6'-Bromo-2',2'-dimethyldispiro[cyclopropane-1,3'-chromene-4',4''-[1,3]oxazol]-2''-amine → (4'R)-6'-bromo-2',2'-dimethyldispiro[cyclopropane-1,3'-chromene-4',4''-[1,3]oxazol]-2''-amine

Participants

Reaction Steps

To a solution of 6′-bromo-2′,2′-dimethyldispiro[cyclopropane-1,3′-chromene-4′,4″-[1,3]oxazol]-2″-amine (3.7 g, 11 mmol) in methanol (50 ml) was added (+)-dibenzoyl-D-tartaric acid monohydrate (4.1 g, 11 mmol). The mixture was stirred at room temperature for 5 minutes and concentrated in vacuo. To the residue was added dioxane (25 ml). The mixture was heated under reflux for 5 minutes, cooled to room temperature and stirred at room temperature overnight. The resulting precipitate was collected, washed with dioxane, and dried in vacuo. The resulting powder was dissolved in saturated aqueous sodium hydrogen carbonate and chloroform. The mixture was extracted with chloroform, and the organic layer was dried over anhydrous magnesium sulfate, and concentrated in vacuo to afford (4′R)-6′-bromo-2′,2′-dimethyldispiro[cyclopropane-1,3′-chromene-4′,4″-[1,3]oxazol]-2″-amine (1.5 g). The mother liquor was concentrated in vacuo and purified by NH-silica gel column chromatography (CHCl3/MeOH=20:1). The purified material was treated with (−)-dibenzoyl-L-tartaric acid monohydrate (2.0 g, 5.4 mmol) in the same manner as described above which lead to isolation of (4′S)-6′-bromo-2′,2′-dimethyldispiro[cyclopropane-1,3′-chromene-4′,4″-[1,3]oxazol]-2″-amine (1.2 g).

Provenance & Evidence