Triazolium salts as appropriate catalytic scaffolds for 1,4-additions to α,β-unsaturated carbonyls

Article abstract of DOI:10.1002/ejoc.201301220

1,2,3-Triazole derivatives containing a rigid dihydroanthracenyl skeleton are suitable precursors for both organometallic and organo-based catalysts. A Rh-carbene complex and the triazolium salt efficiently catalyzed the 1,4-additions of C- and heterodonor reagents to α,β-unsaturated carbonyl substrates, respectively. Copyright

Full text of DOI:10.1002/ejoc.201301220

FULL PAPER
DOI: 10.1002/ejoc.201301220
Triazolium Salts as Appropriate Catalytic Scaffolds for 1,4-Additions to
α,β-Unsaturated Carbonyls
Ielyzaveta Bratko,[a] Gregorio Guisado-Barrios,[b] Isabelle Favier,[a] Sonia Mallet-Ladeira,[c]
Emmanuelle Teuma,[a] Eduardo Peris,*[b] and Montserrat Gómez*[a]
Keywords: Rhodium / Organocatalysis / Mesoionic carbene / Nitrogen heterocycles / Michael addition
1,2,3-Triazole derivatives containing
anthracenyl skeleton are suitable precursors for both organo-
metallic and organo-based catalysts. A Rh–carbene complex
a
rigid dihydro-
and the triazolium salt efficiently catalyzed the 1,4-additions
of C- and heterodonor reagents to α,β-unsaturated carbonyl
substrates, respectively.
are attributed to the high π-acceptor ability of the ligand.[7a]
More recently, Nolan and co-workers have published an ef-
ficient RhI catalyst that combines the presence of both a
strongly electron-donating N-heterocyclic carbene (NHC)
and a poorly electron-donating bidentate cyclooctadiene
(cod) ligand.[9]
Introduction
The 1,4-additions of nucleophiles to α,β-unsaturated
compounds represent the foremost organic transformation
for the production of fine chemicals.[1] Metal-catalyzed
processes, in particular conjugate additions to enones,
constitute a convenient tool for the formation of C–C
bonds.[2a–2d] Although copper is the most widely used metal
for this type of transformation,[3] it exhibits, together with
Grignard or organozinc reagents, some important experi-
mental drawbacks (low temperature thresholds, high water-
sensitivity). Rhodium catalysts have recently been shown to
have some advantages, especially as they allow the use of
mild organometallic reagents (e.g., organoboron com-
pounds) and often afford high chemoselectivities. They also
permit the use of aryl nucleophiles, which are ineffective
when Cu-based catalysts are involved.[4] Since the pioneer-
ing work of Miyaura proved the efficiency of Rh–phosphine
catalytic systems for the conjugate additions of boronic ac-
ids to enones,[5] many contributions in which the metal is
accompanied by different types of spectator ligands, such
as dienes,[6] diphosphines[7] or phosphoramidites, have been
reported.[8] Noticeable examples have been reported in
which weak σ-donating ligands such as the diphosphine
MeO-F12-BIPHEP lead to remarkably high activities, which
This complex leads to the stabilization of Rh hydroxo
species, which had previously been postulated as intermedi-
ates in transmetallations with organoboronic acids.[10]
Complementarily, NHC-based organocatalysis consti-
tutes a convenient strategy for the formation of C–hetero-
atom bonds from α,β-unsaturated carbonyl derivatives, be-
cause it overcomes any possible poisoning of the metal spe-
cies by the nucleophile (such as thiols or amines).[2e,2f] In
this regard, acid-mediated hetero-Michael reactions can ac-
tivate the Michael acceptor to give conjugate additions un-
der mild conditions, in contrast to the harsher conditions
required for base activation of nucleophiles.[11] Among the
Lewis acids reported in the literature,[11a] functionalized
imidazolium salts have specifically attracted our attention
because they permit both metal-free and solvent-free
conditions.[12]
On the basis of our experience in the functionalization
of ligands containing the rigid 9,10-dihydroanthracenyl
skeleton[13a–13c] and in the field of NHC-based metal-medi-
ated catalysis,[14] we decided to design an original triazole
(A, Scheme 1), which could serve both as an organocatalyst
precursor and as a 1,2,3-triazolylidene organometallic pre-
cursor for the promotion of 1,4-additions of α,β-unsatu-
rated carbonyl compounds. We believe that the combination
of a 1,2,3-triazolylidene and 9,10-dihydroanthracenyl may
benefit from the unique properties associated with both
fragments. Additionally, as we have previously reported,[13c]
the presence of the aromatic rings associated with the dihy-
droanthracenyl skeleton should allow the π coordination of
a metal fragment to potentially facilitate the formation of
heterometallic complexes, which may offer interesting coop-
[a] Université de Toulouse, UPS, LHFA, and CNRS, LHFA UMR
5069,
118 route de Narbonne, 31062 Toulouse Cedex 9, France
E-mail: gomez@chimie.ups-tlse.fr
http://hfa.ups-tlse.fr/SYMAC/index_symac.htm
[b] Departamento de Química Inorgánica y Orgánica, Universitat
Jaume I,
Avenida Vicente Sos Baynat s/n, 12071 Castellón, Spain
E-mail: eperis@qio.uji.es
http://qomcat.uji.es
[c] Université de Toulouse, UPS, Institut de Chimie de Toulouse
FR2599,
118 route de Narbonne, 31062 Toulouse Cedex 9, France
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201301220.
2160
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2014, 2160–2167

Triazolium Salts as Catalytic Scaffolds for 1,4-Additions
erative catalysis effects.[13d] In this preliminary work, we ure 1) and triazole A (Figure S2) afforded suitable single
have established the basis for the convenient preparation crystals for the determination of their X-ray molecular
and the coordination abilities of a new 9,10-dihydro- structures.
anthracenyl-based triazolylidene. The catalytic properties of
both the uncoordinated triazole and the rhodium complex
are also explored.
Figure 1. Molecular view of RhB (ellipsoids represent 50% prob-
ability). Hydrogen atoms and an acetonitrile molecule are omitted
for clarity. Selected bond lengths [Å] and angles [°]: Rh(1)–C(1)
2.017(3), Rh(1)–Cl(2) 2.379(8), Rh(1)–C(5) 2.100(3), Rh(1)–C(6)
2.114(3), Rh(1)–C(7) 2.188(3), Rh(1)–C(8) 2.177(3), C(1)–Rh(1)–
Cl(2) 89.34 (8).
The structure of RhB consists of a 1,2,3-triazolylidene
ligand coordinated to a RhI fragment (Figure 1). A 1,5-cy-
clooctadiene ligand and a chloride ion complete the coordi-
nation sphere about the metal centre. The Rh–C(carbene)
distance is 2.017 Å. The plane of the azole ring is quasiper-
pendicular with respect to the coordination plane of the
molecule. All other distances and angles are unexceptional.
