Trifluoroacetic acid → D-tryptophanyl-trans-2,5-dicarbethoxypyrrolidine

Participants

Reaction Conditions

Reaction Steps

A 25% solution of TFA in CH2Cl2 (25 ml) was added at 0° C. to an isomeric mixture 0.94 g (1.9 mmol) of the tryptophan pyrrolidine diester (2) and 0.41 (3.8 mmol) anisole. The reaction mixture was stirred at 0° C. for 15 min and then at room temperature for 2. hr. TLC analysis (93:7, CHCl3 /MeOH) using a ninhydrin indicator showed the complete disappearance of the starting material and the appearance of a new spot near the baseline. Without isolation of this material, the TFA was neutralized by the addition of 12.12 ml of diisopropylethylamine and the mixture turned from dark red to yellow. After stirring at room temperature for approximately six hours, TLC analysis of the reaction mixture (95:5;CHCl3 /MeOH) showed the presence of two major isomers in approximately a 2:1 ratio. After removal of the CH2Cl2 in vacuo, the suspension was extracted into ethyl acetate and washed and dried over anhydrous MgSO4. Concentration in vacuo resulted in 0.88 g of a dark brown oil. Column chromatography over silica gel (CHCl3) produced 0.30g (44%) of the trans isomer that yielded the following 1H NMR (CDCl3, 360 MHz) data:

Provenance & Evidence