Phthalazine complex formation

With this in mind, the coordination chemistry of 52 with different diazine structural isomers was investigated. There were no detectable changes in the H NMR spectrum of 52 in a THF-Jg solution when either pyrazine or pyrimidine were added in 1 1 or 1 2 molar ratios, which suggested that only weak interactions might occur between 52 and these bases. In contrast, incremental addition of pyridazine or phthalazine to a THF-Jg solution of 52 at 25 °C resulted in an upheld shift of the aromatic NMR resonances of the diindacycle 52 thus reflecting the formation of complexes between 52 and the 1,2-diazines. Analysis of the tritration data clearly indicated the formation of 1 1 Lewis acid-diazine complexes 52-pyridazine-(THF)2 and 52-phthalazine-(THF)2 whose stability constants are equal to 80 ( 10) and 1000 ( 150) M respectively (Scheme 29). These data, as a whole, indicate that 52 is a selective receptor for 1,2-diazines. 

Figure 5. CD within the near-UV region of azanaphthalenes after formation of inclusion complexes with B-cyclodextrin. Spectra are shown for (a) quinoline, (b) phthalazine, (c) isoquinoline, and (d) cinnoline (data adapted from reference [38]).

Unequivocal evidence for the formation of o -adducts has been obtained by X-ray diffraction analysis of those adducts which are stable enough to obtain their single crystals [11]. Indeed, the X-ray crystallography data are available for the anionic trinitrobenzene-methoxide and the Janovsky trinitrobenzene-acetone complexes [11, 201, 202] and for the o -adducts of isoquinoline [203], phthalazine [160], and 4,7-phenanthroline [161, 162] with dialkyl phosphonates. Also the X-ray data have been obtained for the neutral o -adducts resulting from the reactions of iV-methylacridinium ion with N-nucleophiles [204, 205] and for the o -adducts of iV-alkyl-substituted 2,3-dicyanopyrazinium and quinoxalinium salts with 0-, C-and P-nucleophiles [163, 194]. 

Multicomponent approaches toward the formation of more complex phthalazine-containing compounds were reported in 2014. A four-component one-pot condensation reaction was employed by Dabiri and coworkers to generate (1,2,3-triazol-4-yl)methyl-3-amino-5,10-dihydro-5,10-dioxo-lH-pyrazolo[l,2-f)]phthalazine-2-carboxylates 26 (Scheme 18) (14SC2037). Catalyzed by Cu(OAc)2 (10mol%) and sodium ascorbate (20mol%), the reaction of benzaldehyde derivatives (1 equivalent), azides (1 equivalent), prop-2-ynyl-2-cyanoacetate (27) (1 equivalent), and phthalhydrazide (28) (1... 

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