[O:1]=[C:2](Cl)OC(Cl)(Cl)Cl.Cl.[CH3:10][O:11][C:12](=[O:24])[CH:13]([N:21]=[N+]=[N-])[CH2:14][C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=1>C(OCC)(=O)C.C(OC)(=O)C.[Re]([O-])(=O)(=O)=O.[Na+]>[CH3:10][O:11][C:12](=[O:24])[C:13]([N:21]=[C:2]=[O:1])=[CH:14][C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=127.3 mg (0.1 mmole) of sodium perrhenate and 1.04 grams (5.25 mmoles) of diphosgene were present at 80° C. in 1 ml of ethyl acetate saturated with hydrogen chloride. Then there were added within 20 minutes with vigorous stirring 2.05 grams (10 mmoles) of 2-azido-3-phenylpropionic acid methyl ester dissolved in 5 ml of methyl acetate. After reaction for 1 hour at 80° C., the mixture was worked up analogous to Example 1. The crude produce was distilled in a high vacuum (0.0013 mbar) at 90° to 110° C. apparatus temperature in a bulbed tube. There resulted 1.08 grams (53.2% of theory) of analytically pure 2-isocyanato-3-phenylpropenoic acid methyl ester.
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