Organic Letters
Letter
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be a suitable approach whenever stable peroxy enolates are
involved in Weitz−Scheffer-type epoxidations.
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ASSOCIATED CONTENT
* Supporting Information
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X-ray data for compound 2f (CIF)
X-ray data for compound 3g (CIF)
Experimental details, analytical data, NMR spectra, HPLC
traces, optimized geometries, and computational details
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Chem., Int. Ed. 2017, 56, 5332.
(12) For a single example of optically active spiropyrazolone epoxide,
see: Rassu, G.; Zambrano, V.; Pinna, L.; Curti, C.; Battistini, L.; Sartori,
A.; Pelosi, G.; Casiraghi, G.; Zanardi, F. Adv. Synth. Catal. 2014, 356,
2330.
AUTHOR INFORMATION
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Corresponding Author
ORCID
Notes
(13) Kirschke, K.; Hubner, P.; Lutze, G.; Grundemann, E.; Ramm, M.;
̈
̈
Xue, F.; Bao, X.; Zou, L.; Qu, J.; Wang, B. Liebigs Ann. Chem. 1994, 1994,
159. For asymmetric synthesis of 4-hydroxypyrazolones, see: Xue, F.;
Bao, X.; Zou, L.; Qu, J.; Wang, B. Adv. Synth. Catal. 2016, 358, 3971.
(14) (a) Russo, A.; Galdi, G.; Croce, G.; Lattanzi, A. Chem. - Eur. J.
2012, 18, 6152. (b) Meninno, S.; Vidal-Albalat, A.; Lattanzi, A. Org. Lett.
2015, 17, 4348. (c) Meninno, S.; Zullo, L.; Overgaard, J.; Lattanzi, A.
Adv. Synth. Catal. 2017, 359, 913. (d) Kobayashi, Y.; Li, S.; Takemoto, Y.
Asian J. Org. Chem. 2014, 3, 403.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was supported by MIUR, University of Salerno,
POR Regione Campania FESR 2007-2013-O.O.2.1 (Farm-
aBioNet), the Danish National Research Foundation
(DNRF93), and CINECA (HP10CJSY9Q) for the availability
of high-performance computational resources. We thank Dr. P.
Iannece (University of Salerno) for assistance with MS spectra
analyses.
̂
(15) Ege, S. N.; Adams, A. D.; Gess, E. J.; Ragone, K. S.; Kober, B. J.;
Lampert, M. B. J. Chem. Soc., Perkin Trans. 1 1983, 1, 325.
(16) cis- and trans-epoxides were reported to occur from stereospecific
m-CPBA epoxidation of the E/Z-alkene mixture present in solution; see:
Lo Vecchio, G.; Gattuso, M.; Stagno d’Alcontres, G. Gazz. Chim. Ital.
1969, 99, 121.
(17) Weitz, E.; Scheffer, A. Ber. Dtsch. Chem. Ges. B 1921, 54, 2327.
(18) For reviews, see: (a) Schindler, C. S.; Jacobsen, E. N. Science 2013,
340, 1052. (b) Oliveira, M. T.; Luparia, M.; Audisio, D.; Maulide, N.
Angew. Chem., Int. Ed. 2013, 52, 13149. (c) Bihani, M.; Zhao, J. C.-G.
Adv. Synth. Catal. 2017, 359, 534. (d) Lin, L.; Feng, X. Chem. - Eur. J.
2017, 23, 6464.
(19) Meninno, S.; Croce, G.; Lattanzi, A. Org. Lett. 2013, 15, 3436.
(20) As a matter of comparison, the racemic epoxidation of
representative alkenes 1a,g performed at room temperature with the
NaOH/H2O2 system (ref 15) afforded the corresponding epoxides 2a,g
in 75−80% yield and 90:10−91:9 trans/cis ratio, respectively.
(22) The formation of the cis-epoxide might be explained by changed
sterics or/and electronic requirements achieved in the different TS
complex, leading to a more favorable ring closure of the first formed
adduct before the C−C bond rotation occurred. This outcome has been
frequently observed in stereoselective Weitz−Scheffer-type epoxida-
tions.
(23) Calculations were performed at the PCM (toluene) M06-2X/6-
(24) It is interesting to see the results obtained when using structurally
similar Takemoto’s catalyst (cat. 5) bearing a tertiary amine portion,
which preferentially afforded the trans-epoxide, but with lower
diastereo- and enantiocontrol (see Table 1, entry 3) when compared
to results provided by catalyst 8 (see Table 1, entry 12).
(25) It would be interesting to check the behavior of (E)-unsaturated
pyrazolones, but their synthesis is not a trivial task, as (Z)-unsaturated
pyrazolones are exclusively obtained in Knoevenagel-type reactions.
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