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Synlett 2009(14): 2291-2294  
DOI: 10.1055/s-0029-1217806
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Enantioselective Iodolactonizations of 4-Pentenoic Acid Derivatives Mediated by Chiral Salen-Co(II) Complex

Zhaolun Ning, Rizhe Jin, Jinying Ding, Lianxun Gao*
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Graduate School of Chinese Academy of Sciences, 130022 Changchun, P. R. of China
Fax: +86(431)85685653; e-Mail: lxgao@ciac.jl.cn;
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Publication History

Received 27 March 2009
Publication Date:
07 August 2009 (online)

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Abstract

This work presents the salen-Co(II) complex catalyzed enantioselective iodolactonizations of various 4-pentenoic acid derivatives with good enantioselectivities (up to 83% ee).

Key words

asymmetric catalysis - salen complex - synthesis - lactones - iodolactonization

10

Compounds 1a-d were purchased from Aldrich.

13

Compounds 2 and 4a-f were prepared from the correspond-ing 4-substituted-4-oxo-butanoic acid ethyl ester via Witting methylenation followed by basic cleavage of the ethyl ester.

15

General Procedure for Iodolactonization of Substituted 4-Pentenoic Acid Salen complex 1a (41.1 mg, 0.068 mmol) and NCS (5.7 mg, 0.043 mmol) was dissolved in toluene (8.0 mL), and stirred at r.t. for 30 min. After cooling down the resulting solution to -18 ˚C with ice salt bath, I2 (60.5 mg, 0.238 mmol) was added as solid to the solution, and stirred at -18 ˚C for 5 min. Compound 2 (30.0 mg, 0.170 mmol) was added to the mixture and cyclized for an additional 20 h at -18 ˚C. The reaction mixture was quenched with 10% aq Na2S2O3 (20 mL) and extracted with CH2Cl2 (3 × 20 mL). The organic layer was separated and washed with sat. aq Na2CO3. After removal of solvent in vacuo, the resulting crude product was purified by chromatography on silica gel (elution with EtOAc-PE = 1:5) to give lactone 3 (44.6 mg, 87%). The ee was determined by HPLC analysis [hexane-2-PrOH = 9:1; Chiralcel OD-H; 1.0 mL/min; 254 nm; t R (S*) = 18.7 min; t R (R*) = 21.4 min].