As the rotation around the C2–C3 bond in RhB is steri-
cally hindered (Figure 1), two different conformers may be
expected (Figure S3). The calculated relative energy of both
isomers (ΔE = +3.2 kcal/mol) may justify the formation of
Scheme 1. Synthesis of the triazole A, triazolium salts B and C and
Rh carbene complex RhB, [RhCl(cod)(NHC-B)].
Results and Discussion
As shown in Scheme 1, the 1,2,3-triazole A leads to the only one species both in solution (NMR analysis) and in
preparation of the 1,2,3-triazolylidene rhodium(I) complex the solid state. The conformer observed by XRD analysis
RhB and the triazolium salt C, both of which have the po- corresponds to the most-stable calculated isomer.
tential to behave as catalyst precursors for conjugate ad-
ditions.
Complex RhB was tested in the catalytic conjugate ad-
ditions of aryl boronic acids a–d to enones 1–4 (Scheme 2
The new compounds A–C were prepared by previously and Table 1). The addition of phenylboronic acid (a) to
reported methodologies from the Diels–Alder anhydride chalcone (1) was used as a benchmark transformation. Af-
adduct by condensation with the corresponding primary ter optimizing the reaction conditions, we observed that the
amine followed by a copper-mediated cycloaddition of the use of toluene and KOH afforded the best catalytic out-
[13c,15]
alkyne with BnN3
to yield triazole A in good yield comes (Table S1). The results shown in Table 1 reflect that
(76%). The quaternization of A with MeI or p-toluene- the electronic nature of the aryl moiety has a significant
sulfonic acid (TsOH) afforded the triazolium salts B[16] and influence on the reactivity. With (4-OMe-C6H4)B(OH)2, the
C,[12] respectively (yields Ͼ 84%). Compound B may be reactions were faster (Table 1, Entries 2, 5, 8 and 11). In
used as a precursor of a mesoionic carbene (MIC)[16] and this regard, enones 1 and 3 achieved isolated yields on the
leads to the formation of complex RhB by transmetallation desired products (1b and 3b, respectively) of up to 98%
of the corresponding in situ prepared silver–MIC com- (Table 1, Entries 2 and 8). Longer reaction times (24 h) es-
pound.[16e] Compounds A–C and the organometallic com- sentially produced the same trend. It is important to note
plex RhB were fully characterized by the conventional tech- the high activity exhibited for (R)-carvone with 4-meth-
niques (see Supporting Information for synthetic protocols, oxyphenyl boronic acid (82% isolated yield of 4b; Table 1,
characterization data and Figure S1). Complex RhB (Fig- Entry 11), in contrast to the negligible activity observed
Eur. J. Org. Chem. 2014, 2160–2167
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2161

E. Peris, M. Gómez, et al.
FULL PAPER
when phenyl boronic acid was used (Table 1, Entry 10). Table 1. 1,4-additions of aryl boronic acids a–e to enones 1–4 cata-
lyzed by RhB.[a]
Compound 4b was obtained as a mixture of anti and syn
[b]
diastereomers in a ratio of 12:1 (Table 1, Entry 11). The bo-
ronic acid c [(4-CF3-C6H4)B(OH)2] afforded low-to-negligi-
ble conversions (Ͻ42%: Table 1, Entries 3, 6, 9 and 12).
These results demonstrate that the conjugate addition cata-
lyzed by RhB is sensitive to the electronic nature of the
arene nucleophile, in contrast to the results previously re-
ported for other RhI complexes containing dienes.[17,18]
Also, the reaction does not need the addition of extra 1,5-
cyclooctadiene and occurs at a lower temperature than that
shown in a recent example for a related NHC–Rh(cod)
complex.[19] Complex RhB was also efficient when the steri-
cally demanding boronic acid (2-Me-C6H4)B(OH)2 (d) was
Entry
Enone[b] ArB(OH)2
Conversion [%][c]
84 (90) [70]
1
2
3
4
5
6
7
8
1
1
1
2
2
2
3
3
3
4
4
a, Ar = Ph
b, Ar = 4-OMe-C6H4 100 [98][d]
c, Ar = 4-CF3-C6H4 37 (42)
a, Ar = Ph
28 (95) [89]
b, Ar = 4-OMe-C6H4 76 (85) [85]
c, Ar = 4-CF3-C6H4 35 (35)
a, Ar = Ph
43 (51)
b, Ar = 4-OMe-C6H4 100 [98]
c, Ar = 4-CF3-C6H4 38 (38)
9
10
11
a, Ar = Ph
6 (9)
b, Ar = 4-OMe-C6H4 87 (87) [82] dr = 12:1
(anti/syn)[e]
12
4
2
3
c, Ar = 4-CF3-C6H4 0 (0)
d, Ar = 2-Me-C6H4
d, Ar = 2-Me-C6H4
used for the conjugate addition to cyclic enones 2 and 3 13
(Table 1, Entries 12–13) and afforded 2d in high yield (87%;
88 (97) [87]
28 (33)
14
Table 1, Entry 13). Unfortunately, RhB was inactive for the
addition of the boronic acid d to enones 1 and 4.
[a] Reaction conditions: 0.5 mmol of conjugated enone, 0.6 mmol
of aryl boronic acid, 0.375 mmol of KOH, 0.005 mmol of RhB,
0.5 mL of toluene, 40 °C, 5 h. See Table S2 for blank tests. [b] See
Scheme 2. [c] Average of two experiments. Determined by 1H NMR
spectroscopy with 2,4,6-trimethylphenol as internal standard; in
parenthesis, data at 24 h; in square brackets, isolated yields. [d] 2 h
reaction. [e] Diastereomeric ratio determined by 1H NMR spec-
troscopy; see Figures S4–S6.
Scheme 2. Rh-catalyzed 1,4-additions of aryl boronic acids to en-
ones.
Scheme 3. Rh-catalyzed tandem addition of aryl boronic acids to
cinnamaldehyde. In brackets, data obtained in methanol.
It is important to point out that the reactions with RhB
did not afford any byproducts, which demonstrates the ex-
To create C–heteroatom bonds, we performed the ad-
cellent chemoselectivity of the reactions.[20] This behaviour dition of ethyl carbamate to 2-cyclohexenone, but the Rh-
is in contrast to that observed when [RhCl(cod)]2 is used based catalyst was completely inactive. We then decided to
(Table S3). For enones 1–3, [RhCl(cod)]2 was more active study the organocatalytic ability of the triazolium salt C
than RhB in terms of product yields, but the deboronation (Scheme 1) in Michael additions with the α,β-unsaturated
product (anisole) was also obtained in 15% yield. For (R)- ketones 1–4 as Michael acceptors and the heterodonor rea-
carvone, [RhCl(cod)]2 was much less active than RhB (28% gents e–g as nucleophiles (Scheme 4 and Table 2).[22] The
conversion after 24 h) and yielded 44% of anisole.
