10.1002/anie.202107438
Angewandte Chemie International Edition
RESEARCH ARTICLE
[1]
[2]
[3]
[4]
G. M. Whitesides, Isr. J. Chem. 2018, 58, 142-150.
B. M. Trost, Science 1983, 219, 245-250.
I. S. Young, P. S. Baran, Nat. Chem. 2009, 1, 193-205.
J. Mahatthananchai, A. M. Dumas, J. W. Bode, Angew. Chem. Int. Ed. Engl. 2012, 51, 10954-10990; Angew. Chem. 2012, 124,
11114-11152.
[5]
[6]
[7]
T. Ohshima, T. Iwasaki, Y. Maegawa, A. Yoshiyama, K. Mashima, J. Am. Chem. Soc. 2008, 130, 2944-2945.
R. Horikawa, C. Fujimoto, R. Yazaki, T. Ohshima, Chem. Eur. J. 2016, 22, 12278-12281.
K. Sugahara, N. Satake, K. Kamata, T. Nakajima, N. Mizuno, Angew. Chem. Int. Ed. Engl. 2014, 53, 13248-13252; Angew. Chem.
2014, 126, 13464-13468.
[8]
[9]
M. Hatano, Y. Furuya, T. Shimmura, K. Moriyama, S. Kamiya, T. Maki, K. Ishihara, Org. Lett. 2011, 13, 426-429.
M. Hatano, K. Ishihara, ChemComm 2013, 49, 1983-1997.
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
Y. Hayashi, S. Santoro, Y. Azuma, F. Himo, T. Ohshima, K. Mashima, J. Am. Chem. Soc. 2013, 135, 6192-6199.
D. Nakatake, Y. Yokote, Y. Matsushima, R. Yazaki, T. Ohshima, Green Chem. 2016, 18, 1524-1530.
M. H. Lin, T. V. RajanBabu, Org. Lett. 2000, 2, 997-1000.
S. De Sarkar, S. Grimme, A. Studer, J. Am. Chem. Soc. 2010, 132, 1190-1191.
R. C. Samanta, S. De Sarkar, R. Fröhlich, S. Grimme, A. Studer, Chem. Sci. 2013, 4, 2177-2184.
L. Gardossi, D. Bianchi, A. M. Klibanov, J. Am. Chem.Soc. 1991, 113, 6328-6329.
R. N. Ram, V. K. Soni, D. K. Gupta, Tetrahedron 2012, 68, 9068-9075.
Y. M. Osornio, P. Uebelhart, S. Bosshard, F. Konrad, J. S. Siegel, E. M. Landau, J. Org. Chem. 2012, 77, 10583-10595.
S. B. Kang, E. J. Ahn, Y. Kim, Y. H. Kim, Tetrahedron Lett. 1996, 37, 9317-9320.
C. Larrivee-Aboussafy, B. P. Jones, K. E. Price, M. A. Hardink, R. W. McLaughlin, B. M. Lillie, J. M. Hawkins, R. Vaidyanathan,
Org. Lett. 2010, 12, 324-327.
[20]
[21]
[22]
W. R. Roush, S. Russo-Rodriguez, J. Org. Chem. 1985, 50, 3224-3226.
S. T. Heller, T. Fu, R. Sarpong, Org. Lett. 2012, 14, 1970-1973.
The pKa of 4-(dimethylamino)pyridinium cation is 18.0 in acetontrile, while that of triethylammonium cation is 18.8. (see reference
38)
[23]
[24]
Selectivity was determined by analysis of the 1H NMR spectrum of the crude product after extraction but prior to any other
purification protocols.
Byproduct imidazole undegoes an acid-base reaction with the pyridinium ion, generating imidazolium salts that typically precipitate
from the reaction mixture.
[25]
[26]
[27]
[28]
[29]
[30]
[31]
S. Ohta, A. Shimabayashi, M. Aono, M. Okamoto, Synthesis 1982, 1982, 833-834.
S. T. Heller, E. E. Schultz, R. Sarpong, Angew. Chem. Int. Ed. Engl. 2012, 51, 8304-8308; Angew. Chem. 2012, 124, 8429-8433.
