SNAr nucleophilic substitution of 1,9-dihalodipyrrins by S- and N- nucleophiles. Synthesis of new dipyrrins bearing pendant substituents

• Free 1,9-dichlorodipyrrins indergo nucleophilic substitution by S- and N-nucleophiles.
• S-nucleophiles yield disubstitution, i.e. 1,9-dithiadipyrrins are the products.
• N-nucleophiles quantitatively substitute only one chlorine atom.
• UV–Vis spectra of bis-S-substituted products shift bathochromically as to that of dichlorides.
• Mono-N-substituted products with H-bonding group feature two bands in the UV–Vis spectra.

5-Aryl-1,9-dichlorodipyrrins react with a series of S- and N- nucleophiles (both alkyl- and aryl- ones). Reagents with mercapto group yield product of double nucleophilic substitution of 5-pheny-1,9-dichlorodipyrrin, i.e. the respective 1,9-bis(alkyl-of arylthio)dipyrrin. On the contrary, 5-(4-nitrophenyl)-1,9-dichlorodipyrrin causes disulfides formation from the S-aliphatic substrates, whereas nucleophilic substitution remains the main path of the reaction for S-aryl ones. The reaction of N-Alkyl nucleophiles proceeds as mono-substitution. UV–Vis spectra feature a batochromic shift for bis-S-substituted products and a hypsochromic shift for mono-N-substituted ones, with respect to the starting dichlrorides.

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