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Synlett 2010(5): 707-711  
DOI: 10.1055/s-0029-1219363
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Thieme Chemistry Journal Awardees - Where Are They Now? Bifunctional Organocatalysis with N-Formyl-l-Proline: A Novel Approach to Epoxide Ring Opening and Sulfide Oxidation

Shengwei Wei, Kerstin A. Stingl, Katharina M. Weiß, Svetlana B. Tsogoeva*
Department of Chemistry and Pharmacy, Chair of Organic Chemistry I, University of Erlangen-Nuremberg, Henkestr. 42, 91054 Erlangen, Germany
Fax: +49(9131)8526865; e-Mail: tsogoeva@chemie.uni-erlangen.de;
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Publication History

Received 9 October 2009
Publication Date:
08 February 2010 (online)

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Abstract

A conceptually distinct approach to the aminolysis of 1,2-epoxides, which involves Lewis base-Brønsted acid catalysis employing N-formyl-l-proline as an easily accessible bifunctional organocatalyst and water as a solvent is presented. The potential of N-formyl-l-proline as organocatalyst for the sulfide oxidation reaction using aqueous hydrogen peroxide as environmentally benign and readily available oxidant is also demonstrated. Good to high yields are achieved for both reactions.

Key words

bifunctional organocatalysis - Lewis base-Brønsted ­acid - epoxides - ring opening - amino alcohols - sulfide oxidation - ­sulfoxides

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General Procedure for the Aminolysis of 1,2-Epoxides A mixture of epoxide (0.31 mmol, 1 equiv), amine (2 equiv), and N-formyl-l-proline (0.1 equiv) in H2O (150 µL) was stirred at r.t. for 24 or 48 h. The reaction mixture was diluted with H2O (1.5 mL) and extracted with CH2Cl2 (3 × 2 mL). The combined organic layers were washed with brine (2 mL), dried (Na2SO4), and the solvent was removed under reduced pressure. The residue was purified by chromatog-raphy (SiO2, PE-EtOAc) to provide the desired β-amino alcohols in yields given in Table  [²] . Products from the entries 1-5 and 7-13 are known compounds. Their constitution was ascertained by comparison of spectroscopic data with reported literature data.7h, ¹³ β-Amino alcohol from entry 6 is a new compound, and its characterization data are reported below.
¹H NMR (300 MHz, DMSO-d 6): δ = 7.26 (t, 1 H, J = 7.5 Hz), 6.29-6.35 (m, 2 H), 5.65 (br s., 1 H), 3.24-3.45 (m, 2 H), 2.23 (s, 3 H), 1.85-1.96 (m, 2 H), 1.60-1.63 (m, 2 H), 1.08-1.22 (m, 4 H) ppm. ¹³C NMR (75 MHz, DMSO-d 6):
δ = 158.33, 154.56, 137.41, 110.26, 105.50, 73.21, 56.18, 34.20, 30.97, 24.13, 23.71 ppm. MS (MALDI): m/z = 207 [M + H]+; the exact molecular mass m/z = 206.1419 ± 1.7 ppm [M+] was confirmed by HRMS (EI, 70 eV).

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A Typical Procedure for the Oxidation of Methyl Phenyl Sulfide To a solution of catalyst (0.048 mmol) in a solvent (500 µL) methyl phenyl sulfide (0.242 mmol) was added at r.t. To this mixture 30% H2O2 (29.6 µL, 1.2 equiv) was added in one portion and stirred for 24 h at r.t. After quenching the reaction with Na2SO3, the conversion was determined by GC analysis using hexadecane 99% (30 µL) as internal standard. The yield of isolated product was obtained directly by column chromatography (PE-EtOAc, 1:1). The isolated methyl phenyl sulfoxide was identified through comparison of ¹H NMR spectra with literature data. See ref. 10g,k,m.