Bistrichloromethyl carbonate

To a soln of bistrichloromethyl carbonate (triphosgene) (1.51 g, 5.0 mmol) in EtOAc (280 mL) was added the A -Trt amino acid (14 mmol), then a soln of 1-ethylpiperidine (1.74 g, 15.4 mmol) in EtOAc (20 mL) was added dropwise within 40 min, and the mixture was stirred for another 2 h. The mixture was filtered, the solvent removed and chromatographed on a short column (silica gel, EtOAc). Concentration and crystallization of the residue gave the iV -Trt-NCAs. For example iV-Trt-Ala-NCA (crystallized from EtOAc/petroleum ether) 5neld 71% mp 205-206 °C [a]o -1-34.3 (c 0.5, EtOAc). 

Diisocyanates are usually synthesized by phosgenation of the corresponding diamines. A tabulation of diisocyanates synthesized up to 1972 with pertinent methods of synthesis is available (11). Instead of the toxic phosgene gas, the liquid trichloromethyl chloroformate (diphosgene) (12) or the solid bistrichloromethyl carbonate (triphosgene) (13) can be used in the laboratory (see PHOSGENE). Also, oligomeric t-butylcarbonates are used to convert diamines into diisocyanates (14). 

N-Ethylpiperidine salt of 2-hydroxy-4,6-bistrichloromethyl-s-triazine hydrogenated with 2%-Pd-on-carbon in methanol containing 6 moles of triethyl-amine 2-hydroxy-4,6-dimethyl-s-triazine. Y 84%. Also from the triethylamine salt s. E. Kober, J. Org. Ghem. 25, 1728 (1960). 

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