triazolium salt C was obtained in high yield by the reaction
To evaluate the regioselectivity (1,4- vs. 1,2-addition) and of A with p-toluenesulfonic acid at 60 °C (see Supporting
the chemoselectivity (1,4-addition followed by 1,2-addition) Information for synthetic protocol and characterization
of RhB, we decided to study the addition of (4-OMe-C6H4)- data).[12,23] We chose 2-cyclohexenone (2) and ethyl carb-
B(OH)2 to cinnamaldehyde (Scheme 3). After 5 h of reac- amate (e) as model substrates for the Michael addition cata-
tion, full conversion was achieved, mainly leading to the lyzed by C. At low catalyst loadings, we observed high ac-
formation of the double arylation product 6 (61%). Both tivities after 24 h of reaction (Table 2, Entries 1–3), in con-
the 1,2- and the 1,4-addition products (7 and 8, respec- trast to the lower reported reactivity for imidazolium deriv-
tively) were also detected (less than 8%).[21] With methanol atives.[12] At shorter reaction times (5 h), the best conditions
instead of toluene, RhB exhibited the same activity, but the were obtained with a catalyst load of 2 mol-% (83% conver-
process was less selective and favoured the 1,4-addition sion, see Table S4). No relevant differences were observed
product 8, in agreement with the reported data.[17]
with the pure preformed catalyst C instead of the in situ
2162
www.eurjoc.org
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2014, 2160–2167

Triazolium Salts as Catalytic Scaffolds for 1,4-Additions
product generated by the reaction of an equimolecular mix-
ture of A and TsOH (Table 2, Entries 1 and 2). In the ab-
sence of A, p-toluenesulfonic acid was certainly less active
(Table 2, Entry 4).
Figure 2. Triazoles D–F and the corresponding triazolium deriva-
tives G–I.
Scheme 4. Hetero-Michael additions of α,β-unsaturated ketones
with N-, O- and S-containing nucleophiles catalyzed by triazolium
salt C.
The conversions provided by triazole derivatives contain-
ing phenyl (E and H) and cyclohexyl (F and I) substituents
are significantly lower than those provided by the 9,10-dihy-
droanthracenyl-containing azoles A and C (Table 2, Entries
12, 15, 13 and 16 vs. 1–3) and afforded almost identical
results to those for the use of only TsOH (Table 2, Entry 4);
thus, the influence of the triazolium salts H and I in the
catalytic activity may be negligible. However, triazoles D
and G, derived from the succinic anhydride, gave almost
identical results to those for A and C; therefore, the succinic
anhydride moiety induces a positive effect on the catalytic
activity (Table 2, Entries 1 vs. 14 and 2 vs. 11). Given the
easier accessibility of A and C from the synthetic point of
view, we consider the 9,10-dihydroanthracenyl-containing
azoles as more convenient organocatalysts for the hetero-
Michael additions studied.
Table 2. Hetero-Michael additions of N-, O- and S-containing nu-
cleophiles to α,β-unsaturated ketones catalyzed by the triazolium
salt C.[a]
Entry Catalyst
Catalyst Ketone Nucleophile Conversion
load [%]
[%][b]
1
2
C
2
2
1
2
2
2
2
1
3
4
2
2
2
2
2
2
2
2
2
e
e
e
e
e
e
e
f
g
g
e
e
e
e
e
e
90 (80)
91 (80)
90 (80)
62
0
50
18
31
98 (73)
11
95 (85)
60
A + TsOH
A + TsOH
TsOH
3[c]
4
2
5
6
7
8
A + TsOH
A + TsOH
A + TsOH
A + TsOH
A + TsOH
A + TsOH
D + TsOH
E + TsOH
F + TsOH
G
10
10
10
10
10
2
2
2
2
2
9[d]
10[d]
11
12
13
14
15
16
85
80 (75)
55
Conclusions
H
I
2
2
55
We have obtained a 1,2,3-triazole (A) that can serve both
as an organocatalyst precursor (to give the triazolium salt
C) or a 1,2,3-triazolylidene, an NHC-type ligand precursor
for the preparation of a metal-based catalyst (the organo-
metallic complex RhB), for the promotion of 1,4-additions
to α,β-unsaturated carbonyl compounds. The rhodium cat-
alyst exhibits excellent chemoselectivity for C–C bond for-
mation, especially when compared to [RhCl(cod)]2, under
[a] Conditions: 0.30 mmol of enone, 0.36 mmol of nucleophile,
0.006–0.03 mmol of the corresponding triazole, 0.006–0.03 mmol
of TsOH, 0.25 mL of CH2Cl2, 25 °C, 24 h. [b] Average of two ex-
periments; determined by 1H NMR spectroscopy with 2,4,6-tri-
methylphenol as internal standard; in brackets, isolated yields. [c]
Conditions: 1.0 mmol of enone, 1.2 mmol of nucleophile,
0.01 mmol of A, 0.01 mmol of TsOH, 0.25 mL of CH2Cl2, 25 °C,
24 h. [d] Traces of p-tolyl disulfide were observed.
Catalyst C was less efficient for Michael additions when milder reaction conditions than those for previously re-
enones 1, 3 and 4 were involved (Table 2, Entries 5–7) and ported Rh-NHC based catalysts in the same reactions.[9,19]
yielded only 50% of 3e after 24 h of reaction with 10 mol- The triazolium salt C was tested in the hetero-Michael ad-
% of catalyst.
dition of α,β-unsaturated ketones at low catalyst loads and
To assess the effect of the 9,10-dihydroanthracenyl back- is more effective than other imidazolium-based catalysts.[12]
bone on the activity of the triazolium salt C, we decided to We believe that this dual use of A, as organocatalyst precur-
evaluate the catalytic activity of the related benzyl-substi- sor and as a ligand precursor for an organometallic-based
tuted triazolium derivatives, G, H and I, derived from the catalyst, illustrates the great potential of MIC–NHCs in the
triazoles D,[24] E[25] and F,[26] respectively (Figure 2). These field of homogeneous catalysis and widens the gap between
compounds can be considered similar to the triazole A and traditional spectator ligands and ligands such as NHCs,
the triazolium C, but as they do not possess the 9,10-dihy- which are capable of promoting both effective organocata-
droanthracenyl group, they are good systems for compari- lysis and metal-promoted catalysis. 9,10-Dihydroanthracen-
son purposes. The triazole D was obtained in a very low yl is not necessary to promote the catalytic activity of the
yield (less than 15%) under the smooth conditions used to triazolium salts (the catalytic results provided by D and G
synthesize A and E (Scheme 1); we then tried harsher reac- are similar to those shown by A and C), and the easier
tion conditions (100 °C, 2 h in the presence of Cu2O as cat- synthetic access to A and C makes them better catalyst
alyst; see Experimental Section), which led to the expected choices. Also, the presence of the 9,10-dihydroanthracenyl
product in quantitative yield.
fragment attached to the NHC moiety may allow the for-
Eur. J. Org. Chem. 2014, 2160–2167
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2163

E. Peris, M. Gómez, et al.
FULL PAPER
mation of heterodimetallic complexes,[13c] the properties of
which may provide interesting cooperative catalytic effects
and, therefore, may widen the scope of its applicability.
