 3.26 (m, 2H), 2.10
(m, 2H), 1.26 (t, J = 7.1 Hz, 6H). 13C{1H} NMR (63 MHz, CDCl3,
ppm): δ 138.2 (s, C), 134.2 (s, CH or CH3), 129.6 (s, CH or CH3),
128.2 (s, CH or CH3), 62.4 (d, J = 6.6 Hz, CH2), 50.3 (d, J = 3.5 Hz,
CH2), 19.7 (d, J = 143.5 Hz, CH2), 16.4 (d, J = 5.9 Hz, CH or CH3).
31P{1H} NMR (101.3 MHz, CDCl3, ppm): δ 26.28. These NMR data
matched previously reported data.51
4-(Diethoxyphosphinyl)butan-2-one (8e). Colorless oil (51 mg,
98%) obtained from diethylphosphonic acid (6b, 32 μL) and methyl
vinyl ketone (3a, 24 μL). 1H NMR (250 MHz, CDCl3, ppm): δ 4.13−
4.01 (m, 4H), 2.77−2.67 (m, 2H), 2.16 (s, 3H), 2.06−1.91 (m, 2H),
1.30 (t, J = 7.1 Hz, 6H). 13C{1H} NMR (63 MHz, CDCl3, ppm): δ
205.9 (d, J = 15.0 Hz, C), 61.8 (d, J = 6.4 Hz, CH2), 36.5 (d, J = 3.8
Hz, CH2), 29.8 (s, CH or CH3), 19.5 (d, J = 144.7 Hz, CH2), 16.5 (d,
J = 6.1 Hz, CH or CH3). 31P{1H} NMR (101.3 MHz, CDCl3, ppm): δ
31.49. These NMR data matched previously reported data.52
82%) obtained from diphenylphosphine oxide (6a, 50.5 mg) and
acrylonitrile (20 μL) using ICy·CO2 (3.4 mg). H NMR (250 MHz,
1
CDCl3, ppm): δ 7.77−7.69 (m, 4H), 7.60−7.46 (m, 6H), 2.73−2.54
(m, 4H). 13C{1H} NMR (63 MHz, CDCl3, ppm): δ 132.6 (d, J = 2.7
Hz, CH or CH3), 131.1 (d, J = 101.3 Hz, C), 130.8 (d, J = 9.6 Hz, CH
or CH3), 129.1 (d, J = 12.0 Hz, CH or CH3), 118.6 (d, J = 18.3 Hz,
C), 26.3 (d, J = 70.1 Hz, CH2), 10.5 (d, J = 0.8 Hz, CH2). 31P{1H}
NMR (101.3 MHz, CDCl3, ppm): δ 28.27. These NMR data matched
previously reported data.39
2-(Diphenylphosphinyl)ethyl Phenyl Sulfone (7c). White solid (79
mg, 84%) obtained from diphenylphosphine oxide (6a, 50.5 mg) and
phenyl vinyl sulfone (50 mg) using ICy·CO2 (3.4 mg). 1H NMR (250
MHz, CDCl3, ppm): δ 7.87−7.84 (m, 2H), 7.73−7.62 (m, 5H), 7.57−
7.44 (m, 8H), 3.33−3.24 (m, 2H), 2.74−2.63 (m, 2H). 13C{1H} NMR
(63 MHz, CDCl3, ppm): δ 138.4 (s, C), 134.2 (s, CH or CH3), 132.5
(d, J = 2.8 Hz, CH or CH3), 131.4 (d, J = 101.9 Hz, C), 130.8 (d, J =
9.6 Hz, CH or CH3), 129.6 (s, CH or CH3), 129.1 (d, J = 12.0 Hz, CH
or CH3), 128.2 (s, CH or CH3), 49.5 (d, J = 2.0 Hz, CH2), 23.3 (d, J =
68.4 Hz, CH2). 31P{1H} NMR (101.3 MHz, CDCl3, ppm): δ 28.05.
HRMS (ESI+): m/z [M + Li]+ calcd for C20H19O3PSLi+ 377.0947,
obsd 377.0944.
ASSOCIATED CONTENT
■
S
* Supporting Information
1
Figures giving H and 13C NMR spectra for all compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.
4-(Diphenylphosphinyl)butan-2-one (7e). Colorless oil (55 mg,
81%) obtained from diphenylphosphine oxide (6a, 50.5 mg) and
F
dx.doi.org/10.1021/jo500108a | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Note
(30) Naik, P. U.; Petitjean, L.; Refes, K.; Picquet, M.; Plasseraud, L.
Adv. Synth. Catal. 2009, 351, 1753.
(31) Pinaud, J.; Vignolle, J.; Gnanou, Y.; Taton, D. Macromolecules
AUTHOR INFORMATION
Corresponding Authors
*E-mail for L.D.: l.delaude@ulg.ac.be.
*E-mail for J.R.: jean.rodriguez@univ-amu.fr.
*E-mail for Y.C.: yoann.coquerel@univ-amu.fr.
■
2011, 44, 1900.
̀
(32) Fevre, M.; Coupillaud, P.; Miqueu, K.; Sotiropoulos, J.-M.;
Vignolle, J.; Taton, D. J. Org. Chem. 2012, 77, 10135.
(33) Duong, H. A.; Cross, M. J.; Louie, J. Org. Lett. 2004, 6, 4679.
(34) Bantu, B.; Pawar, G. M.; Wurst, K.; Decker, U.; Schmidt, A. M.;
Buchmeiser, M. R. Eur. J. Inorg. Chem. 2009, 1970.
(35) Naik, P. U.; Refes, K.; Sadaka, F.; Brachais, C.-H.; Boni, G.;
Couvercelle, J.-P.; Picquet, M.; Plasseraud, L. Polym. Chem. 2012, 3,
1475.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Financial support from the European CMST COST Action
CM0905 on organocatalysis, the Universite
■
́
̀
de Liege, Aix-
̀
(36) Fevre, M.; Pinaud, J.; Leteneur, A.; Gnanou, Y.; Vignolle, J.;
Taton, D.; Miqueu, K.; Sotiropoulos, J.-M. J. Am. Chem. Soc. 2012,
134, 6776.
(37) Ortega, N.; Richter, C.; Glorius, F. Org. Lett. 2013, 15, 1776.
(38) Brandau, S.; Maerten, E.; Jørgensen, K. A. J. Am. Chem. Soc.
2006, 128, 14986.
Marseille Universite,
Scientifique (CNRS) is gratefully acknowledged.
́
and the Centre National de la Recherche
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