Parallel solid-phase synthesis of 2-arylamino-6H-pyrano[2,3-f]benzimidazole-6-ones

The parallel solid-phase synthesis of a hydrophilic psoralen analogue, 2-arylamino-6H-pyrano[2,3-f]benzimidazole-6-ones (2-arylaminoimidazocoumarins), has been developed. The resin-bound 7-fluoro-4-methyl-6-nitro-2-oxo-2H-1-benzopyran-3-carboxylic acid underwent aromatic substitution with primary amines, followed by reduction of the nitro group with tin(II) chloride. The cyclization of the o-dianilino intermediates was accomplished with aryl isothiocyanates in the presence of 1,3-diisopropylcarbodiimide (DIC). The final products were released from the resin with trifluoroacetic acid (TFA) and obtained in high purity and good isolated yield. The 2-arylaminoimidazocoumarins exhibit interesting spectral properties.