General Procedure for the Synthesis of Trichloroacetimidates from the Corresponding Alcohol. A flame-dried 25 mL round bottom flask was charged with the alcohol starting material (1equiv) under argon. Dry DCM was then added to form a 0.5 M solution, and the flask was cooled to 0 °C. DBU (0.2 equiv) was added to the solution, followed by trichloroacetonitrile (1.5 equiv). The reaction was monitored by thin-layer chromatography (TLC). After completion of the reaction, the reaction mixture wasconcentrated and silica gel column chromatography was performed to provide the desired trichloroacetimidates.
General Procedure for Esterification by Method A. In a flame-dried flask, the trichloroacetimidate (2 equiv) was dissolved in dichloromethane (0.25 M) under argon. The carboxylic acid (1equiv) was then added, and the mixture was stirred at room temperature. The reaction progress was monitored by thin layer chromatography. After completion, the reaction mixture was poured into 2 N NaOH and extracted with DCM (3×). The combined organic extracts were then dried over sodium sulfate, filtered, and concentrated. The residue was purified by silica gel column chromatography to give the ester product.
General Procedure for Esterification by Method B. The carboxylic acid (1 equiv) and trichloroacetimidate (2 equiv) were placed in a flame-dried round bottom flask under argon. Anhydrous toluene (0.25 M) was then added and the reaction was heated to reflux. The reaction progress was monitored by thin layer chromatography. After disappearance of the carboxylic acid, the mixture was allowed to cool to rt, poured into 2 N NaOH, and extracted with DCM (3×). The combined organic extracts were then dried over sodium sulfate, filtered, and concentrated. The residue was purified by silica gel column chromatography to give the ester product.