16), 33.9 (C-19) ppm. IR (KBr): ν = 3069 (=C–H), 2956 (C–H),
˜
1701 (C=O), 1466 (C=C) cm–1. HRMS (ES+, acetonitrile): calcd.
for C28H22N4O2Na [M + Na]+ 469.1640; found 469.1649.
Compound B: To a solution of triazole A (287 mg, 0.644 mmol) in
MeCN (5 mL) was added CH3I (220 μL, 3.54 mmol), and the mix-
ture was heated at 60 °C for 72 h. All volatiles were then removed
in vacuo. The solid residue was washed with hexane and dried to
afford the triazolium salt B; yield 319 mg (84%). 1H NMR
(300 MHz, 298 K, CD3CN): δ = 7.96 (s, 1 H, H-21), 7.50 (m, 5 H,
Experimental Section
General Methods: Manipulations of compounds sensitive to air or
moisture were performed under argon by using standard Schlenk
techniques. Solvents were purified prior to use. Chemicals were
used as purchased (from Acros Organics or Sigma Aldrich). NMR
spectra were recorded with a Bruker Avance 300 spectrometer or a
Varian Innova spectrometer operating at 300 or 500 MHz (1H
NMR) and 75 or 125 MHz (13C NMR), respectively, with CDCl3
as solvent at room temperature unless otherwise stated. IR spectra
were measured with a Varian 640-IR FTIR spectrometer. Mass
spectra were recorded with a Waters GCT 1er (chemical ionization)
or UPLC Xevo G2 Q Tof instrument. Electrospray mass spectra
(ESI-MS) were recorded with a Micromass Quatro LC instrument,
and nitrogen was employed as the drying and nebulizing gas. Theo-
retical studies were performed with the following software: SPART-
AN’06 for Windows and Linux (Wavefunction, Inc., 18401 Von
Karmaan Avenue, suite 370. Irvine, CA 92612, USA).
Harom), 7.40–7.43 (m, 2 H, Harom), 7.17–7.20 (m, 2 H, Harom), 7.08–
7.11 (m, 2 H, Harom), 6.77–6.80 (m, 2 H, Harom), 5.70 (s, 2 H, H-
22), 4.75 (m, 2 H, 9-H, 10-H), 4.43 (s, 2 H, 19-H), 4.00 (s, 3 H, 23-
H), 3.33 (m, 2 H, 15-H, 16-H) ppm. 13C NMR (75 MHz, 298 K,
CD3CN): δ = 176.9 (C-17, C-18), 142.2, 140.3 (C-11–C-14), 138.5
(C-20), 132.9 (CPh), 131.2 (CHPh), 130.8 (C-21), 130.3, 130.1
(CHPh), 127.6, 127.2, 125.5, 125.3 (Carom), 58.0 (C-22), 47.5 (C-9,
C-10), 46.0 (C-15, C-16), 39.4 (C-23), 30.3 (C-19) ppm. IR (KBr):
ν = 3036 (=C–H), 2936 (C–H), 1706 (C=O), 1467 (C=C) cm–1.
˜
HRMS (ES+, acetonitrile): calcd. for C29H25N4O2 [M – I]+
461.1978; found 461.1982.
Compound C: To triazole A (30 mg, 0.067 mmol) was added
TsOH·H2O (12.8 mg, 0.067 mmol), and the mixture was heated at
60 °C for 72 h. The solid residue afforded the triazolium salt C;
yield 40.7 mg (98%). 1H NMR (300 MHz, 298 K, CDCl3): δ = 8.00
(br. s, 1 H, NH), 7.72 (d, J = 8.2 Hz, 2 H, Harom OTs), 7.42–7.44
(m, 3 H, Harom), 7.30–7.34 (m, 4 H, Harom), 7.10–7.16 (m, 6 H,
Harom), 6.93 (s, 1 H, 21-H), 6.77–6.81 (m, 2 H, Harom), 5.53 (s, 2
H, 22-H), 4.72 (s, 2 H, 9-H, 10-H), 4.57 (s, 2 H, 19-H), 3.28 (m, 2
H, 15-H, 16-H), 2.35 (s, 3 H, MeOTs) ppm. 13C NMR (75 MHz,
298 K, CDCl3): δ = 175.9 (C-17, C-18), 141.5, 141.0, 139.1, 132.0
(Carom), 129.7, 129.4 (Carom), 129.0 (CHOTs), 128.5, 126.8, 126.5
(Carom), 126.2 (CHOTs), 124.9 (Carom and C-21), 124.3 (Carom),
56.3 (C-22), 46.9 (C-15, C-16), 45.2 (C-9, C-10), 31.6 (C-19), 21.4
Compound II: The anhydride I (500 mg, 1.81 mmol) was suspended
in MeOH (15 mL), and the mixture was cooled to 0 °C. A solution
of N-propargylamine (174 μL, 2.72 mmol) in MeOH (5 mL) was
added dropwise (5 min), and the resulting solution was stirred for
5 min at 0 °C, 30 min at room temperature and finally heated to
reflux for 72 h. After the mixture cooled to room temperature, the
solvent was removed under reduced pressure, and the residue was
dissolved in DCM (dichloromethane, 50 mL) and washed with
water (3ϫ50 mL). The organic layer was dried with MgSO4 and
filtered. Removal of the solvent under reduced pressure furnished
II as a yellow solid; yield 532 mg (94%). 1H NMR (300 MHz,
298 K, CDCl3): δ = 7.36–7.39 (m, 2 H, Harom), 7.25–7.28 (m, 2 H,
Harom), 7.16–7.19 (m, 2 H, Harom), 7.09–7.12 (m, 2 H, Harom), 4.80
(m, 2 H, 9-H, 10-H), 3.80 (d, J = 2.5 Hz, 2 H, 19-H), 3.24 (m, 2
H, 15-H, 16-H), 1.88 (t, J = 2.5 Hz, 1 H, 21-H) ppm. 13C NMR
(75 MHz, 298 K, CDCl3): δ = 175.8 (C-17, C-18), 141.5, 138.6 (C),
127.3, 127.0, 125.1, 124.4 (Carom), 76.0 (C-20), 70.9 (C-21), 47.2 (C-
(MeOTs) ppm. IR (KBr): ν = 3453 (N–H), 3068, 3020 (=C–H),
˜
2956 (C–H), 1702 (C=O), 1466, 1425 (C=C), 1154 (S=O) cm–1.
HRMS (ES+, methanol): calcd. for C28H23N4O2 [M – OTs]+
447.1821 (positive); found 447.1814; calcd. for C7H7SO3 [OTs]–
171.0116 (negative); found 171.0127.
