Pd(NHC)-catalyzed alkylsulfonylation of boronic acids: A general and efficient approach for sulfone synthesis

Article abstract of DOI:10.1039/c7cc05851a

Robust N-heterocyclic carbene palladium complexes are highly efficient catalysts for direct alkylsulfonylation of (hetero)aryl- or alkenyl-boronic acids with potassium metabisulfite and (hetero)alkyl-halides. Among them, acenaphthoimidazolylidene palladium(ii) complexes exhibited the highest activities, and up to quantitative yields were obtained for diverse structurally distinct sulfones under very mild reaction conditions.

Full text of DOI:10.1039/c7cc05851a

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Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc3N@C2n (2n 68 and 80). Synthesis of the
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Pd(NHC)-Catalyzed Alkylsulfonylation of Boronic Acids: A General
and Efficient Approach for Sulfone Synthesis†
Haibo Zhu,a Yajing Shen,a Qinyue Deng,a Jinjin Chen*c and Tao Tu*ab
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Robust N-heterocyclic carbene palladium complexes are highly electrophiles is compatible with sensitive functional groups.9
efficient catalysts for direct alkylsulfonylation of (hetero)aryl- or However, there is only one recent report that indicates that
alkenyl- boronic acids with potassium metabisulfite and the C-electrophile could be added at the start of the reaction
(hetero)alkyl-halides. Among them, acenaphthoimidazolylidene along with other substances,10 where a 10 mol% catalyst
palladium(II) complexes exhibited the highest activities, and up to loading was required. Despite these achievements, the
quantitative yields were obtained for diverse structurally distinct development of general and direct sulfones synthesis from
sulfones under very mild reaction conditions.
diverse readily available boronic acids at low catalyst loading
with excellent yields and selectivity under mild reaction
conditions is still highly desirable. To the best of our
knowledge, there is no example of a Pd(NHC) catalyzed
sulfonylation reaction. Building on our recent study that
As a versatile protocol to construct C-C and C-X bonds,
Pd(0)-catalyzed cross-coupling reactions constitute one of best
options in organic synthesis,1 especially with readily available
and low-toxicity aryl boronic acids.2 Benefiting from the
development of ligand design, the feasibility of such protocols
has been demonstrated in the classic cross-coupling reactions,
and also exhibited high selectivity in the related carbonylation
tranformations.3 In contrast with intensively investigated air-
sensitive phosphines, robust N-heterocyclic carbene (NHC)
ligands sometimes exhibited better catalytic activity for such
kinds of transformations.4,5 One possible explanation is the
demonstrated
acenaphthoimidazolylidene
palladium
complexes exhibit extremely high catalytic activity toward
sterically hindered cross-coupling reactions11 and direct
carbonylation reactions,12 herein we report a robust and
general catalytic protocol for direct alkylsulfonylation of aryl-
and alkenyl- boronic acids with K2S2O5 and diverse C-
electrophiles
with
low
catalyst
loadings
of
acenaphthoimidazolylidene palladium complexes..
strong σ-donor property of NHCs, which can improve retain Pd
Direct alkylsulfonylation of 4-tolylboronic acid by tert-butyl
centre during the transformation. Consequently, well-defined
Pd(NHC) species can deliver longer lifetimes and consistent
efficiency.5
bromoacetate was selected as a model reaction to evaluate
the catalytic activity of Pd(NHC) complexes 1a-c and 2, which
were synthesized according to the reported procedures.11,13 In
the presence of 5 mol% of allylic Pd(NHC) complex 1a and
tetrabutylammonium bromide (TBAB) in DCE at 100 oC after 24
hours, produced 3a was in a yield of 20% (Table 1, entry 1).
