Benzene → (-)-Dihydroquinine

Participants

Reaction Steps

A solution containing 1.25 g. of dihydroquinidinone in 50 ml. of benzene containing 0.5 ml. of methanol was maintained at 20° for 21/2 days under nitrogen. The solution was evaporated to complete dryness under vacuum, and the residue was redissolved in benzene and again evaporated to dryness. The resulting oily residue was dissolved in 50 ml. of dry benzene, and 3 ml. of a 25% solution of di-isobutyl aluminum hydride in toluene were added dropwise with stirring under an atomsphere of dry nitrogen. The reaction was quenched after about 30 minutes by adding 10 ml. of water-methanol (1:1), and the mixture was stirred vigorously for 30 minutes. The benzene layer was decanted. The aqueous aluminum suspension was washed several times with benzene and the combined benzene phases were dried over anhydrous magnesium sulfate and evaporated to dryness. The crude product (1.25 g. of colorless foam) was a practically pure mixture of dihydroquinidine and dhydroquinine (about 1:1) as determined by thin layer chromatography; and a specific rotation [α]D24,5 + 62.2° (c 1.64, ethanol). Crystallization from ethanol yielded 490 mg. of pure dihydroquinidine having a melting point of 167°-169°. Chromatographic separation from mother liquors gave 550 mp of dihydroquinine, m.p. 168°-170°, [α]D29 -137.5°.

Provenance & Evidence