Studies on Indole Derivatives. XXIII. Diels-Alder Reaction of 3-Indoledithiocarboxylic Acid Derivatives and Dimethyl Acetylenedicarboxylate and Reactions of Their Products - MATSUDA, YOSHIRO; TOMINAGA, YOSHINORI; KOBAYASHI, GORO; NATSUKI, REIKO (Chemical & pharmaceutical bulletin, 1973)