However, the yield dramatically increased to 71% when
nonpolar toluene was used (Table 1, entry 2). Quantitative
transformation was achieved with dioxane as a solvent (Table
1, entry 3). Other polar and nonpolar solvents resulted in
inferior results (See ESI†) and no product was detected when
the reaction was carried out in methanol or DMSO. Besides
Sulfone groups are present in numerous functional
molecules of agrochemical, pharmaceutical or material
significances.6 The success of the Pd-catalyzed carbonylation
reactions7 has been extended to the analogous sulfonylative
cross-coupling reaction due to their similar electronic and
coordination properties between carbon monoxide and sulfur
dioxide.8 In contrast to conventional oxidative methods, the
Pd-catalyzed sulfonylation of aryl boronic acids with C-
allylic ligands, other “throw away″
ligands14 anchored on the
Pd(NHC) complexes 1b and 1c only showed slightly impact on
the transformation (Table 1, entries 3 and 4). In the case of
catalyst containing 3-chloro pyridine (1c), a 90% yield of 3a
was obtained under in dioxane at 100 oC after 24 hours.
However, the allylic catalyst derived from imidazolium
analogue (
2), which has been proven as a highly active catalyst
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in a number of coupling reactions,15 was applied, the yield tolylboronic acid partially affected the transformation
decreased into 85% (Table 1, entry 6 vs entry 3). This result is efficiency. In contrast to p-tolylboronic acid that 96% yield of
consistent with our previous observation that ylidenes derived sulfone 3a was obtained, products 3b and 3c were produced
from acenaphtho-imidazolyium salts exhibit higher catalytic with yields of 90% and 60%, respectively, from the
activity than their imidazolium analogues due to the stronger corresponding meta- and ortho- isomers. Other mono- and di-
σ-donor and weaker π-acceptor properties.11,12
electron-neutral, rich and poor substitutes were all compatible
4-7), and up to quantitative yields were obtained. Halo-
(
Table 1. Optimization of the reaction conditionsa
substituted boronic acids were also fully tolerated. Remarkably,
in the case of chlorinated substrate, no direct Suzuki-coupling
products was formed, although complex 1a is efficient catalyst
for both transformations.11b Sulfone 6b was produced in a 86%
yield, which not only provided the opportunity for further
transformation, but also highlighted the chemoselectivity of
the newly developed catalytic system.
Entry
[Cat.]/mol%
Solvent
Yield (%)b
1
2
1a /5
1a /5
DCE
20
71
>99
98
90
85
74
85
62
15
80
47
NR
Toluene
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Table 2. Reaction of tert-butyl bromoacetate with various hetero(aryl)boronic acidsa
3
1a /5
4
1b/5
5
1c/5
6
2/5
O
O
O
O O
S
O O
S
O O
S
R
OtBu
OtBu
OtBu
7
PdCl2/5
PdCl2/PPh3/5
Pd(OAc)2/5
Pd2(dba)3/5
1a/2
H3C
R
R
8
3a: 96% (p-)
3b: 90% (m-)
3c: 60% (o-)
4a: 99% (R = tBu)
4b: 90% (R = OMe)
4c: >99% (R = Ph)
4d: 93% (R = OCF3)
R
5a: 92% (R = H)
5b: 94% (R= Me)
5c: 85% (R = F)
9
10
11
12
13
O
O
O
O O
S
O O
S
O O
S
OtBu
OtBu
OtBu
R
S
1a/1
7a: 72% (R = CO2Et)c
7b: 72% (R = NHBoc)c
6a: 95% (R = F)
6b: 86% (R = Cl)
8: 85%
/
O
O O
S
a
Reaction was carried with 5 mol% catalyst, 4-Methylphenylboronic acid (0.5 mmol),
O
O
O O
S
O O
S
OtBu
K2S2O5 (2.0 equiv.), TBAB (1.1 equiv.), and tert-butyl bromoacetate (2.0 equiv.) in 2 mL
solvent at 100 oC for 24 hours. b Isolated yield.
OtBu
OtBu
N
N
S
O O
Dipp
Dipp
Cl
10a: 91% (1-naphthalenyl-)
10b: >99% (2-naphthalenyl-)
10c: 99% (9-phenanthrenyl-)
11: 77%c
Cl
9: 65%
N
N
N
Dipp
N
Dipp
Pd
Pd
N
R1
Dipp:
iPr
iPr
Pd
2
N
Dipp
N
Cl
Cl
O
O
O
Cl
O O
S
O O
O O
Dipp
S
S
O
O
OtBu
OtBu
OtBu
1a:
R
1 = H;
1b: R1 = Ph
1c
S
O
12: 79%
13: 83%
14: 85%
O
O
O
O O
S
O O
S
O O
S
OtBu
OtBu
OtBu
The NHC ligand is crucial for the alkylsulfonylation process.