The only variables adjusted from subtrate to substrate were reaction time and, in a few cases, the amount of DBU added.
In some cases 2-3% of what appeared to be bisacylated product was observed in crude NMR spectra of crude isolated product.
Typically, imidazole hydrochloride precipitates from the mixture as the reaction proceeds.
G. W. Anderson, R. Paul, J. Am. Chem. Soc. 1958, 80, 4423-4423.
The increased amount of pyridinium ion added in Method B accounts for the mole equivalent of imidazole—which scavenges the
pyridinium ion via acid-base reaction—generated from the consumption of CDI
[32]
[33]
H. A. Staab, Liebigs Ann. 1957, 609, 83-88.
pKa values measured in DMSO are strongly correlated with those in acetonitrile or DMF (B. G. Cox, Acids and Bases: Solvent
Effects on Acids-Base Strength, Oxford University Press, 2013 and S. T. Heller, T. P. Silverstein, ChemTexts 2020, 6); moreover,
pKas of many of the nucleophilic groups involved in this acylation (simple alcohols, anilines, indoles, and many phenols) are not
known in acetonitrile. These values as are both predictive for acid-base catalysis and strongly correlated with hydrogen-bond
strengths (P. Gilli, L. Pretto, V. Bertolasi, G. Gilli, Acc. Chem. Res. 2009, 42, 33-44.)
Aliphatic amines are an apparent exception to this trend, possibly because they are mostly protonated--and therefore non-
nucleophilic--in the presence of the pyridinium ion.
There is precedent for DBU to interact with the electrophilic species in an acylation as it has been implicated as a nucleophilic
catalyst (W. C. Shieh, S. Dell, O. Repic, J. Org. Chem. 2002, 67, 2188-2191); however, we do not think this mode of activation is
relevant for the DBU-catalyzed O-acylation described here. If DBU functioned as a nucleophilic catalyst toward N-acylimidazoles in
this reaction, it would be reasonable to assume the same role toward acid chlorides and anhydrides, all of which would yield the
same electrophilic N-acylguanidinium cation, and accordingly all give the same sense of selectivity. Yet acid chlorides and
anhydrides undergo selective N-acylation of anilines in the presence of DBU (Table 2, compare entries 2,4,and 7).
B. G. G. Lohmeijer, R. C. Pratt, F. Leibfarth, J. W. Logan, D. A. Long, A. P. Dove, F. Nederberg, J. Choi, C. Wade, R. M.
Waymouth, J. L. Hedrick, Macromolecules 2006, 39, 8574-8583.
[34]
[35]
[36]
[37]
[38]
J. C. Adrian, C. S. Wilcox, J. Am. Chem. Soc. 1989, 111, 8055-8057.
S. Tshepelevitsh, A. Kütt, M. Lõkov, I. Kaljurand, J. Saame, A. Heering, P. G. Plieger, R. Vianello, I. Leito, Eur. J. Org. Chem. 2019,
6735-6748.
[39]
[40]
[41]
[42]
W. N. Olmstead, Z. Margolin, F. G. Bordwell, J. Org. Chem. 1980, 45, 3295-3299.
X. Yang, V. B. Birman, Org. Lett. 2009, 11, 1499-1502.
S. T. Heller, R. Sarpong, Tetrahedron 2011, 67, 8851-8859.
H. Reich, " Hans Reich's Collection: Bordwell pKa Table", can be found under
https://organicchemistrydata.org/hansreich/resources/pka/" 2021.
[43]
These intermediates were somewhat longer lived than phenyl esters and could be directly observed even by qualitative techniques
such as TLC.
[44]
[45]
[46]
F. G. Bordwell, D. Algrim, N. R. Vanier, J. Org. Chem. 1977, 42, 1817-1819.
Essentially, some aliphatic amines.
F. G. Bordwell, G. E. Drucker, H. E. Fried, J. Org. Chem. 1981, 46, 632-635.
8
This article is protected by copyright. All rights reserved.