ORGANIC
LETTERS
2007
Vol. 9, No. 10
1859-1862
Mild and Efficient
Pentafluorophenylammonium Triflate
(PFPAT)-Catalyzed C-Acylations of Enol
Silyl Ethers or Ketene Silyl (Thio)Acetals
with Acid Chlorides
Akira Iida, Jun Osada, Ryohei Nagase, Tomonori Misaki, and Yoo Tanabe*
Department of Chemistry, School of Science and Technology, Kwansei Gakuin
UniVersity, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan
Received January 25, 2007
ABSTRACT
A pentafluorophenylammonium triflate (PFPAT) catalyst (5 mol %) successfully promoted C-acylation of enol silyl ethers with acid chloride to
produce various -diketones (12 examples; 62 92% yield). Similarly, C-acylation of ketene silyl acetals or ketene silyl thioacetals (i.e., crossed
Claisen condensation) proceeded smoothly to provide not only -monoalkylated -keto (thio)esters but also thermodynamically unfavorable
(less accessible) -dialkylated -keto (thio)esters in good to excellent yield (38 examples; 60 92% yield).
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Regio- and chemoselective C-acylation of the R-position of
carbonyl compounds is recognized as a fundamental and
useful C-C bond forming reaction for obtaining 1,3-
dicarbonyl compounds in organic syntheses.1 There are a
number of useful catalytic carbon-carbon bond forming
reactions using enol silyl ethers, ketene silyl acetals (KSAs),
and ketene silyl thioacetals (KSTAs), such as the aldol,2
Mannich,3 Michael,4 and Diels-Alder reactions.5 In contrast,
(2) (a) Mukaiyama, T.; Narasaka, K.; Banno, K. Chem. Lett. 1973, 1011.
(b) Mukaiyama, T.; Narasaka, K.; Banno, K. J. Am. Chem. Soc. 1974, 96,
7503. (c) Langer, P.; Koehler, V. Org. Lett. 2000, 2, 1597. (d) Matsukawa,
S.; Okano, N.; Imamoto, T. Tetrahedron Lett. 2000, 41, 103. (e) Delas, C.;
Blacque, O.; Moise, C. Tetrahedron Lett. 2000, 41, 8269. (f) Ishihara, K.;
Kondo, S.; Yamamoto, H. J. Org. Chem. 2000, 65, 9125. (g) Kumareswaran,
R.; Reddy, B. G.; Vankar, Y. D. Tetrahedron Lett. 2000, 41, 8269. (h)
Armstrong, A.; Critchley, T. J.; Gourdel-Martin, M.-E.; Kelsey, R. D.;
Mortlock, A. A. J. Chem. Soc., Perkin Trans. 1 2002, 1344. (i) Cle´zio, I.
L.; Escudier, J.-M.; Vigroux, A. Org. Lett. 2003, 5, 161. (j) Ishihara, K.;
Yamamoto, H. Boron and Silicon Lewis Acids for Mukaiyama Aldol
Reactions. In Modern Aldol Reactions; Mahrwald, R., Ed.; 2004; p 25. (k)
Mukaiyama, T. Angew. Chem., Int. Ed. 2004, 43, 5590. (l) Li, H.-J.; Tian,
H.-Y.; Wu, Y.-C.; Chen, Y.-J.; Liu, L.; Wang, D.; Li, C.-J. AdV. Synth.
Catal. 2005, 347, 1247. (m) Adhikari, S.; Caille, S.; Hanbauer, M.; Ngo,
V. X.; Overman, L. E. Org. Lett. 2005, 7, 2795. (n) Acocella, M. R.; Massa,
A.; Palombi, L.; Villano, R.; Scettri, A. Tetrahedron Lett. 2005, 46, 6141.
(1) (a) For examples, see: Smith, M. B.; March, J. AdVanced Organic
Chemistry, 5th ed.; John Wiley: New York, 2001; p 569. (b) Vollhardt, K.
P. C.; Schore, N. E. Organic Chemistry, 3rd ed.; Freeman: New York,
1999; p 1039. (c) Clayden, J.; Greeves, N.; Warren, S.; Wothers, P. Organic
Chemistry; Oxford: New York, 2001; p 726. (d) Ku¨rti, L.; Czako´, B.
Strategic Applications of Named Reactions in Organic Synthesis; Elsevier:
Burlington, 2005; p 86 and p 138. (e) Manyik, R. M.; Frostick, F. C.;
Sanderson, J. J.; Hauser, C. R. J. Am. Chem. Soc. 1953, 75, 5030. (f) Mao,
C. L.; Frostick, F. C.; Man, E. H.; Manyik, R. M.; Wells, R. L.; Hauser, C.
R. J. Org. Chem. 1969, 34, 1425. (g) House, H.; Auerbach, R. A.; Gall,
M.; Peet, N. P. J. Org. Chem. 1973, 38, 514. (h) Beck, A. K.; Hoekstra, M.
S.; Seebach, D. Tetrahedron Lett. 1977, 13, 1187. (i) Howard, A. S.;
Meerholz, C. A.; Michael, J. P. Tetrahedron Lett. 1979, 15, 1339. (j)
Fleming, I.; Iqbal, J.; Krebs, E.-P. Tetrahedron 1983, 39, 841. (k) Stefaniak,
M. H. Synlett 1997, 677.
10.1021/ol070191b CCC: $37.00
© 2007 American Chemical Society
Published on Web 04/13/2007