When palladium salts such as PdCl2 and Pd(OAc)2 were applied
directly, moderate to good yields were achieved (74% and
62%, Table 1, entries 7 and 9), whereas, Pd(0) precatalyst like
Pd2(dba)3 resulted in even worse outcomes (15%, Table 1,
entry 1), indicating that the Pd(II) species and redox-neutral
pathway may be responsible for this transformation. When 5
mol% triphenylphosphine was added along with PdCl2, a
S
15: 87%
17: 79%
16: 68%
a Reaction was carried with 5 mol% 1a, 4-Methylphenylboronic acid (0.5 mmol), K2S2O5
(2.0 equiv.), TBAB (1.1 equiv.), and tert-butyl bromoacetate (2.0 equiv.) in 2 mL dioxane
at 100 oC for 24 hours. b Isolated yield. c With 5 mol% of Pd(NHC) complex 1c.
We further expanded the substrate scope to the ester and
amide groups by using 1c, which produced the desired
products 7a and 7b in good yields (72%). In the case of
challenging substrate containing sulfide group, 4-
thiomethylphenylboronic acid, an unexpected excellent yield
compatible yield with complex
2 could be observed (85%,
Table 1, entry 8), supporting the role of the ligands. The yields
decreased when lower catalyst loadings of Pd(NHC) complex
1a was applied (80% and 47%, entries 11 and 12, respectively).
As expected, no reaction took place in when no palladium was
added under the optimized reaction conditions (entry 13,
Table 1).
was obtained for the production of sulfide-sulfone
8 (85%), a
product usually difficult to prepared using the conventional
oxidative or other coupling methodologies. 4-(Methylsulfonyl)-
phenylboronic acid with a strong electron-withdrawing group
was also good substrate to produce sulfone
Although, ortho-tolylboronic acid resulted in a moderate yield
3c), aryl boronic acids with extended conjugated system were
9 in a 65% yield.
We next tested the feasibility of the protocol with a variety
of (hetero)aryl and alkenyl boronic acids, and the results are
summarized in Table 2. Both electron-rich and electron-
deficient substituents on the phenyl ring of boronic acids were
(
all converted to the corresponding products in excellent to
quantitative yields (10a-c, 91->99%). Similar outcomes were
also observed from the reactions with heterocyclic substrates,
well tolerated (Table 2,
3-9) under the optimized reaction
conditions, however, the position of the methyl group of
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and the challenging hetero-arylboronic acids containing N, O, S alkenyl groups, good to excellent yields were attained (23 and
atoms were all well accommodated, and good yields were 24, 87% and 80%, respectively). Primary alkyl bromides, 2-
obtained for the corresponding sulfones (11-13). As sulfide- bromoacetophenone, benzyl 2-bromoacetate and ethyl 2-
sulfones are difficult to access by conventional oxidation bromoacetate were all suitable electrophiles to afford the
approaches, 3-thiophene and dibenzo[b,d]thiophen-2-yl sulfone products (25a-b, 26, 87%, 95% and 97%, respectively).
boronic acids were also studied, and good yields were An 80% yield (4a) was reached with inactive tert-butyl 2-
obtained even considering strong coordination ability of this chloroacetate, further highlighting the protocol efficiency.
substrates to Pd (14 and 15, 85% and 87%, respectively). Amide groups were also well tolerated where active or inactive
Challenging alkenyl boronic acids were also considered as electrophiles were involved (27 and 28). Using the standard
suitable
substrates
for
this
protocol,
and
E- reaction conditions for inert n-alkyl bromides, good yields for
phenylethenylboronic acid and the 1-cyclohexenylboronic acid the desired aryl alkyl sulfone were observed (29a
were converted to the corresponding alkenyl-alkyl products in 87%) in the presence of 10 mol% catalyst loading.
good yields (16 and 17, 68% and 79%, respectively).
