Synlett 2013; 24(10): 1250-1254
DOI: 10.1055/s-0033-1338877
cluster
© Georg Thieme Verlag Stuttgart · New York

Testing New Ruthenium Complexes bearing Chiral 1,2,4-Triazol-5-ylidene ­Ligands as Catalysts for Asymmetric Olefin Metathesis

Rafał Gawin
a  Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland   Fax: +48(22)343-2109   Email: klgrela@gmail.com
,
Michał Pieczykolan
a  Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland   Fax: +48(22)343-2109   Email: klgrela@gmail.com
,
Maura Malińska
b  University of Warsaw, Faculty of Chemistry, Pasteura 1, 02-093 Warsaw, Poland
,
Krzysztof Woźniak
b  University of Warsaw, Faculty of Chemistry, Pasteura 1, 02-093 Warsaw, Poland
,
Karol Grela*
a  Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland   Fax: +48(22)343-2109   Email: klgrela@gmail.com
› Author Affiliations
Further Information

Publication History

Received: 12 April 2013

Accepted after revision: 08 May 2013

Publication Date:
28 May 2013 (online)


Abstract

New ruthenium complexes bearing chiral 1,2,4-triazol-5-ylidene ligands were obtained and tested in model asymmetric metathesis reactions. Low enantioselectivity in asymmetric ring-closing metathesis (ARCM) and moderate enantioselectivity in asymmetric ring-opening/ring-closing metathesis (AROCM) was observed.

Supporting Information

 
  • References and Notes


    • For reviews on asymmetric olefin metathesis, see:
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      Ruthenium carbene complexes bearing achiral 1,2,4-triazol-5-ylidene have been obtained. See:
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  • 13 Synthesis of 7b: (S)-5-sec-Butylmorpholin-3-one (13; 230 mg, 1.46 mmol; see ref. 12) was dissolved in anhyd CH2Cl2 (7 mL) and Me3OBF4 (259 mg, 1.75 mmol) was added. The mixture was stirred at r.t. for 24 h and then cooled to 0 °C. Sat. aq NaHCO3 (10 mL) was added over 15 min and the mixture was further stirred at r.t. for 30 min. The mixture was extracted with CH2Cl2, and the combined organic layers were washed with H2O and dried over Na2SO4. After filtration, the solvent was removed under reduced pressure to afford the crude (S)-3-sec-butyl-5-methoxy-3,6-dihydro-2H-1,4-oxazine (239 mg, 96%) as a white solid which was used in the next step without further purification. Mesitylhydrazine hydrochloride (270 mg, 1.46 mmol) was dissolved in anhyd MeOH (6 mL). The crude (S)-3-sec-butyl-5-methoxy-3,6-dihydro-2H-1,4-oxazine (239 mg, 0.48 mmol) was added in one portion followed by HCl (4 M in 1,4-dioxane; 36 μL, 0.20 mmol, 0.100 equiv) and the reaction mixture was stirred at r.t. for 24 h. The solvent was evaporated to give a yellow solid which was dried in high vacuum. The residue was suspended in chlorobenzene (1.5 mL) and triethyl orthoformate (2 mL, 11.7 mmol) was added. The mixture was stirred for 4 h at 110 °C and concentrated in vacuum. After purification by column chromatography (CH2Cl2–MeOH = 99:1 to 95:5) the desired product was obtained as an off-white solid (160 mg, 33%).
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  • 16 Synthesis of 7d: (S)-5-sec-Butylmorpholin-3-one (13; 692 mg, 4.40 mmol) was dissolved in anhyd CH2Cl2 (10 mL) and Me3OBF4 (651 mg, 4.4 mmol) was added. The mixture was stirred at r.t. for 24 h. Pentafluorophenyl hydrazine (872 mg, 4.40 mmol) was added in one portion and the mixture was further stirred for 24 h at r.t. The solvent was evaporated and residue was dried in high vacuum. Chlorobenzene (5 mL) and triethyl orthoformate (1.8 mL, 11.0 mmol) were added and the mixture was heated to 130 °C for 24 h and then stored overnight in fridge. The precipitated crystals were filtered off and washed with toluene and dried in high vacuum to give the desired product as a white solid (1.40 g, 72%).
  • 17 AROCM of 11 with In Situ Prepared Catalyst 8d: To a solution of bis(tricyclohexylphosphine)benzylidene ruthenium dichloride (8.2 mg, 0.01 mmol, 5 mol%) in anhyd THF (0.5 mL) silver complex 15 (6.2 mg, 0.007 mmol, 3.5 mol%) was added under argon and the reaction mixture was stirred at r.t. for 15 min. After that time the reaction mixture was transferred to a solution of 11 (32.8 mg, 0.2 mmol) and styrene (104.2 mg, 1.0 mmol) in anhyd THF (0.5 mL) and the formed mixture was stirred at 24 °C for 24 h under an argon atmosphere. The reaction was quenched by addition of ethyl vinyl ether and the reaction mixture was concentrated under vacuum. Conversion was determined by 1H NMR while the ee value was determined by HPLC analysis using a chiral column (Daicel Chiralcel® OJ).