Fulgenolides. Thermally Irreversible Photochromic Lactones with Large Quantum Yields of Photoreactions.

Three new photochromic lactones closely related to an indolylfulgide were synthesized. While the lactones with the carbonyl group adjacent to the isopropylidene group have large quantum yields of photoreactions, the isomer with the carbonyl adjacent to the indolylethylidene group showed poor photochromic properties. The absorption maxima of the colored forms of the lactones are shorter than that of the indolylfulgide.