Development of C-N coupling using mechanochemistry: Catalytic coupling of arylsulfonamides and carbodiimides

Article abstract of DOI:10.1002/anie.201404120

Reported herein is the mechanochemical synthesis of sulfonyl guanidines, a family of molecules which are relevant as pharmaceuticals and herbicides, by direct coupling of sulfonamides and aromatic or aliphatic carbodiimides. Attempts to conduct the coupling in solution have either failed or given very low conversions, thus demonstrating mechanochemistry as the necessary component for the discovery of this synthetic strategy. Milling around: Mechanochemistry is used to develop a method for the direct coupling of carbodiimides and arylsulfonamides using a copper catalyst. Attempts to reproduce this C-N coupling reaction under conventional solution-based conditions either failed or gave very poor conversions.

Full text of DOI:10.1002/anie.201404120

Angewandte
Chemie
DOI: 10.1002/anie.201404120
Synthetic Methods
À
Development of C N Coupling Using Mechanochemistry: Catalytic
Coupling of Arylsulfonamides and Carbodiimides**
ˇ
ˇˇ ´
Davin Tan, Cristina Mottillo, Athanassios D. Katsenis, Vjekoslav Strukil, and Tomislav Friscic*
Abstract: Reported herein is the mechanochemical synthesis of
sulfonyl guanidines, a family of molecules which are relevant
as pharmaceuticals and herbicides, by direct coupling of
sulfonamides and aromatic or aliphatic carbodiimides.
Attempts to conduct the coupling in solution have either
failed or given very low conversions, thus demonstrating
mechanochemistry as the necessary component for the discov-
ery of this synthetic strategy.
a family of molecules which have significant potential as
herbicides and pharmaceuticals,[13–15] by catalytic coupling of
sulfonamides and carbodiimides (Scheme 1a). Such coupling
M
echanochemistry[1] is a rapidly developing approach to
environmentally friendly and solvent-free synthesis, and
offers excellent atom efficiency, reduction in energy con-
sumption,[2] and can expand the scope of chemical reactions
by allowing reactivity independent[3] of solubility. Selectivity
and stoichiometric control shown in mechanochemical reac-
tions[4,5] offer an opportunity for exhaustive[6] or site-selective
derivatization[7] of small molecules. The recent reports[8,9] of
multistep or multicomponent syntheses of complex targets[10]
suggest mechanochemistry can provide solvent-free chemis-
try with synthetic freedoms akin to those of solution synthesis.
Such development is particularly attractive to pharmaceutical
industries which demand more efficient and cleaner synthetic
methods.[11] However, a persistent critique of mechanosyn-
thesis is that, with rare exceptions,[12] its focus is on improving
known chemistry rather than on reaction discovery. Conse-
quently, mechanochemical reactions are often perceived as
a tool for making greening known solution-based reactivity,
rather than as a means for reaction discovery.
Scheme 1. a) A potential retrosynthetic route to N-sulfonylguanidines.
b) Reported coupling of 1 with DCC and DIC. c) Initial attempts to
react 2 and DCC by solution synthesis, neat milling, or LAG.
d) Successful LAG[20,21] synthesis catalyzed by 5 mol% CuCl.
is not normally observed because of poor sulfonamide
nucleophilicity. The unusual exception to this is trifluorome-
thylsulfonamide (1), which was recently found[16] to react with
di(cyclohexyl)carbodiimide (DCC) and diisopropylcarbodi-
imide (DIC; Scheme 1b). Normally, N-sulfonylguanidines are
obtained from activated sulfonyl or carbodiimide deriva-
tives.[14,17,18] Recently, however, we demonstrated the efficient
copper-catalyzed mechanochemical coupling of sulfonamides
and isocyanates,[19] and speculated as to whether similar
reactivity might be applicable to carbodiimides.
We now demonstrate mechanochemistry as the enabling
element of a new one-step route to N-sulfonylguanidines,
ˇ
ˇˇ ´
[*] D. Tan, C. Mottillo, Dr. V. Strukil, Prof. Dr. T. Friscic
Department of Chemistry and FRQNT Centre for Green Chemistry
and Catalysis, McGill University
801 Sherbrooke St. W. H3A 0B8 Montreal (Canada)
E-mail: tomislav.friscic@mcgill.ca
We first attempted the coupling of p-tolylsulfonamide (2)
with DCC to form the N-sulfonylguanidine 2a (Scheme 1c).
