Bisethylenyl Phthalides

Introduction of two diaminophenylethylene moieties at the 3-position of the phthalide ring naturally also produces color formers exhibiting infrared absorption. As in Section 4.6.1, the first report93 encompasses a vast number of compounds such as 22 which was prepared by treating phthalic anhydride with 2 mol of 1,1-bisdimethylaminophenylethylene in acetic anhydride. 

Finally, bisindolylethylenes have also been reacted with tetrahaloph-thalic anhydrides to yield color formers showing absorption in the near infrared.99 The chief advantage over the diarylethylenes is the availability of the starting materials. The bisindolylethylenes may be prepared in situ by reaction of an indole with acetyl chloride and then converted directly to the phthalide without isolation. 

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