N-Allylsuccinimide:[28] Succinic anhydride (800 mg, 8 mmol) and N-
propargylamine (0.8 mL, 14 mmol) were dissolved in toluene
(15 mL) in the presence of molecular sieves. The mixture was
heated to reflux for 48 h. After the reaction mixture cooled to room
temperature, the solvent was removed under reduced pressure to
give a yellow solid; yield 578 mg (53%). 1H NMR (300 MHz,
298 K, CDCl3): δ = 4.22 (d, J = 2.5 Hz, 2 H), 2.73 (s, 4 H), 2.18
(t, J = 2.5 Hz, 1 H) ppm. 13C NMR (75 MHz, 298 K, CDCl3): δ =
175.9 (C=O), 71.4 (CH), 28.2 (CH2), 27.7 (CH2) ppm.
Compound D: Benzyl azide[27] (160 mg, 1 mmol) and N-allylsuc-
cinimide (137 mg, 1 mmol) were added to a Cu2O/glycerol catalytic
solution (2.5 mL, 0.01 m). The mixture was stirred for 2 h at 100 °C.
After the mixture cooled to room temperature, the product was
extracted with dichloromethane. The combined organic layers were
filtered through Celite and concentrated in vacuo; yield 283 mg
(Ͼ99%). 1H NMR (300 MHz, 298 K, CDCl3): δ = 7.50 (s, 1 H,
Halkene), 7.36–7.38 (m, 2 H, Ph), 7.28 (m, 2 H, Ph), 5.48 (s, 2 H,
CH2N), 4.77 (s, 2 H, CH2–Ph), 2.72 (s, 4 H) ppm. 13C NMR
(75 MHz, 298 K, CDCl3): δ = 176.6 (C=O), 134.4 (CPh), 129.1,
128.8, 128.2 (CHPh), 122.9 (CH=C), 54.2 (CH2N), 33.7 (CH2Ph),
28.2 (CH2) ppm.
9, C-10), 45.7 (C-15, C-16), 27.4 (C-19) ppm. IR (KBr): ν = 3265
˜
(ϵC–H), 3074 (=C–H), 2968 (C–H), 2128 (CϵC), 1706 (C=O),
1467 (C=C) cm–1. ESI (MeOH): m/z = 314.3 [M + H]+, 336.2 [M
+ Na]+, 352.2 [M + K]+. HRMS (CI, CH2Cl2): calcd. for
C21H16NO2 [M + H]+ 314.1181; found 314.1173.
Compound A: To a stirred solution of benzyl azide[27] (332 mg,
2.50 mmol) in THF (15 mL), the intermediate II (261 mg,
0.833 mmol) was added at 0 °C followed by the addition of
CuSO4·5H2O (21 mg, 0.083 mmol), sodium ascorbate (82.5 mg,
0.417 mmol) and water (5 mL). The mixture was stirred for 5 min
at 0 °C and then overnight at room temperature. The reaction was
quenched by the addition of excess conc. aq. NH4OH, stirred for
3 h and then extracted with DCM. The combined organic layers
were dried with MgSO4 and concentrated in vacuo; yield 300 mg
(81%). Single crystals were obtained from a dichloromethane/di-
isopropyl ether (1:4) solution. 1H NMR (300 MHz, 298 K, CDCl3):
δ = 7.34–7.40 (m, 5 H, Harom and 1-H of Ph), 7.19–7.22 (m, 2 H,
Ph), 7.14–7.17 (m, 4 H, Harom), 6.83–6.86 (m, 2 H, Ph), 6.56 (s, 1
H, 21-H), 5.40 (s, 2 H, 22-H), 4.76 (m, 2 H, 9-H, 10-H), 4.42 (s, 2
H, 19-H), 3.23 (m, 2 H, 15-H, 16-H) ppm. 13C NMR (75 MHz,
298 K, CDCl3): δ = 176.0 (C-17, C-18), 141.4, 138.8 (C-20), 134.6
Compounds G, H and I: To triazole D[24] (108 mg, 0.42 mol), E[25]
(CPh), 129.0, 128.7, 127.8 (CHPh), 126.8 (Carom and C-21), 126.6, (100 mg, 0.42 mol) or F[26] was added TsOH·H2O (80 mg,
124.9, 124.2 (Carom), 53.9 (C-22), 46.8 (C-9, C-10), 45.3 (C-15, C- 0.42 mol), and the mixture was heated at 60 °C for 72 h. The solid
2164
www.eurjoc.org
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2014, 2160–2167

Triazolium Salts as Catalytic Scaffolds for 1,4-Additions
residue was washed with diethyl ether to yield the triazolium salts
cusing multilayer optics and Mo-Kα radiation (λ = 0.71073 Å); φ
and ω scans were used. The data were integrated with SAINT, and
G, H and I. Yields: 136 mg (76%) for G, 131.8 mg (76%) for H,
1
142 mg (82%) for I. G: H NMR (300 MHz, 298 K, CDCl3): δ = a semi-empirical absorption correction with SADABS was ap-
8.16 (br., 1 H, CH=), 7.71 (d, J = 7.9 Hz, 2 H, anion), 7.37–7.28 plied.[29] The structure was solved by direct methods by using
(m, 5 H, Harom), 7.16 (d, J = 7.9 Hz, 2 H, anion), 5.59 (s, 2 H),
4.88 (s, 2 H), 2.73 (s, 3 H), 2.35 (s, 2 H) ppm. 13C NMR (75 MHz,
298 K, CDCl3): δ = 177.1 (C=O), 141.3, 140.1, 130.4 (Carom), 129.5,
SHELXS-97 and refined by using the least-squares method on F2
with SHELXL-97.[30] All non-H atoms were treated anisotropically,
and the H atoms were refined by using a riding model. Selected
129.3, 129.1, 128.9 (Carom), 126.1 (CH=), 56.3 (CH2), 32.2 (CH2), crystal data: C28H22N4O2, M = 446.50, monoclinic, space group
28.4 (CH2), 21.4 (CH3) ppm. HRMS (ES+, MeOH): calcd. for P21/c, a = 7.7787(6) Å, b = 22.799(2) Å, c = 12.4422(12) Å, α =
C14H15N4O2 [M – OTs]+ 271.1190; found 271.1202. HRMS (ES–, 90°, β = 101.056(5)°, γ = 90°, V = 2165.6(3) Å3, Z = 4, crystal size
methanol): calcd. for C7H7O3S [OTs]– 171.0116; found 171.0119.
For H: H NMR (300 MHz, 298 K, CDCl3): δ = 13.9 (br. s, 1 H, dent, Rint = 0.0918), 307 parameters, R1 [IϾ2σ(I)] = 0.0468, wR2
0.40ϫ0.16ϫ0.02 mm, 25364 reflections collected (3098 indepen-
1
NH), 8.62 (br. s, 1 H, H tr), 7.79 (m, 4 H, H Ts) 7.32 (m, 8 H,
H
(all data) = 0.1364, largest diff. peak and hole: 0.269 and
arom), 7.14 (br., 2 H, Harom), 5.60 (s, 2 H, 1-H), 2.33 (s, 3 H, H –0.270 eÅ–3.
