Citronellal → (-)-Isopulegol

HRID 1822171Notes

Reaction equation

C([Al](CC)CC)C.[CH3:8][C:9](=[CH:11][CH2:12][CH2:13][CH:14]([CH2:16][CH:17]=[O:18])[CH3:15])[CH3:10].C(OC(=O)C)(=O)C.[OH-].[Na+]>C1(C)C=CC=CC=1>[CH3:15][C@H:14]1[CH2:16][C@@H:17]([OH:18])[C@H:11]([C:9]([CH3:10])=[CH2:8])[CH2:12][CH2:13]1

Participants

Conditions

Temperature: 0 °C

Procedure

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).

Workup

additionwas added
stirringThe mixture was after-stirred for 1 h at 0° C. and for 12 h at room temperature
customthe phases separated
dry with materialThe organic phase was dried with sodium sulfate
customthe solvent was removed under reduced pressure
distillationThe crude product was distilled at 1 mbar over a short column

Sources & evidence

ORD record: ord-9c85ff499afa41ce94c7592292e3a394
Source dataset: uspto-grants-2009_10
DOI: 10.6084/m9.figshare.5104873.v1
Patent number: US07608742B2

Reaction notes

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