Clay plate fragments

Hydroxypyridone ring synthesis. 80 g. phenothiazine, diethyl n-butylmalonate, and unglazed clay plate fragments heated 22 hrs. at 277° crude l-keto-2-n-butyl-3-hydroxy-lH-pyrido[3,2,l-kl]phenothiazine. Y 73%.—Clay plate catalyzes this reaction and particularly prevents decreasing yields of larger batches. F. e., also with phenoxazine, s. M. Harfenist et al., J. Org. Chem. 27, 3977 (1962). 

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