Nucleophilic addition of organolithium reagents to cyanine dyes. A new access to functionalized hexatrienes

The possibility for extending a pentamethine carbon chain by the use of an appropriate pair of electrophilic substrates, a cyanine dye- and nucleophilic-organolithium reagent is explored. A new synthetic approach to differently functionalized hexatrienes was achieved as a result of spontaneous or accelerated on silica gel surface Hofmann type elimination of the initially formed adducts. A series of trifunctional ligands were obtained by means of a two-step reduction with Pd/C and LAH.