Ts) ppm. 13C NMR (75 MHz, 298 K, CDCl3): δ = 144.0, 141.3,
140.9, 136.0, 132.5, 130.9, 129.6, 129.4, 129.1, 129.0, 127.0, 126.3,
124.4, 123.9 (C-7), 56.7 (C-1), 21.5 (C Ts) ppm. HRMS: (ES+,
methanol): calcd. for C15H14N3 [M + H]+ 236.1188; found
236.1191. HRMS (ES–, methanol): calcd. for C7H7O3S [OTs]–
Crystallographic Data for RhB: Single crystals of C39H39ClN5O2Rh
were mounted on a MicroMount® polymer tip (MiteGen) in a ran-
dom orientation. Data collection was performed with an Agilent
Technologies SuperNova (Dual, Cu at zero, Atlas) diffractometer.
The crystal was kept at 150.05(10) K during data collection. By
using Olex2, the structure was solved with the ShelXS[31] structure
solution program by using direct methods and refined with the
ShelXL[30] refinement package using least-squares minimization.
All non-H atoms were treated anisotropically, and the H atoms
were refined by using a riding model. Selected crystal data:
C39H39ClN5O2Rh, M = 748.11, monoclinic, space group P21/c, a
= 9.4175(4) Å, b = 20.5109(10) Å, c = 17.9854(11) Å, α = 90°, β =
97.070(5)°, γ = 90°, V = 3447.6(3) Å3, Z = 4, crystal size
0.3191ϫ0.0996ϫ0.0607 mm, 39235 reflections collected (8708
unique, Rint = 0.0786), 420 parameters, R1 [IϾ2σ(I)] = 0.0458, wR2
(all data) = 0.1290, largest diff. peak and hole: 0.87 and –0.90 eÅ–3.
1
171.0116; found 171.0119. I: H NMR (300 MHz, 298 K, CDCl3):
δ = 11.7 (br. s,1 H, NH), 8.30 (s, 1 H, CH=), 7.79 (d, J = 7.8 Hz,
2 H, anion), 7.44–7.32 (m, 5 H, Harom), 7.18 (d, J = 7.8 Hz, 2 H,
anion), 5.69 (s, 2 H), 2.84 (m, 1 H), 2.37 (s, 3 H, CH3 anion), 1.95
(m, 2 H), 1.66 (m, 3 H), 1.35–1.14 (m, 5 H) ppm. 13C NMR
(75 MHz, 298 K, CDCl3): δ = 149.4, 141.0, 140.8, 132.0 (Carom),
132.0, 129.6, 129.3, 129.2, 129.0, 126.1, 125.0 (Carom), 56.8 (CH2),
33.1 (CH), 31.6 (CH2), 25.4 (CH2), 25.1 (CH2), 21.4 (CH3) ppm.
HRMS (ES+, MeOH): calcd. for C15H20N3 [M – OTs]+ 242.16;
found 242.2.
Complex RhB: To a solution of B (117.6 mg, 0.20 mmol) in CH2Cl2
(5 mL) was added Ag2O (23.2 mg, 0.10 mmol). The mixture was
stirred at room temperature for 2 h and filtered through Celite. The
solvent was removed in vacuo at room temperature to give a white
Crystallographic Data for 4b: The intensity data were collected at
low temperature [180(2) K] with a Gemini Agilent Technologies
solid. [Rh(cod)Cl]2 (24.7 mg, 0.05 mmol) and CH2Cl2 (5 mL) were diffractometer equipped with an enhance Cu-Kα (λ = 1.5418 Å)
added, and the mixture was stirred at room temperature overnight.
The solution was filtered through Celite and evaporated at room
temperature to dryness, and the residue was washed with diethyl
ether and dried in vacuo to afford RhB as a yellow powder; yield
68.5 mg (97%). Single crystals were obtained by slow evaporation
source; φ and ω scans were used. The structure was solved by direct
methods by using SIR92[29] and refined by using the least-squares
method on F2 with SHELXL-97.[30] All non-H atoms were treated
anisotropically, and the H atoms were refined by using a riding
model. Selected crystal data: C17H22O2, M = 258.35, monoclinic,
space group P21, a = 9.249(5) Å, b = 5.547(5) Å, c = 14.597(5) Å,
1
of an acetonitrile solution. H NMR (300 MHz, 298 K, CDCl3): δ
= 7.32–7.38 (m, 8 H, Harom), 7.11–7.13 (m, 5 H, Harom), 6.08 [d, α = 90°, β = 102.052(5)°, γ = 90°, V = 732.4(8) Å3, Z = 2, crystal
JH,Rh = 14.6 Hz, 1 H, 22-H(a)], 5.80 [d, JH,Rh = 14.6 Hz, 1 H, 22- size 0.16ϫ0.12ϫ0.04 mm, 4604 reflections collected (2004 inde-
H(b)], 4.97 [d, JH,Rh = 15.0 Hz, 1 H, 19-H (a)], 4.86 [d, JH,Rh
=
pendent, Rint = 0.0381), 175 parameters, R1 [IϾ2σ(I)] = 0.0387,
wR2 (all data) = 0.0842, largest diff. peak and hole: 0.121 and
3.2 Hz, 1 H, 9-H9, 10-H (a)], 4.69–4.80 (m, 2 H, CHcod), 4.64 [d,
JH,Rh = 3.2 Hz, 1 H, 9-H, 10-H (b)], 4.04 (s, 3 H, 23-H), 3.61 [d, –0.143 eÅ–3.
JH,Rh = 15.0 Hz, 1 H, 19-H (b)], 3.52–3.56 [m, JH,Rh = 3.3 Hz, 1
CCDC-919100 (for A), -922794 (for RhB) and -930530 (for 4b)
H, 15-H, 16-H (a)], 3.32–3.36 [m, JH,Rh = 3.3 Hz, 1 H, 15-H, 16-
H (b)], 3.15–3.27 (m, 2 H, Hcod), 2.88 (m, 1 H, Hcod), 2.49–2.69
(m, 2 H, Hcod), 2.24–2.29 (m, 1 H, Hcod), 2.02–2.10 (m, 1 H, Hcod),
1.81 (m, 3 H, Hcod) ppm. 13C NMR (75 MHz, 298 K, CDCl3): δ =
177.5, 175.8 (C=O), 173.4 (d, JC,Rh = 46.6 Hz, C-21), 141.5, 141.4,
139.6, 139.5 (C-11–C-14), 137.2, 134.9 (C-20 and CPh), 128.7,
128.3, 126.7, 126.6, 126.5 (Carom), 124.8, 124.2 (d, JC,Rh = 10 Hz,
CHPh), 97.8 (d, JC,Rh = 7 Hz, Ccod), 97.5 (d, JC,Rh = 7 Hz, Ccod),
69.2 (d, JC,Rh = 15 Hz, Ccod), 67.6 (d, JC,Rh = 15 Hz, Ccod), 58.6
(C-22), 48.4, 47.2 (C-15, C-16), 45.3, 45.1 (C-9, C-10), 36.5 (C-23),
32.8, 32.5 (CH2 cod), 32.0 (C-19), 28.9, 28.4 (CH2 cod) ppm. IR
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
General Procedure for Rh-Catalyzed 1,4-Addition to α,β-Unsatu-
rated Carbonyl Compounds: To an oven-dried Schlenk tube under
an argon atmosphere, RhB (3.5 mg, 0.005 mmol), boronic acid
(0.6 mmol; 73.2 mg of a; 91.2 mg of b; 114 mg of c; 81.6 mg of
0.6 mmol), KOH (21 mg, 0.375 mmol), toluene (0.5 mL) and the
corresponding substrate (0.5 mmol; 104 mg of 1; 48 μL of 2; 42 μL
of 3; 78 μL of 4) were successively introduced. The mixture was
stirred for 24 h at 40 °C. The reaction mixture was then filtered
through a short column of Celite and eluted with diethyl ether. The
solvent of the organic phase was removed under reduced pressure,
and the resulting residue analyzed by GC and 1H NMR spec-
troscopy.
