Binol → (-)-Isopulegol

Participants

Reaction Steps

In a 300-ml reaction flask, 2.29 g (8.0 mmol) of (R)-1,1′-bi-2-naphthol was placed and the air in the flask was replaced with nitrogen gas. Then, 116 ml of toluene and 5 ml (5.0 mmol) of a toluene solution of triethylaluminum (1.0 mol/L) were successively added thereto and the mixture was stirred at room temperature for 1 hour, to give a catalyst solution. After the catalyst solution was cooled to a temperature of 0 to 5° C., 38.6 g (250 mmol) of d-citronellal was slowly added dropwise thereto, and the mixture was stirred at a temperature of 0 to 5° C. for 9 hours. After completion of the reaction, the reaction mixture was concentrated in vacuo, and continuously toluene was distilled off at a temperature of 110 to 115° C. at a pressure of 2.93 to 3.33 kPa (22 to 25 mmHg), to give 31.0 g of the objective l-isopulegol at the yield of 80.3%. The GC analysis results show that the purity was 99.0% and that the ratio of l-isopulegol to the other isomers was 98.7:1.3.

Provenance & Evidence