Notes and references
1 (a) J. Fraxedas, Molecular Organic Materials: From Molecules to
Crystalline Solids, Cambridge University Press, Cambridge, 2006;
(b) A. Kleeman and J. Engel, Pharmaceutical Substances: Syntheses,
Patents, Applications, Thieme, Stuttgart, 4th edn, 2001; (c) J. M.
Humphrey and A. R. Chamberlin, Chem. Rev., 1997, 97, 2243.
2 (a) C. A. G. N. Montalbetti and V. Falque, Tetrahedron, 2005, 61,
10827; (b) R. C. Larock, Comprehensive Organic Transformations,
Wiley-VCH, Weinheim, 1999; (c) P. D. Bailey, I. D. Collier and
K. M. Morgan, in Comprehensive Organic Functional Group
Transformations, ed. A. R. Katritzky, O. Meth-Cohn and
C. W. Rees, Pergamon, Cambridge, 1995, ch. 6, vol. 5.
3 Selected recent examples: (a) J. Li, F. Xu, Y. Zhang and Q. Shen,
J. Org. Chem., 2009, 74, 2575; (b) F. Wang, H. Liu, H. Fu, Y. Jiang
and Y. Zhao, Adv. Synth. Catal., 2009, 351, 246;
(c) L. U. Nordstrøm, H. Vogt and R. Madsen, J. Am. Chem.
Soc., 2008, 130, 17672; (d) L. Wang, H. Fu, Y. Jiang and
Y. Zhao, Chem.–Eur. J., 2008, 14, 10722; (e) K. R. Reddy,
C. U. Maheswari, M. Venkateshwar and M. L. Kantam, Eur. J.
Org. Chem., 2008, 3619; (f) C. Fang, W. Qian and W. Bao, Synlett,
2008, 2529; (g) J. Chan, K. D. Baucom and J. A. Murry, J. Am.
Chem. Soc., 2007, 129, 14106; (h) J. W. Bode and S. S. Sohn, J. Am.
Chem. Soc., 2007, 129, 13798; (i) H. U. Vora and T. Rovis,
J. Am. Chem. Soc., 2007, 129, 13796; (j) K. Ekoue-Kovi and
C. Wolf, Org. Lett., 2007, 9, 3429; (k) C. Gunanathan, Y.
Ben-David and D. Milstein, Science, 2007, 317, 790.
Fig.
3 Tentative mechanism for Cu(I)-catalysed amidation of
aldehydes with TsNQIPh.
The beneficial effect of added pyridine led us to consider the
possibility that N-tosyliminopyridine 5 shown in Fig. 2 was an
intermediate nitrene transfer agent.12 Once again, we were able
to prepare an authentic sample of 5 and demonstrate that it
was not competent as a nitrene source under our reaction
conditions. Nor could 5 be observed when pyridine, TsNQIPh
and CuI were combined in the absence of aldehyde. We
therefore assume that the role of pyridine is as a ligand.
Given that direct reaction of an in situ formed copper
nitrenoid species with the aldehyde appeared likely, we
speculated that this occurred via rate determining insertion
into the aldehyde C–H bond. This mechanism predicts deuterium
incorporation into the amide product, that is formation of
RCONDTs. Indeed, this was observed with the ruthenium-
catalysed version of the reaction we communicated earlier.4
Reaction of benzaldehyde-a-d1 with TsNQIPh, copper(I)
iodide and pyridine under standard conditions led to 56%
deuterium incorporation (cf. 76% with ruthenium).4
We therefore proceeded to measure the deuterium kinetic
isotope effect for this reaction with 1b and benzaldehyde-d6
as the test substrates. Analysis by LCMS gave a kH/kD
value of 3.8. This is clearly indicative of rate determining
carbon–hydrogen bond cleavage. The value of 3.8 is similar to
that we reported for copper catalysed nitrenoid insertion into
dibenzyl ether,7 which we explained by an asynchronous
concerted mechanism13 shown in Fig. 3. If this is the case, the
transition state could resemble that depicted in Fig. 3 where
N–H bond formation is further advanced than C–N bond
formation.
4 J. W. W. Chang and P. W. H. Chan, Angew. Chem., Int. Ed., 2008,
47, 1138, and references therein.
5 (a) F. Collet, R. H. Dodd and P. Dauban, Chem. Commun., 2009,
5061; (b) S. Fantauzzi, A. Caselli and E. Gallo, Dalton Trans.,
2009, 5434; (c) M. M. Dıaz-Requejo and P. J. Perez, Chem. Rev.,
2008, 108, 3379; (d) H. M. L. Davies and J. R. Manning, Nature,
2008, 451, 417; (e) H. M. L. Davies, Angew. Chem., Int. Ed., 2006,
45, 6422; (f) Z. Li and C. He, Eur. J. Org. Chem., 2006, 4313;
(g) A. R. Dick and M. S. Sanford, Tetrahedron, 2006, 62, 2439;
(h) H. Lebel, O. Leogane, K. Huard and S. Lectard, Pure Appl.
