Triethylamine → Methyl 3-isocyanato-3-methylbutanoate

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A solution of 2,2-dimethyl-3-carbomethoxypropionic acid (LeMaul, Bull. Soc. Chim. Fr., 828 (1965), 20 g, 0.125 mol), diphenylphosphorylazide (34.3 g, 0.125 mol) and triethylamine was heated in toluene (150 ml) at 100° C. for 2 h. After cooling to 5° C., the toluene solution was washed successively with 0.5M HCl, aqueous NaHCO3 and brine. Evaporation of the dried solution gave a residue which was chromatographed on silica gel eluting with 60/40 hexane-ether. There was obtained 13 g of methyl 3-isocyanato-3-methylbutanoate as a mobile liquid. A solution of this material in toluene (20 ml) was treated with benzyl alcohol (13 ml) and the resulting mixture heated at reflux for 40 h. Evaporation of the toluene left a residue which was dissolved in methanol (125 ml) and then treated with a solution of NaOH (6.6 g, 0.165 mol) in 22 ml of water. After 5 h, the reaction mixture was partially evaporated, washed with ether and acidified with 6N HCl. Extraction with methylene chloride and evaporation gave 21 g of the desired product. NMR (300 MHz, CDCl3): 1.42 (s,6H), 2.78 (s,2H), 5.08 (s,2H).

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