1. Catalyst Preparation: Lanthanum nitrate hexahydrate (La(NO3)3-6H2O, 17.3 mg, 0.04 mmol) and tri-n-octylphosphine (90% purity, 40 μL, 0.08 mmol) were added to a Soxhlet reflux vessel containing degreased cotton wool and 2.0 g of dried granular molecular sieve 5A. Dimethyl carbonate (8 mL), dehydrated by distillation, was added and stirred for 1 to 2 min at room temperature. The mixture was heated under heated reflux conditions (bath temperature 110°C) for 1 hour. Cool to room temperature, distill under reduced pressure to remove the solvent, and dry at room temperature for 1 hour at 5 torr or less to obtain the catalyst.
2. Reaction Procedure: In a reaction vessel, n-hexane (8 mL) was added sequentially as solvent, 4-nitrobenzoate (4.0 mmol) as carboxylic acid ester, and benzyl alcohol (4.0 mmol) as primary alcohol. The reaction was immediately heated to reflux conditions (bath temperature: 90 °C). The progress of the reaction was monitored by TLC and the completion of the reaction was confirmed after 5 hours. Cool to room temperature, add a small amount of water (0.3 to 0.5 mL) and stir for 5 min at room temperature to terminate the reaction. The reaction mixture was dried with magnesium sulfate, filtered and the filtrate was concentrated. The product was purified by silica gel column chromatography (hexane: ethyl acetate) in 99% yield.
3. For Examples 25-29 and Comparative Examples 10-14, the operation was the same as in Example 24, with only the carboxylate and reaction time changed. In Example 30 and Comparative Example 15, methyl benzoate was used as the carboxylic acid ester, cyclohexanol was used as the secondary alcohol, and the reaction time was adjusted. In Examples 26, 27, 29 and Comparative Examples 11, 12, 15, the amount of lanthanide compound and ligand was increased. The results are summarized in Table 4, including the results of Example 24 and Contrast Ratio 9.
