Dibal reduction of an amino acid derived methyl ester; Garner's Aldehyde
Submitted Sep 05, 2001, published Sep 05, 2001
DIBAL (1 M solution in toluene)
Potassium sodium tartrate (Rochelle's salt)
A solution of 3-(1,1-dimethyl-4-methyl)-(S)-2,2-dimethyloxazolidine-3,4-dicarboxylate (22.4 g, 86.15 mmol) in dry toluene (180 mL) in a 1 litre round bottomed flask was cooled under an atmosphere of argon to -78°C. A solution of DIBAL in toluene (147 mL of a 1 M solution) was added over 1 hour (see notes). The reaction was stirred for a further 2 hours at -78°C, before being quenched by the dropwise addition of dry methanol (33 mL). The reaction was allowed to warm to about -20°C internal temperature, and then poured into a vigorously stirred solution of Rochelle's salt (1.2M aqueous potassium sodium tartrate, 600 mL). The viscous solution was stirred vigorously for 2 hours, after which time it settled to two clear phases. The organic layer was separated, and the aqeous layer extracted three times with diethyl ether (150 mL each extraction). The combined organics were dried over magnesium sulfate and evaporated. Purification by distillation (83-85 °C, 0.2 mmHg) gave Garner's aldehyde (16.30g, 82%) as a colourless oil.
1H (CDCl3, 300 MHz) 9.62 and 9.55 (1H, br s, CHO), 4.36 and 4.20 (1H, m), 4.09 (2H, m), 1.63 and 1.60 (3H, s), 1.57 and 1.51 (3H, s), 1.52 and 1.45 (9H, s). Most peaks are doubled due to restricted rotation of NBOC group. IR (thin film, cm-1) 1740 (CHO), 1710 (BOC).
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Keywords: 161, aldehyde, DIBAL, Garner's, reduction