Abstract
A condensation agent prepared by heating polyphosphoric acid (30g. of phosphorus pentoxide in 85% phosphoric acid) with 1/3 to 1/4 its amount of phosphoryl chloride on a water bath for 2 hours was used in heating the ethyl ester of N-acetyl-, -benzoyl-, -phenylacetyl-, and -formyl-L-cystelne at 150-160° (bath tem.) for 2 hours and 2-methyl-, -phenyl-, and -benzyl-thiazoles and thiazole were obtained in a respective yield of 4%, 20%, 10%, and 1%. Similar treatment of the diethyl ester of diacetyi-L-cystine the presence of stannous chloride afforded 2-methylthiazole, though in a small amount.As for the reaction mechanism for this formation of thiazole, it was assumed that it is the same as the formation of the isoquinoline ring from phenylalanine, reported in the preceding paper, since the reaction is accompanied with generation of carbon monoxide.
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