(KBr): ν = 3034 (=C–H), 2934 (C–H), 1707 (C=O), 1466 (C=C)
˜
cm–1. HRMS (ES+, acetonitrile): calcd. for C37H36N4O2Rh [M]+
671.1893; found 671.1889.
Crystallographic Data for A: The intensity data were collected at
193(2) K with a Bruker-AXS APEX II Quazar diffractometer
equipped with a 30 W air-cooled microfocus source (ImS) with fo-
Eur. J. Org. Chem. 2014, 2160–2167
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2165

E. Peris, M. Gómez, et al.
FULL PAPER
[5]
[6]
M. Sakai, H. Hayashi, N. Miyaura, Organometallics 1997, 16,
4229–4231.
Catalytic Procedure for C-Catalyzed Hetero-Michael Addition to 2-
Cyclohexenone: To an oven-dried Schlenk tube under an argon at-
mosphere, urethane (53.4 mg, 0.6 mmol), C (6.2 mg, 0.01 mmol),
CH2Cl2 (0.25 mL) and 2-cyclohexenone (48 μL, 0.5 mmol) were
successively added. The resulting mixture was stirred at room tem-
perature for 24 h. Extractions with diethyl ether (3ϫ5 mL) were
then performed, and the solvent was evaporated under reduced
pressure. The resulting residue was purified through a short column
For selected works, see: a) T. Hayashi, K. Ueyama, N. Tokun-
aga, K. Yoshida, J. Am. Chem. Soc. 2003, 125, 11508–11509;
b) C. Fischer, C. Defieber, T. Suzuki, E. M. Carreira, J. Am.
Chem. Soc. 2004, 126, 1628–1629; c) C. Defieber, J.-F. Paquin,
S. Serna, E. M. Carreira, Org. Lett. 2004, 6, 3873–3876; d) F.-
X. Chen, A. Kina, T. Hayashi, Org. Lett. 2006, 8, 341–344; e)
K. Okamoto, T. Hayashi, V. H. Rawal, Org. Lett. 2008, 10,
4387–4389.
1
of silica and analyzed by GC and H NMR spectroscopy.
[7]
[8]
a) T. Korenanga, K. Osaki, R. Maenishi, T. Sakai, Org. Lett.
2009, 11, 2325–2328; b) F. Berhal, O. Esseiva, C.-H. Martin,
H. Tone, J.-P. Genet, T. Ayad, V. Ratovelomanana-Vidal, Org.
Lett. 2011, 13, 2806–2809; c) T. Korenaga, R. Maenishi, K.
Hayashi, T. Sakai, Adv. Synth. Catal. 2010, 352, 3247–3254.
a) J.-G. Boiteau, R. Imbos, A. J. Minnaard, B. L. Feringa, Org.
Lett. 2003, 5, 681–684; b) K. Kurihara, N. Sugishita, K. Osh-
ita, D. Piao, Y. Yamamoto, N. Miyaura, J. Organomet. Chem.
2007, 692, 428–435.
B. J. Truscott, G. C. Fortman, A. M. Z. Slawin, S. P. Nolan,
Org. Biomol. Chem. 2011, 9, 7038–7041.
T. Hayashi, M. Takahashi, Y. Takaya, M. Ogasawara, J. Am.
Chem. Soc. 2002, 124, 5052–5058.
For selected reviews, see: a) D. Enders, C. Grondal, M. R. M.
Hüttl, Angew. Chem. 2007, 119, 1590; Angew. Chem. Int. Ed.
2007, 46, 1570–1581; b) C. Bhnaja, S. Jena, S. Nayak, S. Mo-
hapatra, Beilstein J. Org. Chem. 2012, 8, 1668–1694, and refer-
ences cited therein.
F. Han, L. Yang, A. Li, C. Xia, Org. Biomol. Chem. 2012, 10,
346–354.
a) D. Sanhes, I. Favier, N. Saffon, E. Teuma, M. Gómez, Tetra-
hedron Lett. 2008, 49, 6720–6723; b) D. Sanhes, E. Raluy, S.
Rétory, N. Saffon, E. Teuma, M. Gómez, Dalton Trans. 2010,
39, 9719–9726; c) I. Bratko, S. Mallet-Ladeira, N. Saffon, E.
Teuma, M. Gómez, Dalton Trans. 2013, 42, 1136–1143; d) I.
Bratko, M. Gómez, Dalton Trans. 2013, 42, 10664–10681.
a) B. Royo, E. Peris, Eur. J. Inorg. Chem. 2012, 1309–1318; b)
R. Corberan, E. Mas-Marza, E. Peris, Eur. J. Inorg. Chem.
2009, 1700–1716; c) J. A. Mata, M. Poyatos, E. Peris, Coord.
Chem. Rev. 2007, 251, 841–859; d) M. Poyatos, J. A. Mata, E.
Peris, Chem. Rev. 2009, 109, 3677–3707.
General Procedure for Triazolium-Catalyzed Hetero-Michael Ad-
dition to α,β-Unsaturated Ketones: To an oven-dried Schlenk tube
under an argon atmosphere, nucleophile (32.0 mg, 0.36 mmol of e;
48.5 μL, 1.2 mmol of f; 44.6 mg, 0.36 mmol of g), A (2.7–13.4 mg,
0.006–0.03 mmol), TsOH·H2O (1.1–5.7 mg, 0.006–0.03 mmol),
CH2Cl2 (0.25 mL) and the corresponding substrate (0.3 mmol;
29 μL of 2; 25.1 μL of 3; 46.9 μL of 4) were successively added.
The resulting mixture was stirred at room temperature for 24 h.
Extractions with diethyl ether (3ϫ5 mL) were then performed, and
the solvent was evaporated under reduced pressure. The resulting
residue was purified through a short column of silica and analyzed
[9]
[10]
[11]
1
by GC and H NMR spectroscopy.
