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Synlett 2008(4): 555-560  
DOI: 10.1055/s-2008-1032074
LETTER
© Georg Thieme Verlag Stuttgart · New York

Catalytic Enantioselective Mukaiyama-Michael Reaction of 2-(Trimethyl­silyloxy)furan with α′-Phenylsulfonyl Enones

Hyeyeon Yang, Sunggak Kim*
Center for Molecular Design & Synthesis and Department of Chemistry, School of Molecular Science, Korea Advanced Institute of Science and Technology, Daejeon 305701, Korea
Fax: +82(42)8698370; e-Mail: skim@kaist.ac.kr;
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Publikationsverlauf

Received 5 November 2007
Publikationsdatum:
23. Januar 2008 (online)

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Abstract

The Mukaiyama-Michael reaction of 2-(trimethylsi­lyloxy)furan with α′-phenylsulfonyl enones using bis(oxazoline)-copper(II) complexes as chiral catalyst provides the γ-butenolides in high enantio- and diastereoselectivity. This approach is very useful for the enantioselective synthesis of γ-butenolide derivatives under chiral Lewis acid catalysis.

Key words

asymmetric catalysis - Michael additions - Lewis acids - ligands - lactones

18

Typical Procedure for the Mukaiyama-Michael Reaction of 2-(Trimethylsilyloxy)furan (3) with α′-Phenylsulfonyl Enone 5a: To the flask of freshly prepared [(4R,5S)-diPhBox]Cu(OTf)2 (5 mol%) in CHCl3 (1 mL) was added a solution of α′-phenylsulfonyl enone 5a (0.11 mmol, 25 mg) in CHCl3 (1 mL). After being stirred at r.t. for 0.5 h, the reaction mixture was cooled to 0 °C, and the solution of 3 (0.22 mmol, 35 mg) in CHCl3 (1 mL) was added to the reaction mixture. The reaction was maintained at the desired temperature until a complete consumption of the α′-phenylsulfonyl enone 5a as monitored by TLC. After completion of the reaction, the reaction was quenched with sat. aq NaHCO3 solution, extracted with CH2Cl2, washed with H2O, dried over MgSO4, filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography to give 6a as an oil in 99% yield (34 mg). Spectroscopic data for 6a: 1H NMR (400 MHz, CDCl3): δ = 1.01 (d, J = 6.9 Hz, 3 H), 2.41 (m, 1 H), 2.60 (dd, J = 18.8, 7.2 Hz, 1 H), 2.84 (dd, J = 18.8, 5.3 Hz, 1 H), 4.14 (dd, J = 21.4, 13.3 Hz, 2 H), 4.90 (dd, J = 6.1, 3.2 Hz, 1 H), 6.08 (dd, J = 5.8, 1.9 Hz, 1 H), 7.43 (d, J = 5.9 Hz, 1 H), 7.56 (t, J = 8.0 Hz, 2 H), 7.67 (t, J = 7.7 Hz, 1 H), 7.84 (d, J = 7.4 Hz, 2 H). 13C NMR (100 MHz, CDCl3): δ = 16.02, 31.88, 46.12, 66.86, 85.73, 122.26, 128.05, 129.34, 134.32, 138.60, 154.66, 172.39, 196.34. IR (KBr): 3700, 3139, 3022, 2953, 2360, 1731, 1612, 1566, 1490, 1432, 1353, 1223, 1116, 1060, 1005, 946, 870, 783, 720, 669 cm-1. HRMS (ESI): m/z [M + H]+ calcd for C15H17O5S: 309.0798; found: 309.0791. Product ratio was determined by HPLC analysis (Chiralcel OD-H, 30%
i-PrOH-hexane, 0.6 mL/min, λ = 254 nm); S,S-isomer (major): t R = 42.4 min and R,R-isomer (minor): t R = 53.7 min; [α]D 25 +58.7° (c = 1.0 in CH2Cl2).