Benzimidazole 2-styryl

If 1,2-diaminobenzene is condensed with butyrolactone and the product qua-temized, a benzimidazole derivative with a reactive methylene group is obtained. Condensation of this compound with 4-aminobenzaldehydes (which can also be dimerized via the nitrogen atom) produces styryl dyes (e.g.,31) which, on account of ring closure, can be classified as monomethinehemicyanine dyes. These dyes are used to dye paper [75] ... 

The l,3-dimethyl-2-substituted styryl benzimidazolium salts (xxxii), a useful hemocyanine dyes have been synthesized by the solvent free microwave assisted condensation of 1,2,3-trimethyl benzimidazole salts with aromatic aldehydes in the presence of piperidine [38]. 

The reactions of 2-methylbenzimidazole or 2-methylbenzimidazolium iodide with aromatic aldehydes are accelerated under MW irradiation by using or piperidine as a dehydrant or catalyst in the absence of any solvent [104]. The approach provides an attractive and environmentally friendly pathway to several useful styryl dyes with benzimidazole nucleus (Scheme 3.44). 

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