Supporting Information (see footnote on the first page of this arti-
cle): Spectral data for the organic products of the catalytic reac-
tions; Figure S1: 1H NMR spectra for A–C; Figure S2: X-ray crys-
tal structure for A; Figure S3: modelled RhB conformers; Figure
S4: 1H NMR spectrum for 4b; Figure S5: NOESY NMR spectrum
[12]
[13]
1
for 4b; Figure S6: X-ray crystal structure for 4b; Tables S1–S4; H
and 13C NMR spectra for II, A, B, C, E, RhB, 1a, 1b, 2a, 2b, 2d,
2e, 2g, 3a, 3b, and 4b.
Acknowledgments
[14]
Financial support from the Centre National de la Recherche Sci-
entifique (CNRS), the Université Paul Sabatier, the Spanish Minis-
terio de Ciencia e Innovación (MICINN) (grant number CTQ2011-
24055/BQU) and Bancaixa (grant number P1.1B2010-02) are ac-
knowledged. The authors are grateful to the Serveis Centrals d’In-
strumentació Científica (SCIC) for spectroscopic facilities (Uni-
versitat Jaume I - Spain). I. B. thanks the Ministère de l’Enseigne-
ment Supérieur et de la Recherche for a PhD grant. The authors
are grateful to Dr. José A. Mata for the X-ray diffraction analysis
of RhB.
[15]
[16]
V. V. Rostovtsev, L. G. Green, V. V. Fokin, K. B. Sharpless, An-
gew. Chem. 2002, 114, 2708; Angew. Chem. Int. Ed. 2002, 41,
2596–2598.
a) G. Ung, G. Bertrand, Chem. Eur. J. 2011, 17, 8269–8272; b)
A. Kruger, M. Albrecht, Aust. J. Chem. 2011, 64, 1113–1117; c)
G. Guisado-Barrios, J. Bouffard, B. Donnadieu, G. Bertrand,
Angew. Chem. 2010, 122, 4869; Angew. Chem. Int. Ed. 2010,
49, 4759–4762; d) P. Mathew, A. Neels, M. Albrecht, J. Am.
Chem. Soc. 2008, 130, 13534–13535; e) K. F. Donnelly, A. Pe-
tronihlo, M. Albrecht, Chem. Commun. 2013, 49, 1145–1159;
f) J. Bouffard, B. K. Keitz, R. Tonner, G. Guisado-Barrios, G.
Frenking, R. H. Grubbs, G. Bertrand, Organometallics 2011,
30, 2617–2627.
J.-F. Paquin, C. Defieber, C. R. Stephenson, E. M. Carreira, J.
Am. Chem. Soc. 2005, 127, 10850–10851.
W. C. Trenkle, J. L. Barkin, S. U. Son, D. A. Sweigart, Organo-
metallics 2006, 25, 3548–3551.
I. Penafiel, I. M. Pastor, M. Yus, M. A. Esteruelas, M. Olivan,
Organometallics 2012, 31, 6154–6161.
In two cases only, small amounts of byproducts were observed
(2% of the homocoupling product from the boronic acid was
detected in the formation of 2c, and 9% of the deboronation
product was detected for 4b; Table 1, Entries 6 and 11).
With [RhCl(cod)]2 as catalyst precursor and toluene as solvent,
the 1,4-addition product 8 was mainly obtained (52% yield; 6
was concomitantly obtained in 18% yield) after 24 h of reac-
tion, in contrast to the reported data with THF as solvent: C.-
H. Xing, T.-P. Liu, J. R. Zheng, J. Ng, M. Esposito, Q.-H. Hu,
Tetrahedron Lett. 2009, 50, 4953–4957.
[1] a) R. Ballini, L. Barboni, G. Bosica, D. Fiorini, A. Palmieri,
Pure Appl. Chem. 2007, 78, 1857–1866; b) R. Brehme, D. En-
ders, R. Fernandez, J. M. Lassaletta, Eur. J. Org. Chem. 2007,
5629–5660; c) P. Tian, H.-Q. Dong, G.-Q. Lin, ACS Catal.
2012, 2, 95–119.
[2] For selected reviews and relevant examples, see: a) K. Fagnou,
M. Lautens, Chem. Rev. 2003, 103, 169–196; b) T. Hayashi, K.
Yamasaki, Chem. Rev. 2003, 103, 2829–2844; c) L. Zhao, Y.
Ma, F. He, W. Duan, J. Chen, C. Song, J. Org. Chem. 2013, 78,
1677–1681; d) V. Lillo, A. Prieto, A. Bonet, M. M. Diaz-Re-
quejo, J. Ramirez, P. J. Pérez, E. Fernández, Organometallics
2009, 28, 659–662; e) H.-C. Guo, J.-A. Ma, Angew. Chem. 2006,
118, 362; Angew. Chem. Int. Ed. 2006, 45, 354–366; f) H. Wu,
S. Radomkit, J. M. O’Brien, A. H. Hoveyda, J. Am. Chem. Soc.
2012, 134, 8277–8285.
[17]
[18]
[19]
[20]
[21]
[3] T. Jerphagnon, M. G. Pizzuti, A. J. Minnaard, B. L. Feringa,
Chem. Soc. Rev. 2009, 38, 1039–1075, and references cited
therein.
[4] For a selected review, see: H. J. Edwards, J. D. Hargrave, S. D.
Penrose, C. G. Frost, Chem. Soc. Rev. 2010, 39, 2093–2105.
2166
www.eurjoc.org
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2014, 2160–2167

Triazolium Salts as Catalytic Scaffolds for 1,4-Additions
[22] It is important to note that C is an inactive catalyst (10 mol-% [27] L. Campbell-Verduyn, P. H. Elsinga, L. Mirfeizi, R. A. Di-
of catalyst) for the addition of dimethylmalonate or the boronic
acid b to 2-cyclohexenone.
erckx, B. L. Feringa, Org. Biomol. Chem. 2008, 6, 3461–3463.
[28] R. Grigg, V. Sridharan, D. A. Sykes, Tetrahedron 2008, 64,
8952–8962.
[29] SAINT and SADABS, Bruker AXS Inc., Madison WI, 2008.
[30] SHELXL-97, Program for Crystal Structure Refinement, G. M.
Sheldrick, University of Göttingen, Germany; see: Acta Crys-
tallogr. Sect. A 2008, 64, 112.
[23] For theoretical studies concerning the regioselective proton-
ation of 1,2,3-triazole compounds, see: O. A. Ivashkevich, V. E.
Matulis, P. N. Gaponik, G. T. Sukhanov, J. V. Filippova, A. G.
Sukhanova, Chem. Heterocycl. Compd. 2008, 12, 1472–1482.
[24] X. Xiong, L. Cai, Catal. Sci. Technol. 2013, 3, 1301–1307.
[25] Y. M. A. Yamada, S. M. Sarkar, Y. Uozumi, J. Am. Chem. Soc.
2012, 134, 9285–9290.
[31] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J.
Appl. Crystallogr. 1993, 26, 343–350.
[26] F. Alonso, Y. Moglie, G. Radivoy, M. Yus, Tetrahedron Lett.
2009, 50, 2358–2362.
Received: August 13, 2013
Published Online: January 27, 2014
Eur. J. Org. Chem. 2014, 2160–2167
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2167