Citronellal → (-)-Isopulegol

Participants

Reaction Conditions

Reaction Steps

8.0 g (13.6 mmol) of the ligand Ia2-3 were dissolved in 140 ml of toluene at room temperature under argon. 4.78 ml (9.09 mmol) of a 25% strength triethylaluminum solution in toluene were added and the mixture was after-stirred for 1 h. The resulting catalyst suspension was cooled to 0° C. and, over the course of 5 h, a mixture of 70.0 g (0.45 mol) of citronellal and 0.7 g (6.86 mmol, 1% by weight with regard to citronellal) of acetic anhydride was added. The mixture was after-stirred for 1 h at 0° C. and for 12 h at room temperature. At the end of the experiment, 100 ml of 8% strength sodium hydroxide solution were added and the phases separated. The organic phase was dried with sodium sulfate and the solvent was removed under reduced pressure. The crude product was distilled at 1 mbar over a short column. At a top temperature of 58° C., 68.4 g of isopulegol with the following composition (in each case GC area %) were obtained: isopulegol: 98.4%, neo-isopulegol: 0.6%, neoiso-isopulegol: 0.4%. This corresponds to a chemical yield of 97%, based on all diastereomers and a diastereoselectivity of 99:1 (isopulegol: other diastereomers).

Provenance & Evidence