Angewandte
Chemie
yields (Scheme 3). Second, it was shown that polyfluoro-
phenyl oxiranes are excellent substrates for SNAr reactions[9]
(Scheme 4). Thus, 2l underwent an efficient substitution
reaction with piperidine and sodium methylthiolate to
produce the corresponding N- and S-containing products 5a
and 5b, respectively, in excellent yields and with no oxirane
ring-opening[10] products detected.
[1] a) H.-J. Frohn, H. Franke, P. Fritzen, V. V. Bardin, J. Organomet.
emann, B. M. Kariuki, R. Van Deun, Z. Pikramenou, Chem. Eur.
f) A. M. Trzeciak, H. Bartosz-Bechowski, Z. Ciunik, K. Niesyty,
(Albemarle Corporation (Richmond, VA) USA), U. S. Patent
6248265 B1, Jan. 2, 2001.
[2] For examples on preparation of pentafluorophenyl lithium and
PFPBr by oxidative addition with transition metals, see: e) B. B.
Anderson, C. L. Behrens, L. J. Radonovich, K. J. Klabunde, J.
Martin-Ruiz, D. Milstein, J. Am. Chem. Soc. 2001, 123, 11504;
Ivushkin, P. K. Sazonov, G. A. Artamkina, I. P. Beletskaya, J.
of PFP anion through electrophilic bromine abstraction by
phosphines, see: j) V. V. Bardin, L. S. Pressman, L. N. Rogoza,
Scheme 3. Semipinacol rearrangement of oxiranes.
Scheme 4. SNAr on a pentafluorophenyl ring.
In conclusion, we have demonstrated that amphoteric
bromopolyfluoroarenes (or heteroarenes) can serve as equiv-
alents of both Br+ and aryl (or hetaryl) anions in the same
cascade transformation. The reaction of enolizable ketones
with bromopolyfluoroarenes leads to a variety of valuable tri-
and tetrasubstituted epoxides[11] in good to excellent yields
and diastereoselectivities. The synthetic utility of the poly-
fluorophenyl-containing oxirane products was demonstrated
by their further transformation, including a semi-pinacol
rearrangement and SNAr reactions.
[3] For examples of electrophilic bromine abstraction, see: a) L. R.
Falvello, J. Fornies, R. Navarro, A. Rueda, E. P. Urriolabeitia,
[6] For an example of electrophilic iodine abstraction from per-
fluoroalkyl iodides, see: J. L. Howell, B. J. Muzzi, N. L. Rider,
Alesi, E. Emer, M. G. Capdevila, D. Petruzziello, A. Gualandi,
Experimental Section
Ketone (0.5 mmol) was added to an oven-dried, conical vial equipped
with a magnetic stir bar and a PTFE-topped screw cap. The vessel was
then evacuated and recharged three times with argon. Anhydrous 1,4-
dioxane (2.5 mL) was added dropwise and the reaction mixture was
stirred until the ketone was completely dissolved. NaHMDS (0.6 mL,
1m in THF) was subsequently added to the solution and the resulting
mixture was stirred for 5 min. PFPBr, or another aryl bromide, was
then added dropwise to this mixture and stirred for another 15 min, at
which time precipitation of NaBr was observed. The reaction mixture
was filtered through a silica or zeolite pad and washed with 50 mL of
diethyl ether. The filtrate was concentrated under reduced pressure
and the residue was purified by column chromatography on silica gel
with a gradient from pure hexanes to 20:1 (v/v) hexanes/ethyl acetate
to obtain the final product.
[8] For examples of metal-catalyzed semipinacol rearrangements,
[9] For SNAr reactions on polyfluorophenyl rings, see: a) K. Tanaka,
T. Takeyama, R. Yukawa, S. Iwata, T. Kurushima, Supramol.
[10] For oxirane ring opening reactions with N- and S-nucleophiles,
see: a) S. Rodrꢃguez-Escrich, K. S. Reddy, C. Jimeno, G. Colet,
C. Rodrꢃguez-Escrich, L. Solꢄ, A. Vidal-Ferran, M. A. Pericꢄs, J.
Org. Chem. 2008, 73, 5340; b) D. Acetti, E. Brenna, C. Fuganti,
[11] For the synthetic use of oxiranes, see: a) D. M. Hodgson, C. D.
Bray in Aziridines and Epoxides in Organic Synthesis (Eds.:
A. K. Yudin), Wiley-VCH, Weinheim, 2006, pp. 169 – 170;
b) R. M. Hanson in Organic Reactions, Wiley, Hoboken, 2004,
pp. 116, 118; c) A. Nagaki, E. Takizawa, J. Yoshida, Chem. Eur. J.
Received: October 2, 2011
Published online: December 15, 2011
Keywords: bromopentafluorobenzene ·
.
cascade transformations · epoxidation ·
perfluorinated compounds · perfluoroarylepoxides
Angew. Chem. Int. Ed. 2012, 51, 1225 –1227
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1227