Hydrochloric Acid → Retinal

Participants

Reaction Conditions

Reaction Steps

6-Bromo-3-methyl-1-methoxy-1,3,5-hexatriene (0.257 g; 1.26 mmol) dissolved in ether (10 cc) is introduced, under an argon atmosphere, into a 25 cc round flask fitted with a thermometer and a magnetic stirrer. The flask is cooled to -70° C. tert-Butyllithium (1.2 cc, 1.8N in pentane; 2.1 mmol, i.e. 1.7 equivalent) is then added over 7 minutes while the temperature is kept below -68° C. The solution becomes slightly coloured from pale yellow to light chestnut-brown. It is stirred for 90 minutes at -70° C. β-Ionone (0.23 g; 1.196 mmol, i.e. 0.85 equivalent) dissolved in ether (3 cc) is then added. The mixture is stirred for 90 minutes at -30° C. 1N hydrochloric acid (4.5 cc) is added at -60° C. and the mixture is then stirred vigorously for 1 hour at 10° C. After phase separation, extraction with ether and evaporation of the solvent, a crude product (0.44 g) is obtained, which is purified by flash chromatography on silica, eluting with a mixture of petroleum ether and diethyl ether (98/2 by volume). Retinal (0.187 g) is obtained in this manner in 55% yield. The structure of the product is confirmed by the infrared spectrum and the proton nuclear magnetic resonance spectrum.

Provenance & Evidence