Abstract
The Ph3 P/TiCl4 combination was found to be an effective promoter for the Claisen-type condensation of α-bromothioesters. Both in the case of self-condensation and crossed-type reactions, corresponding β-ketothioesters were obtained in good yields.
Key words
Claisen condensation - Lewis acids - titanium tetrachloride - thioesters - phosphines
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7 Typical Procedure for the Self-Claisen Condensation: Under an argon atmosphere, to a solution of S -phenyl-2-bromopropanethioate (2a , 95.0 mg, 0.39 mmol) and TiCl4 (5 mol/L, 0.12 mL, 0.6 mmol) in DCE (3 mL) was added a solution of Ph3 P (151.6 mg, 0.58 mmol) in CH2 Cl2 (1 mL). The reaction mixture was stirred for 1 h and quenched with water (3 mL) and ethylene glycol (2 mL). The mixture was extracted with CH2 Cl2 (3 × 10 mL), washed with brine (10 mL), and dried over MgSO4 . The organic layer was filtered and evaporated under reduced pressure. The crude product was purified by preparative TLC (SiO2 , CH2 Cl2 -hexane = 1:1) to give S -phenyl-2-methyl-3-oxopentanethioate (3a , 32.6 mg, 76%).
