COMMUNICATIONS
Amines vs. N-Oxides as Organocatalysts for Acylation, Sulfonylation
[17] M. R. Heinrich, H. S. Klisa, H. Mayr, W. Steglich, H.
Experimental Section
Zipse, Angew. Chem. 2003, 115, 4975–4977; Angew.
Chem. Int. Ed. 2003, 42, 4826–4828.
[18] P. Patschinski, C. Zhang, H. Zipse, J. Org. Chem. 2014,
79, 8348–8357.
General Procedure for Synthesis of TES Ethers of
tert-Alcohols
To a solution of the alcohol component (1.75 mmol), 1-
methylimidazole N-oxide (8, 4.3 mg, 2.5 mol%) in CHCl3
(8.75 mL, 0.2M) was added PMP (0.63 mL, 3.50 mmol) fol-
lowed by TES-Cl (0.367 mL, 2.19 mmol). The reaction mix-
ture was then heated to 408C for 8 h before the addition of
MeOH (1 mL) to quench the reaction. The resulting solu-
tion was concentrated under vacuum and the residue puri-
fied by flash chromatography to afford the product; yield:
87–98%.
[19] J. I. Murray, R. Woscholski, A. C. Spivey, Synlett 2015,
985–990.
[20] J. I. Murray, R. Woscholski, A. C. Spivey, Chem.
Commun. 2014, 50, 13608–13611.
[21] 4-DMAP N-oxide has recently been shown to be an ef-
ficient catalyst for TBDPS protection of sec-alcohols:
K. Yoshida, K. Takao, Tetrahedron Lett. 2014, 55, 6861–
6863.
[22] G. Laus, A. Schwärzler, G. Bentivoglio, M. Hummel, V.
Kahlenberg, K. Wurst, E. Kristeva, J. Schütz, H. Ko-
packa, C. Kreutz, G. Bonn, Y. Andriyko, G. Nauer, H.
Schottenberger, Z. Naturforsch. Sect. B 2008, 63, 447–
464.
Acknowledgements
[23] NMI-O was reported to be an efficient catalyst for cer-
tain Morita-Baylis–Hillman reactions: Y.-S. Lin, C.-W.
Liu, T. Y. R. Tsai, Tetrahedron Lett. 2005, 46, 1859–
1861. However, these authors were subsquently shown
by Laus et al. to have mistakenly employed NMI semi-
We thank the EPSRC, the Institute of Chemical Biology
(ICB, Imperial College London) and the SCI (Messel Schol-
arship, JIM) for funding.
perhydrate [NMI·1= H2O2] for these studies (see ref.[22]).
2
The error resulted from the use of H2O2 for the direct
oxidation of NMI; direct oxidation of NMI to NMI-O,
using various oxidants, has been repeatedly reported
not to provide NMI-O (see Pevzner et al., ref.[24]). We
have also found that direct oxidation of NMI does not
furnish NMI-O; it is likely that NMI-O is concomitant-
ly deoxygenated by hydrogen peroxide and by peracids
(see Vedsø et al., ref.[25]).
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