3-[(1H-Indol-3-yl)sulfanyl]prop-2-enoic acid → Thiopyrano[3,2-b]indol-4(5H)-one

Participants

Reaction Steps

-- A solution of 76.7 g (0.35 mole) of 3-(indol-3 ylthio) acrylic acid in 4 liters of 10% polyphosphoric acid in acetic acid is stirred at room temperature for 65 hours. The supernatent is decanted from the sticky precipitate, which is partitioned between chloroform and 5% NaOH solution. The organic phase is washed with water, dried, evaporated and the residue recrystallized from 3 liters of 95% ethanol to give 37.8 g of product, mp 242°-243° C.

Provenance & Evidence