Attempts to conduct the coupling in solution or by milling
were not successful. These included liquid-assisted grinding
(LAG),[20,21] a mechanochemical technique which uses sub-
stoichiometric amounts of a liquid to enhance reactivity and
base-assisted synthesis, which previously enabled the mecha-
nosynthesis of sulfonyl-thioureas by milling 2 first with K2CO3
and then with the electrophile.[19]
Next, we attempted neat milling and LAG in the presence
of CuCl, which was previously shown to catalyze the
mechanochemical coupling of sulfonamides and isocya-
nates.[19] As shown by 1H NMR spectroscopy, adding
5 mol% of CuCl to the reaction mixture resulted in 81%
ˇ
Dr. V. Strukil
Laboratory for Physical Organic Chemistry
Division of Organic Chemistry and Biochemistry
Ruder Boskovic Institute, Zagreb (Croatia)
¯
ˇ
´
A. D. Katsenis
Laboratory of Inorganic Chemistry, Department of Chemistry
National and Kapodistrian University of Athens (Greece)
[**] We acknowledge the NSERC Discovery Grant, FRQNT Nouveaux
Chercheurs fund, Canada Foundation for Innovation Leader’s
Opportunity Fund (CFI-LOF), Tak-Hang (Bill) and Christina Chang
Fellowship in Chemistry (C.M.), and NSERC CREATE in Green
Chemistry for funding. Prof. D. S. Bohle is acknowledged for help
with single-crystal X-ray diffraction, and Dr. A. Wahba for MS data.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201404120.
Angew. Chem. Int. Ed. 2014, 53, 9321 –9324
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
9321

.
Angewandte
Communications
Table 1: Catalyst-free coupling of 1 with carbodiimides.[a]
conversion to 2a after 2 hours of neat milling, while 2 hours of
LAG, using nitromethane (h = 0.25 mLmgÀ1),[20] gave 2a in
98% yield (Scheme 1d). The product was isolated by a simple
protocol[19] in which the crude reaction mixture is briefly
(5 min) milled with aqueous sodium ethylenediaminetetra-
acetate to quench the reaction and remove the metal catalyst
by complexation. The water-insoluble 2a is isolated as a white
solid by filtration. That 2a forms mechanochemically rather
than during work-up is evidenced by Fourier-transform
attenuated total reflectance (FTIR-ATR) spectra (Fig-
ure 1a), which revealed the absence of the carbodiimide
band at 2120 cmÀ1 in the freshly milled reaction. If the milling
was performed without CuCl, the carbodiimide signal was
clearly visible, thus confirming that the reaction requires the
copper additive. Formation of 2a was confirmed by X-ray
crystallography using single crystals grown after work-up (see
the Supporting Information).
We also attempted the copper-catalyzed synthesis of 2a in
CH2Cl2 or acetone solution. After an overnight reflux no trace
of 2a was detected and the reactant 2 was retrieved, thus
highlighting the importance of milling for the copper-cata-
lyzed coupling. The inability to reproduce this catalytic
coupling in solution provided an opportunity to explore
a novel reaction using mechanochemistry only. We first
compared it to the recently reported[16] catalyst-free coupling
of 1 with DCC and DIC. We readily conducted both of these
reactions by neat milling and by LAG (Table 1).
[a] For reaction conditions please see the Supporting Information. The
yields reported are those of the isolated product. [b] Synthesis of 1 f was
only possible with 10 mol% CuCl.
Table 2: CuCl-catalyzed coupling of p-tolyl- (2) and p-chlorophenylsul-
fonamide (3) with different carbodiimides.[a]
Different carbodiimides were used to compare CuCl-
catalyzed mechanochemical coupling of 2 to that of the
catalyst-free coupling of 1. The latter readily reacted with all
explored carbodiimides except di(trimethylsilyl)carbodiimide
(Table 1) and the aromatic di(p-tolyl)carbodiimide (DPTC).
In contrast, CuCl-catalyzed coupling of 2 readily proceeded
with DCC, DIC, and DPTC (2a–c), but not with sterically
hindered carbodiimides involving tert-butyl and trimethylsilyl
groups (Table 2). An identical pattern of reactivity was
observed for p-chlorophenylsulfonamide (3), which exhibited
no reactivity on its own, but with CuCl readily yielded the N-
sulfonylguanidines 3a–c by using DCC, DIC, and DPTC
(Table 2).
