Toluene → Lilac acetaldehyde

Beteiligte Stoffe

Reaktionsschritte

To a solution of ethyl 4-methylphenylacetate (0.89 g, 5.0 mmol) in dry methylene chloride (5 ml) cooled to −78° C. under nitrogen was added drop-wise 1.1 M di-isobutyl-aluminum hydride in toluene (4.5 ml, 5 mmol), keeping the internal temperature below −68° C. When the addition was complete, the reaction was quenched by drop-wise addition of methanol (5 ml), saturated potassium sodium tartrate solution (5 ml), and water (5 ml). The mixture was filtered through filter aid, the pad was washed with ethyl acetate (40 ml), and the filtrate layers were separated. The aqueous layer was extracted with ethyl acetate (40 ml). The combined ethyl acetate layers were washed with water (20 ml), and brine (20 ml), dried (sodium sulfate), filtered, and the solvent evaporated under reduced pressure to give 7.1 g of 4-methylphenylacetaldehyde as a volatile liquid: 1H NMR (CDCl3) 9.73 (1H, t, J 2.5 Hz), 7.17 (2H, m), 7.12 (2H, m), 3.64 (2H, d, J 2.5 Hz), 2.35 (3H, s). To a stirred mixture of benzyl (trans-3-{[tert-butyl(dimethyl)silyl]oxy}cyclopentyl)carbamate (524 mg, 1.5 mmol), triethylsilane (0.36 ml, 260 mg, 2.25 mmol), and bismuth tribromide (45 mg, 0.10 mmol), in anhydrous acetonitrile (7.5 ml), was added the freshly prepared 4-methylphenylacetaldehyde (460 mg, approx. 2.2 mmol) slowly, keeping the temperature at or below 25° C. After stirring for 4 h, the reaction was quenched with half-saturated sodium bicarbonate (30 ml) and ethyl acetate (25 ml). The mixture was filtered through filter aid, the pad was washed with ethyl acetate (3×8 ml), and the filtrate layers were separated. The organic layer was washed with one-fifth saturated brine (8 ml) and water (8 ml), dried (sodium sulfate), filtered, and the solvent evaporated under reduced pressure to give a heterogeneous oil (1.19 g). The oil was chromatographed on silica gel, eluting with ethyl acetate:hexane (5:95 increasing to 25:75) to give a white solid. The solid was triturated with ethyl acetate:hexane (20:80), filtered off and dried to give benzyl {trans-3-[2-(4-methylphenyl)ethoxy]cyclopentyl}carbamate (291 mg, 55%) as a white solid. A second crop was obtained from the mother liquor (34 mg, 6%).

Herkunft & Nachweise