Tin(II) Trifluoromethanesulfonate

Typical procedure (synthesis of (1), R = cyclohexyl): To a flask containing (R)- 1-(1-naphthyl)ethylamine (186 mg) in dried dichloromethane (0.1 M) solution add MS4A (500 mg) followed by cyclohexanecarboxaldehyde (112 mg). After stirring at room temperature for 30 min, 1-methoxy-1-trimethylsilyloxy-1,3-butadiene (258 mg) is added and the mixture solution is cooled to -78 °C. Sn(OTf)2 (412 mg) is then added and the reaction is stirred at this temperature for 8 h. The reaction temperature is raised to -30 °C and kept at the same temperature overnight. The reaction is quenched with a saturated aqueous solution of sodium bicarbonate and the solid is removed via filtration. The reaction mixture is then extracted with ethyl acetate (15 mL x 5). The combined organic phase is dried over sodium sulfate. After concentration, the crude product (dr = 8:1) is purified by silica gel chromatography (eluent: ethyl acetate/hexane = 5/1) to give the major isomer of (1) (258 mg, 71 % yield).