[a] For reaction conditions please see the Supporting Information. The
yields reported are those of the isolated product. [b] Used 10 mol%
CuCl. [c] The reaction did not proceed even if the sulfonamide was first
milled with K2CO3.
These comparisons confirm that 1 is unique in its ability to
directly react with carbodiimides and suggest its reactivity is
limited to aliphatic substrates. In contrast, the CuCl-catalyzed
coupling is general with respect to the sulfonamide and
tolerates aromatic carbodiimides. Indeed, 10 mol% of CuCl
also enabled the coupling of 1 with DPTC, which was
Figure 1. FTIR-ATR spectra for mechanosynthesis of 2a: DCC (top);
freshly milled mixture of DCC and 2 with 5 mol% CuCl (middle), and
without CuCl (bottom).
9322
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 9321 –9324

Angewandte
Chemie
previously not achievable in solution or mechanochemically
(Table 1).[16] To verify the importance of CuCl in enabling the
coupling of aromatic carbodiimides, we explored the reaction
of 1 with di(o-tolyl)carbodiimide (DOTC). While the reaction
did not take place without CuCl, milling with 5 mol% CuCl
gave 73% conversion into the N-sulfonylguanidine as evi-
denced by 1H NMR and MS data (see the Supporting
Information).
Next, we explored the applicability of the mechanochem-
ical copper-catalyzed coupling to other commercially avail-
able arylsulfonamides (Table 3). No reactivity was observed
without CuCl. With CuCl, reactions readily took place in
almost all cases, thus providing N-sulfonylguanidines in
excellent yields after simple optimization. Select products
were characterized by X-ray crystallography (see the Sup-
porting Information). We also attempted syntheses of 3b, 4c,
and 6b in solution. After 18 hours at reflux in acetone, using
10 mol% CuCl, the conversion into 3b and 6b was 8% and
5%, respectively, whereas no conversion was observed for 4c.
The 2-naphthyl- (5) and p-nitrophenylsulfonamide (7)
exhibited poorer mechanochemical reactivity than other
tested sulfonamides (Table 3). In principle, LAG should
allow the optimization of mechanochemical reactions by
switching the catalytic liquid[21] in a similar way that solvent
switching can affect solution synthesis. To investigate how
a poorly behaving LAG coupling can be optimized, we
focused on the reaction of 5 with DCC and explored
increasing the catalyst amount, reaction time, and different
liquid additives at h = 0.25 mLmgÀ1 (Table 4). Quantitative
1
conversion (from H NMR and FTIR-ATR data) and 92%
yield of 5a were obtained using acetone as a grinding liquid
with 10 mol% CuCl (Tables 3 and 4).
Table 4: Optimization of copper-catalyzed LAG synthesis of 5a.
Entry CuCl (mol%) t [h] LAG
Conv. [%][a]
1
2
3
4
5
6
7
8
5
2
2
4
2
2
4
2
2
2
2
2
CH3NO2
CH3NO2
CH3NO2
CH3NO2
acetone
acetone
2-butanone
acetonitrile
cyclohexanone
N,N-dimethylformamide
neat
36
55
75
50
84
10
10
20
20
10
10
10
10
10
10
>95[b]
79
43
61
47
58
Table 3: Mechanochemical CuCl-catalyzed coupling of different com-
9
10
11
mercially available arylsulfonamides with DCC, DIC, and DPTC.[a]
[a] Based on 1H NMR spectroscopy. [b] Yield of the isolated product was
92%.
Syntheses of 3a and 3b were also conducted at 5 mmol
scale, thus yielding the expected products in 1.9 g (96%) and
1.5 g (87%) amounts, respectively, and demonstrating the
applicability of mechanochemical synthesis for gram-scale
reaction.
In conclusion, we used mechanochemistry to establish
a previously not known catalytic route[22] for one-step syn-
thesis of N-sulfonylguanidines from arylsulfonamides and
carbodiimides. This chemistry presents mechanosynthesis not
only as a tool for enhancing known procedures, but also as
a means to discover and develop synthetic pathways which are
difficult to access in solution. Attempts to conduct the
coupling reaction in solution have so far been either
unsuccessful or gave very poor conversions. This outcome
indicates that the sulfonamide–carbodiimide coupling is not
impossible in solution, but is greatly favored in a mechano-
chemical environment, possibly as a result of a higher
effective concentration of the catalyst in the absence of bulk
solvent. As the addition of a base did not induce catalyst-free
reactivity between sulfonamides and carbodiimides,[19] we
suggest that the role of CuCl might be largely in activating the
carbodiimide, for example, by coordinating to its p system.