Chem., 2006, 78, 363; (i) C. G. Espino and J. Du Bois, in
Modern Rhodium-Catalyzed Organic Reactions, ed. P. A. Evans,
Wiley-VCH, Weinheim, 2005, p. 379; (j) H. M. L. Davies and
M. S. Long, Angew. Chem., Int. Ed., 2005, 44, 3518; (k) P. Muller
and C. Fruit, Chem. Rev., 2003, 103, 2905.
6 Selected recent examples using TsNQIPh: (a) J. W. W. Chang,
T. M. U. Ton, Z. Zhang, Y. Xu and P. W. H. Chan, Tetrahedron
Lett., 2009, 50, 161, and references therein; (b) H. Han, S. B. Park,
S. K. Kim and S. Chang, J. Org. Chem., 2008, 73, 2862; (c) Q. Xu
and D. H. Appella, Org. Lett., 2008, 10, 1497; (d) H. Lebel,
S. Lectard and M. Parmentier, Org. Lett., 2007, 9, 4797;
(e) R. Liu, S. R. Herron and S. A. Fleming, J. Org. Chem., 2007,
72, 5587; (f) M. Fructos, S. Trofimenko, M. M. Dıaz-Requejo and
P. J. Perez, J. Am. Chem. Soc., 2006, 128, 11784.
In conclusion, we have developed
a straightforward
7 D. P. Albone, S. Challenger, A. M. Derrick, S. M. Fillery,
J. L. Irwin, C. M. Parsons, H. Takada, P. C. Taylor and
D. J. Wilson, Org. Biomol. Chem., 2005, 3, 107.
procedure for the amidation of a wide range of aldehydes.
The catalysts are inexpensive and extremely simple to form
in situ from copper(I) halides and pyridine. The reaction
appears to proceed by rate determining insertion of a
copper–nitrenoid species into the carbon–hydrogen bond of
the aldehyde. For the synthesis of N-acylsulfonamides 2, the
new procedure should be considered as highly practical.
Additionally, the free amide adduct can be accessed via a
simple tosyl deprotection step, for example, with Mg powder
in MeOH at room temperature. Extension of the method to
other nitrogen substitutents is the subject of the next stage of
our programme.
8 Selected examples using TsNClNaÁ3H2O: (a) R. Bhuyan and
K. M. Nicholas, Org. Lett., 2007, 9, 3957; (b) I. Cano,
M. C. Nicasio and P. J. Perez, Dalton Trans., 2009, 730;
(c) H. Martınez-Garcıa, D. Morales, J. Perez, D. J. Coady,
C. W. Bielawski, D. E. Gross, L. Cuesta, M. Marquez and
J. L. Sessler, Organometallics, 2007, 26, 6511, and references therein.
9 A. Armstrong and D. P. G. Emmerson, Org. Lett., 2009, 11, 1547,
and references therein.
10 In comparison, ruthenium(II) porphyrin catalysts are typically
preformed prior to use. Additionally, for the analogous ruthenium(II)
porphyrin-catalysed reactions of aromatic aldehydes with TsNQIPh,
removal of the metal catalyst was found to be non-trivial and required
careful separation by flash column chromatography. In this work,
removal of the copper catalyst was readily achieved by filtration
through Celites. Please refer to ESIw for further details.
We gratefully acknowledge a University Research Committee
Grant (RG55/06) from Nanyang Technological University
(NTU), the Singapore Millennium Foundation (SMF) for a
SMF PhD Scholarship award to J. W. W. C., and NTU for a
Nanyang President’s Graduate Scholarship award to T. M. U. T.
and an Undergraduate Research Experience on CAmpus
(URECA) stipend to S. T.
11 J. L. Garcıa-Ruano, J. Aleman, C. Fajardo and A. Parra,
Org. Lett., 2005, 7, 5493.
12 Y. Jiang, G.-C. Zhou, G.-L. He, L. He, J.-L. Li and S.-L. Zheng,
Synthesis, 2007, 1459.
13 See ref. 5 and K. W. Fiori, C. G. Espino, B. H. Brodsky and J. Du
Bois, Tetrahedron, 2009, 65, 3042, and references therein.
ꢀc
This journal is The Royal Society of Chemistry 2010
924 | Chem. Commun., 2010, 46, 922–924