-b, 82% and
Table 3. Reaction scope with various C-electrophilesa
Scheme 1. Control experiments for plausible mechanism investigation.
To investigate the plausible reaction mechanism, several
control experiments were carried out (Scheme 1). When
TEMPO, a radical scavenger, was added into the reaction
mixture containing Pd(NHC) 1a, phenyl boronic acid and tert-
butyl bromoacetate under the standard reaction conditions,
sulfone 5a was still obtained in an 80% yield (Eq. 1, Scheme 1).
Combining the outcomes from Pd salts (Table 1, entries 7, 9
and 10), the Pd(II) species may be a true active intermediate.
However, extensive efforts aiming to isolate the possible
intermediates from the reaction mixture with stoichiometric
a
Reaction was carried with 5 mol% 1a, 4-tert-butylphenylboronic acid (0.5 mmol),
K2S2O5 (2.0 equiv.), TBAB (1.1 equiv.), and electrophile (2.0 equiv.) in 2 mL Dioxane at
100 oC for 24 hours. b Isolated yield. c With 10 mol% of Pd(NHC) complex 1c.
amount of Pd(NHC) complex 1a, 1c or 2 have been proved to
be unsuccessful. When less bulky PPh3 was applied instead of
NHC ligands, dimeric Pd(II) complex 30 was isolated. With this
complex in hand, a stoichiometric reaction with tert-butyl
bromoacetate was carried out under the standard reaction
conditions; sulfone 5a was produced in a yield of 87% after 12
hours (Eq. 2, Scheme 1). Unlike previous Pd-catalyzed
alkylsulfonylation with phosphine ligands,9 no possible routine
sulfinates were detected in this stoichiometric reaction. When
5 mol% dimeric complex 30 was used as a catalyst without
Inspired by the excellent outcomes obtained with a range of
(hetero)-aryl and alkenyl boronic acids, we then focused on
the scope of C-electrophiles (Table 3). This investigation
showed that beside reactive α-bromoacetates, less active
benzyl bromide and benzyl chloride were all competent
substrates to access sulfone 18 (94% and 80%, respectively).
Various electronic-donating and electronic-withdrawing
substitutes on the phenyl ring of benzyl bromides were also
well tolerated, and good to excellent yields were provided (79-
99%, 19-21). Among these the electron-withdrawing
substrates containing -NO2, -CN or -F substitutes were more
active (79-96%, 19c-21). The relative position of substituents
of the electrophiles did not hamper the catalytic efficiency,
and only slightly different yields were found with ortho-, meta-,
para-isomers (20a-c, 91-96%). Good yield was still provided
additional ligands, a yield of 91% for sulfone
5 was obtained
(Eq. 3, Scheme 1), highlighting this dimeric species may be the
true active species in the catalytic cycle.
Single crystals suitable for X-ray diffraction analysis were
obtained by slow diffusion of ether to the solution of dimeric Pd(II)
complex 30 in CH2Cl2 (Fig. 1), which may help us to better
understand the mechanism. The Pd-S bond length is relative long
(2.2516(17) Å), and 0.116 Å longer than the corresponding Pd-S
bond in the known anionic dimeric Pd(II) complex,10 suggesting this
intermediate is more reactive in the presence of electrophile.
Interestingly, although phosphine ligands are bulky, the phenyl
group attached in S atom keep in same side with phosphine
with inactive 4-fluorobenzyl chloride
(21, 82%). When
electron-rich and bulky 2-(bromomethyl)naphthalene was
investigated, sulfone 22 was obtained in a 94% yield. In the
case of active methyl 4-(bromomethyl)benzoate and methyl 3-
(4-bromomethyl)-cinnamate, which have both ester and
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resulting the torsion angle between two Cl-Pd-Cl planes is 129.6o, Shanghai International Cooperation Program (14230710600),
due to C-H···π interactions (the shortest one is 2.495 Å). This data and Department of Chemistry, Fudan University is gratefully
suggests the reactive dimeric complex is liable to dissociate, which acknowledged.
makes the electrophile trapping more easy (blue arrows in Fig. 1b).