We are now performing reaction screens and computational
studies to elucidate the mechanism of this and related[19,23]
mechanochemical coupling procedures.
[a] For reaction conditions please see the Supporting Information. The
yields reported are those of the isolated product. [b] Used 10% CuCl.
[c] Used 1.1 equiv carbodiimide. [d] Used 20% CuCl. [e] Optimized
reaction conditions: 10 mol% CuCl, acetone (h=0.25 mLmgÀ1), 4 h
milling.
Experimental Section
General Information: Syntheses of N-sulfonylguanidines were car-
ried out in a Retsch MM400 mill at a frequency of 30 Hz using
a 10 mL stainless steel milling jar and a single ball made of the same
Angew. Chem. Int. Ed. 2014, 53, 9321 –9324
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
9323

.
Angewandte
Communications
material (7 or 10 mm). Gram-scale reactions were carried out in
a 25 mL stainless steel milling jar. In a typical experiment, a mixture
of 0.50 mmol of sulfonamide, 0.50 mmol carbodiimide (1 equiv),
0.025–0.050 mmol (5–10% mol) of CuCl, and CH3NO2 as the grinding
liquid (h = 0.25 mLmgÀ1) was milled for 2 h. After the reaction, 3 mL
water and 20–40 mg of Na2H2EDTA·2H2O were added to the crude
reaction mixture, followed by 10 min of milling. The product was
separated by vacuum filtration and dried. For gram-scale syntheses,
5.0 mmol of sulfonamide, 5.0 mmol carbodiimide, 0.50 mmol CuCl
(10% mol) and CH3NO2 (h = 0.25 mLmgÀ1) were milled for 2 h, using
three 10 mm diameter balls in a 25 mL jar. After the reaction, 15 mL
of water and 400 mg of Na2H2EDTA·2H2O were added to the crude
reaction mixture, which was then milled for 10 min. The product was
separated by vacuum filtration and dried. Details of all experiments,
1H,13C NMR spectroscopy, and MS, TGA/DSC, and FTIR-ATR data
are given in the Supporting Information. CCDC 995641 (2a), 995642
(3b), 995643 (4a), 995644 (5b) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.
[6] a) C. B. Aakerçy, P. D. Chopade, Org. Lett. 2011, 13, 1; b) C. B.
Aakerçy, A. S. Sinha, K. N. Epa, C. L. Spartz, J. Desper, Chem.
ˇ
Commun. 2012, 48, 11289; c) V. Strukil, M. D. Igrc, M. Eckert-
ˇˇ ´
´
Maksic, T. Friscic, Chem. Eur. J. 2012, 18, 8464.
ˇ
´
´
[7] a) V. Strukil, D. Margetic, M. D. Igrc, M. Eckert-Maksic, T.
ˇˇ ´
Friscic, Chem. Commun. 2012, 48, 9705; b) M. Ferguson, N. Giri,
X. Huang, D. Apperley, S. L. James, Green Chem. 2014, 16, 1374.
[8] a) M. Pascu, A. Ruggi, R. Scopelliti, K. Severin, Chem.
Commun. 2013, 49, 45; b) V. P. Balema, J. W. Wiench, M.
Pruski, V. K. Pecharski, J. Am. Chem. Soc. 2002, 124, 6244.
[9] a) B. IÅli, N. Christinat, J. Tçnneman, C. Schꢅttler, R. Scopelliti,
K. Severin, J. Am. Chem. Soc. 2009, 131, 3154; b) Z. Zhang, G.-
W. Wang, C.-B. Miao, Y.-W. Dong, Y.-B. Shen, Chem. Commun.
2004, 16, 1832; c) Y.-W. Dong, G.-W. Wang, L. Wang, Tetrahe-
dron 2008, 64, 10148.
[10] J. Bonnamour, T.-X. Mꢂtro, J. Martinez, F. Lamaty, Green Chem.
2013, 15, 1116.
