The present invention provides compounds of formula I and pharmaceutically acceptable salts thereof. The formula I compounds inhibit the tyrosine kinase activity of growth factor receptors such as VEGFR-2, FGFR-1, PDGFR, HER-1, HER-2, thereby making them useful as anti-cancer agents. The formula I compounds are also useful for the treatment of other diseases associated with signal transduction pathways operating through growth factor receptors.