With these two crucial information in hand, we propose that the
Notes and references
congested dimeric Pd(II) intermediate may be released after the
alkylation, which accelerate the conversion process leading to the
sulfone formation in good yields.2b
1
(a) Handbook of Organopalladium Chemistry for Organic
Synthesis (Ed.: E.-i. Negishi), Wiley: New York, 2002; (b) A. de
Meijere, F. Diederich in Metal-Catalyzed Cross-Coupling
Reactions, Vol. 1, 2nd. ed. (Ed.: N. Miyaura), Wiley-VCH,
Weinheim, 2004, pp. 41-123; (c) Metal-Catalyzed Cross-
Coupling Reactions and More (Eds.: A. de Meijere, S.Brase,
M. Oestreich), Wiley: New York, 2014.
2
3
(a) N. Miyaura, K. Yamada and A. Suzuki, Tetrahedron Lett.,
1979, 20, 3437-3440; (b) N. Miyaura and A. Suzuki, Chem.
Rev., 1995, 95, 2457-2483.
(a) X.-F. Wu, H. Neumann and M. Beller, Chem. Soc. Rev.,
2011, 40, 4986-5009; (b) X.-F. Wu, H. Neumann and M.
Beller, Chem. Rev., 2013, 113, 1-35; (c) S. D. Friis, A. T.
Lindhardt and T. Skrydstrup, Acc. Chem. Res., 2016, 49,
594−605.
4
(a) F. E. Hahn, Angew. Chem., Int. Ed., 2006, 45, 1348-1352;
(b) S. Würtz and F. Glorius, Acc. Chem. Res., 2008, 41, 1523-
1533; (c) F. E. Hahn and M. C. Jahnke, Angew. Chem., Int. Ed.,
2008, 47, 3122-3172; (d) M. N. Hopkinson, C. Richter, M.
Schedler and F. Glorius, Nature, 2014, 510, 485-496.
(a) N-Heterocyclic Carbenes in Transition Metal Catalysis;
Top. Organomet. Chem. (Ed.: Glorius, F.) Springer-Verlag,
Berlin/Heidelberg, 2007, pp. 28. (b) N-Heterocyclic Carbenes
(Ed.Nolan, S. P.) Wiley: Weinheim, Germany, 2014.
(a) The Chemistry of Sulfones and Sulfoxides (Eds.: S. Patai, Z.
Rappoport, C. J. M. Stirling) Wiley: New York, 1988; (b)
Sulfones in Organic Synthesis (Ed.: N. S. Simpkins) Pergamon
Press: Oxford, 1993.
(a) W. Fang, H. Zhu, Q. Deng, S. Liu, X. Liu, Y. Shen and T. Tu,
Synthesis, 2014, 46, 1689-1708; (b) X.-F. Wu, RSC Adv., 2016,
6, 83831-83837; (c) J.-B. Peng, X. Qi and X.-F. Wu,
ChemSusChem, 2016, 9, 2279-2283; (d) X.-F. Wu, Chem. Eur.
J., 2015, 21, 12252-12265; (e) H.-Y. Zhao, F. Zhang, Z. Luo and
X. Zhang, Angew. Chem., Int. Ed., 2016, 55, 10401-10405.
G. J. Kubas, Acc. Chem. Res., 1994, 27, 183-190.
Fig. 1. a) Top view and b) side view of X-ray crystal structure of complex 30 (Ellipsoids
set at 50% probability, and the hydrogen atoms are omitted for clarity); c) the plausible
mechanism for the Pd(II)-catalyzed alkylsulfonylation of boronic acids.