[11] a) P. J. Dunn, Chem. Soc. Rev. 2012, 41, 1452; b) C. Jimꢂnez-
Gonzꢀlez, D. J. C. Constable, C. S. Ponder, Chem. Soc. Rev. 2012,
41, 1485; c) H.-J. Federsel, Green Chem. 2013, 15, 3105.
[12] a) F. Li, G.-W. Wang, Chem. Soc. Rev. 2013, 42, 7535; b) G.-W.
Wang, K. Komatsu, Y. Murata, M. Shiro, Nature 1997, 387, 583.
[13] S. Tsuji, S. Kawano, M. Tsujii, N. Kawai, E. S. Gunawan, W. H.
Sun, M. Hori, Arzneim.-Forsch. 2001, 51, 46.
Received: April 8, 2014
Published online: July 7, 2014
[14] a) J. H. M. Lange, H. K. A. C. Coolen, H. H. van Stuivenberg,
J. A. R. Dijksman, A. H. J. Herremans, E. Ronken, H. G. Keizer,
K. Tipker, A. C. McCreary, W. Veerman, H. C. Wals, B. Stork,
P. C. Verveer, A. P. den Hartog, N. M. J. de Jong, T. J. P. Adolfs,
J. Hoogendoorn, C. G. Kruse, J. Med. Chem. 2004, 47, 627; b) P.
Deprez, J.-P. Vevert, Synth. Commun. 1996, 26, 4299; c) C.
Worch, C. Bolm, Synthesis 2007, 1355.
[15] a) K. Shiokawa, M. Koichi, T. Goto, A. Kamochi, S. Kohama,
United States Patent USP No. 4559079, 1985; b) M. A. Gonza-
lez, D. B. Gorman, C. T. Hamilton, G. A. Roth, Org. Process Res.
Dev. 2008, 12, 301; c) K. Shiokawa, M. Koichi, T. Goto, A.
Kamochi, S. Kohama, United States Patent USP No. 4619688,
1986.
À
Keywords: C N coupling · copper · heterogeneous catalysis ·
mechanosynthesis · synthetic methods
.
[1] a) S. L. James, C. J. Adams, C. Bolm, D. Braga, P. Collier, T.
ˇˇ ´
Friscic, F. Grepioni, K. D. M. Harris, G. Hyett, W. Jones, A.
Krebs, J. Mack, L. Maini, A. G. Orpen, I. P. Parkin, W. C.
Shearouse, J. W. Steed, D. C. Waddell, Chem. Soc. Rev. 2012, 41,
413; b) A. Bruckmann, A. Krebs, C. Bolm, Green Chem. 2008,
10, 1131; c) A. Stolle, T. Szuppa, S. E. S. Leonhardt, B.
Ondruschka, Chem. Soc. Rev. 2011, 40, 2317; d) G.-W. Wang,
Chem. Soc. Rev. 2013, 42, 7668; e) E. Boldyreva, Chem. Soc. Rev.
2013, 42, 7719; f) J. G. Hernꢀndez, E. Juaristi, Chem. Commun.
2012, 48, 5396; g) B. Rodrꢁguez, T. Rantanen, C. Bolm, Angew.
Chem. 2006, 118, 7078; Angew. Chem. Int. Ed. 2006, 45, 6924;
h) B. Rodrꢁguez, A. Bruckmann, C. Bolm, Chem. Eur. J. 2007, 13,
4710; i) Y.-F. Wang, R.-X. Chen, K. Wang, B.-B. Zhang, Z.-B. Li,
D.-Q. Xu, Green Chem. 2012, 14, 893; j) T. L. Cook, J. A. Walker,
J. Mack, Green Chem. 2013, 15, 617; k) R. Thorwirth, A. Stolle,
B. Ondruschka, Green Chem. 2010, 12, 985; l) D. A. Fulmer,
W. C. Shearouse, S. T. Medonza, J. Mack, Green Chem. 2009, 11,
1821; m) R. Thorwirth, A. Stolle, B. Ondruschka, A. Wild, U. S.
Schubert, Chem. Commun. 2011, 47, 4370; n) G.-W. Wang, Y.-W.
Dong, T.-T. Yuan, Y.-B. Shen, J. Org. Chem. 2008, 73, 7088; o) P.
Nun, V. Pꢂrez, M. Calmꢃs, J. Martinez, F. Lamaty, Chem. Eur. J.
