One-Pot Synthesis of Dihydroimidazo- and Imidazophenanthridinium Salts

Abstract

Two highly efficient and general one-pot annulation reactions are described for the synthesis of dihydroimidazo- and imidazophenanthridinium salts (DIPs ⁺ and IPs ⁺). These two methodologies exploit the difference in reactivity between primary amino-based or ammonia nucleophiles and the dielectrophilic starting material, 2-bromoethylphenanthridinium bromide.

Key words

annulation reaction - heterocycles - phenanthridinium derivatives - DNA intercalating agents - anticancer agents

References

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8

Due to resonance electron donation, the amidinium moiety of DIP ⁺s and IP ⁺s makes the positive charge more stable than the one on the iminium moiety of ordinary phenanthridinium derivatives and therefore confers better resistance to the common nucleophilic attack of hydroxide at physiological pH.

14

The quantity of electrophilic reactant added in excess depends on its physical properties: 20 equivalents were used with low boiling point inexpensive material, whereas only 2 equivalents were necessary with solid starting material.

15

With the exception of the electrophile HBr, where r.t. conditions and only 1 min stirring were used on 1 mL of a 48% HBr aqueous solution.