Fulgides synthesis

Synthesis of the dibenzofuran (27) by irradiation of grisa-3, 5 -diene-2, 3 -dione (28) is believed to involve electrocyclic ring opening followed by intramolecular cycloaddition to the ketene and elimination of carbon dioxide, as shown in Scheme 2.24 Analogous photocyclizations are responsible for the photochromism exhibited by heterocyclic fulgides such as ( )-a-3-furyl-ethy idene(isopropylidene)succinic anhydride (29), which on irradiation... 

Elucidate the synthesis of the fulgide and give a mechanistic explanation for its photochromic behaviour. 

Scheme 3 Synthesis of photoisomerizable Concanavalin A by the chemical linkage of photoisomerizable thiophene fulgide or nitrospiropyran residues to the protein.

Fulgide Family Compounds Synthesis, Photochromism, and Applications... 

Indolyl-substituted heterocyclic fulgides have been studied by several research groups.65-69 Wang et al.10 and Fan et al11 reported the synthesis and crystal structures of azafulgide 54. The structures and photochromic reactions are shown in Scheme 16. 

Yokoyama and Kurita demonstrated the design, synthesis, and photochromic behavior of 5-substituted indolyl fulgides (56). The molecular structure and photochromic reactions are shown as Scheme 17. 

Recently Fan et al.,78,79,81 84,86,87 Zhao et al.,so and Fan et al.85 have made an effort to study the molecular design, synthesis, photochromism, and application of pyrryl-substituted fulgides. A series of such fulgides (62) has been prepared by Fan s group, and the photochromic reactions investigated. The molecular structures and photochromic reactions are shown in Scheme 20. 

The first investigations that led to the synthesis, characterization, and properties of fulgides were carried out on phenyl and substituted phenyl fulgides. Therefore it is essential to describe the synthetic procedure for the preparation of phenyl (substituted phenyl) fulgides. This will be beneficial to understanding the later modifications of the synthetic methods for the heterocyclic-substituted fulgides. Some representative examples follow. 

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