Disclosed are compounds of Formula (IIIa), wherein R1, R2, R3, X1, X2, X3, X4, X5, have any of the values defined therefore in the specification, and pharmaceutically acceptable salts thereof. The compounds may be used as agents in the treatment of diseases, including cancer. Also provided are pharmaceutical compositions comprising one or more compounds of Formula (IIIa).本發明揭示式(IIIa)化合物,其中R1、R2、R3、X1、X2、X3、X4、X5具有本說明書中為此定義之任何涵義,及其醫藥學上可接受之鹽。該等化合物可用作治療疾病(包括癌症)之藥劑。本發明亦提供包含一或多種式(IIIa)化合物之醫藥組合物。