5
6
7
Based on these results, a new plausible transformation
route is proposed (Fig. 1c). Initially, transmetalation takes
place between Pd(II) species and boronic acid,2b and follows by
the insertion of SO2 into the Pd-C bond16 to generate a dimeric
Pd(II) intermediate complex 30. Due to the bulky and
electronic rich properties of ligand, the long and accessible Pd-
S bond is easily attacked by C-electrophiles in the presence of
TBAB. Along with the corresponding sulfone product formation,
the ligated Pd(II) catalyst is regenerated. Combining the result
of Eq. 2 and the previous study,10 there may be two plausible
roles of TBAB in the transformation: 1) increasing the solubility
of the inorganic salt in dioxane and 2) accelerating the
transformation of dimeric Pd(II) intermediate like 30 into
sulfinate leading to the corresponding sulfone formation.
In conclusion, robust Pd(NHC) complexes have been
demonstrated for the first time as highly efficient catalysts in
the direct alkylsulfonylation of readily available (hetero)aryl- or
alkenyl-boronic acids with potassium metabisulfite and diverse
8
9
(a) P. Bisseret and N. Blanchard, Org. Biomol. Chem., 2013,
11, 5393–5398; (b) G. Liu, C. Fan and J. Wu, Org. Biomol.
Chem., 2015, 13, 1592–1599.
10 A. Shavnya, K. D. Hesp, V. Mascitti and A. C. Smith, Angew.
Chem., Int. Ed., 2015, 54, 13571-13575.
11 (a) T. Tu, W. Fang and J. Jiang, Chem. Commun., 2011, 12358-
12360; (b) T. Tu, Z. Sun, W. Fang, M. Xu and Y. Zhou, Org.
Lett., 2012, 14, 4250-4253.
12 (a) W. Fang, Q. Deng, M. Xu and T. Tu, Org. Lett., 2013, 15,
3678-3681; (b) S. Liu, Q. Deng, W. Fang, J.-F. Gong, M.-P.
Song, M. Xu and T. Tu, Org. Chem. Front., 2014, 1, 1261-
1265.
13 M. S. Viciu, O. Navarro, R. F. Germaneau, R. A. Kelly, W.
Sommer, N. Marion, E. D. Stevens, L. Cavallo and S. P. Nolan,
Organometallics, 2004, 23, 1629-1635.
14 (a) M.-T. Chen, D. A. Vicic, M. L. Turner and O. Navarro,
Organometallics, 2011, 30, 5052-5056; (b) F. Izquierdo, S.
Manzini and S. P. Nolan, Chem. Commun., 2014, 50, 14926-
14937.
15 M. S. Viciu, R. F. Germaneau, O. Navarro-Fernandez, E. D.
Stevens and S. P. Nolan, Organometallics, 2002, 21, 5470-
5472.
alkylhalides.
Remarkably,
acenaphthoimidazolylidene
palladium complexes exhibited the highest activity, and up to
quantitative yields could be obtained even at low catalyst
loading. Although it is difficult to isolate the intermediate
derived from the Pd(NHC) complexes, the crystal structure of a
dimeric Pd(II) analogue helps us to propose plausible
mechanism for this challenging transformation, in which
routine sulfinate intermediates may not be involved. This first
Pd(NHC)-catalyzed redox-neutral protocol presented a direct,
general, and efficient approach to access diverse (hetero)aryl-
alkyl and alkenyl-alkyl sulfones.
Financial support from the National Key R&D Program of
China (2016YFA0202902), National Natural Science Foundation
of China (No. 21572036, 81670810 and 91127041), the
16 D. P. Gates, P. S. White and M. Brookhart, Chem. Commun.,
2000, 47-48.
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O
O
5 mol% [Cat.]
R-B(OH)2
Alkyl-X
+
S
K2S2O5, TBAB
Dioxane, 100 o
R
Alkyl
R = (hetero)-aryl,
alkenyl
X = Br, Cl
C
[Cat.]
47
examples
up to>99% yield
N
N
Low catalyst loadings;
Mild reaction conditions;
Broad substrate scope
Pd
Cl
The first Pd(NHC) catalyzed direct alkylsulfonylation of boronic acids with K2S2O5 and alkyl halides has been successfully developed to afford
various functional sulfones under very mild reaction conditions at low catalyst loadings.
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