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U. Bremberg et al.
PAPER
(2) (a) Seyden-Penne, J. Chiral Auxiliaries and Ligands in
(S)-3-Phthalimidocyclohex1-ene
Pd2Cl2(C3H5)2 (3.3 mg, 0.0090 mmol), 8 (18.6 mg, 0.0269 mmol),
phthalimide (106.0 mg, 0.720 mmol) and cyclohex-2-en-1-yl ethyl
carbonate (61.3 mg, 0.360 mmol) were added to a dry reaction ves-
sel, together with MeCN (1.8 mL). The reactants were allowed to
mix for 30 sec before the vessel was sealed with a septum and irra-
diated. After cooling, the reaction mixture was diluted with Et2O to
a total volume of 10 mL and 4-methoxybenzonitrile (29.0 mg, 0.218
mmol) was added as an internal standard for the GC determination
of the yield. Alternatively, the product was isolated by diluting with
EtOAc (50 mL) and washing with NaOH (2 M, 3 î 50 mL), drying
(MgSO4) and evaporation, followed by chromatography (gradient
of 5-20% EtOAc in hexanes). HPLC was used to analyze the enan-
tiopurity (Chiralcel OD-H, 1 mL/min, 1.5% i-PrOH in hexanes).
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(S)-3-(Phenylsulfonyl)cyclohex-1-ene
(b) Kaiser, N.-F. K.; Bremberg, U.; Larhed, M.; Moberg, C.;
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Pd2dba3•CHCl3 (4.8 mg, 0.052 mmol) and 8 (10.0 mg, 0.0145
mmol) were stirred together in MeOH (1 mL) for 15 min. A solution
of benzenesulfinic acid was prepared by adding CF3CO2H (44 mg,
0.39 mmol) to a solution of sodium benzenesulfinate (63.1 mg,
0.384 mmol) in MeOH (1 mL). The two solutions were mixed in the
reaction vessel and cyclohex-2-en-1-yl ethyl carbonate (34.0 mg,
0.200 mmol) was added. The reaction vessel was sealed with a sep-
tum and irradiated for 2 min at 30 W. Isolation of the product by
chromatography (EtOAc/hexanes, 1:8) gave 82% yield. Analysis by
NMR and addition of 0.17 equivalent of Eu(hfc)3 showed the enan-
tiopurity to be 70% ee. Performing the reaction in MeCN afforded
higher selectivity (88% ee), but the results were not always repro-
ducible.
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Caution! When carrying out microwave heated reactions in closed
vessels thermal stress and/or high pressures can be generated. Un-
less an appropriate pressure release device is used, e. g. a septum,
an explosion can result. It is recommended to proceed with caution
and keep the microwave reactor in an efficient fume hood.
Acknowledgement
This work was supported by the Swedish Natural Science Research
Council (CM), the Swedish Research Council for Engineering Sci-
ences (AH) and by Personal Chemistry AB, Uppsala, Sweden. The
authors are grateful to Professor Martin Nilsson for enthusiastic
support.
References
(1) (a) Noyori, R. Asymmetric Catalysis in Organic Synthesis,
Wiley: New York, 1994.
(b) Ojima, I. Catalytic Asymmetric Synthesis, VCH: New
York, 1993.
Article Identifier:
1437-210X,E;2000,0,07,1004,1008,ftx,en;C01200SS.pdf
Synthesis 2000, No. 7, 1004–1008 ISSN 0039-7881 © Thieme Stuttgart · New York