Reactions of 1, 1-Bismethylthio-2-nitroethylene. IV. Syntheses and Reactions of 4-Methylthio-2-buten-4-olide Derivatives - SONE, MASAKATSU; MATSUDA, YOSHIRO; TOMINAGA, YOSHINORI; KOBAYASHI, GORO; NATSUKI, REIKO (Chemical & pharmaceutical bulletin, 1974)