Synthesis and Photochromic Properties of Fulgides with a t-Butyl Substituent on the Furyl- or Thienylmethylidene Moiety

Abstract 2,6,6-Trimethyl-5-(2,5-dimethyl-3-furyl and -3-thienyl)-3-heptyn-2,5-diols were carbonylated in benzene in the presence of 1 : 1 — Pd(OAc)2/I2 as the catalyst. The reaction at 90 °C under 80 atm of carbon monoxide for 5 h directly gave both E and Z isomers of t-butyl-substituted furyl- or thienyl fulgides. The former had been reported impossible to synthesize by the Stobbe condensation. Similarly, furyl- and thienylfulgides with an isopropyl group were synthesized by this method. The fulgides were isolated by column chromatography in 37—75% yields. Coloring quantum yields of t-butyl-furyl- and -thienylfulgides are 0.79 and 0.73, respectively, which are the greatest in each series of fulgides with the same heteroaromatic ring.