2012, 18, 3773; p) V. Declerck, E. Colacino, X. Bantreil, J.
Martinez, F. Lamaty, Chem. Commun. 2012, 48, 11778; q) J. G.
Hernꢀndez, E. Juaristi, J. Org. Chem. 2011, 76, 1464; r) J. G.
Hernꢀndez, V. Garcꢁa-Lꢄpez, E. Juaristi, Tetrahedron 2012, 68,
92.
[16] a) B. A. Shainyan, L. L. Tolstikova, U. Schilde, J. Fluorine Chem.
2012, 135, 261; b) L. L. Tolstikova, N. N. Chipanina, L. P.
Oznobikhina, B. A. Shainyan, Russ. J. Org. Chem. 2011, 47, 1278.
[17] a) J. H. M. Lange, S. Verhoog, H. J. Sanders, A. Loevezijn, C. G.
Kruse, Tetrahedron Lett. 2011, 51, 3198; b) Y. Shi, J. Zhang,
Tetrahedron Lett. 2000, 41, 8075; c) S. Benvenuti, F. Severi, G.
Vampa, L. Malmusi, J. Heterocycl. Chem. 1995, 32, 1613.
[18] M. Gerlach, United States Patent USP No. 7671074 B2, 2010.
ˇ
ˇˇ ´
[19] D. Tan, V. Strukil, C. Mottillo, T. Friscic, Chem. Commun. 2014,
50, 5248.
[20] h is the ratio of added liquid (in mL) to the mass of reactants (in
mg), typically between 0.1–1 mLmgÀ1; a) The herein reported
reactions use 50 mL per 0.2 g of reactants (h = 0.25 mLmgÀ1).
ˇˇ ´
[21] a) T. Friscic, W. Jones, Cryst. Growth Des. 2009, 9, 1621; b) G. A.
Bowmaker, Chem. Commun. 2013, 49, 334.
À
[22] For recent reviews of metal-catalyzed C N coupling reactions:
a) J. Bariwal, E. van der Eycken, Chem. Soc. Rev. 2013, 42, 9283;
b) F. Monnier, M. Taillefer, Angew. Chem. 2009, 121, 7088;
Angew. Chem. Int. Ed. 2009, 48, 6954; c) J. F. Hartwig, Acc.
Chem. Res. 2008, 41, 1534; d) I. P. Beletskaya, A. V. Cheprakov,
Organometallics 2012, 31, 7753; e) P. S. Hanley, J. F. Hartwig,
Angew. Chem. 2013, 125, 8668; Angew. Chem. Int. Ed. 2013, 52,
8510; f) G. O. Jones, P. Liu, K. N. Houk, S. L. Buchwald, J. Am.
Chem. Soc. 2010, 132, 6205.
[2] a) F. Schneider, T. Szuppa, A. Stolle, B. Ondruschka, H. Hopf,
Green Chem. 2009, 11, 1894; b) R. B. N. Baig, R. S. Varma,
Chem. Soc. Rev. 2012, 41, 1559.
ˇˇ ´
[3] a) T. Friscic, S. L. Childs, S. A. A. Rizvi, W. Jones, CrystEng-
ˇˇ ´
Comm 2009, 11, 418; b) T. Friscic, Chem. Soc. Rev. 2012, 41,
3493.
[4] a) R. Schmidt, A. Stolle, B. Ondruschka, Green Chem. 2012, 14,
1673; b) G. Kaupp, M. R. Naimi-Jamal, V. Stepanenko, Chem.
Eur. J. 2003, 9, 4156.
[23] While the exceptional reactivity of
1 has not yet been
explained,[16] a search of the Cambridge Structural Database
À
(V5.34) shows that it exhibits an unusually short S N bond
ˇ
[5] a) V. Strukil, L. Fꢀbiꢀn, D. G. Reid, M. J. Duer, G. J. Jackson, M.
(1.55–1.57 ꢆ) compared to other sulfonamides in our study
(1.59–1.62 ꢆ).
´
ˇˇ ´
Eckert-Maksic, T. Friscic, Chem. Commun. 2010, 46, 9191;
b) G. A. Bowmaker, N. Chaichit, C. Pakawatchai, B. W. Skelton,
A. H. White, Dalton Trans. 2008, 2926.
9324 www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 9321 –9324