To prepare 21, a different route was employed, which is included in the middle of Scheme 3. A dimethylamino alkyne group was installed on the indole using a Sonogashira coupling reaction to obtain 68. Bromination was accomplished using NBS, and the indole nitrogen was protected to yield intermediate 70. This intermediate was subsequently used in a Stille reaction with 4-(tributylstannyl)pyrimidine to provide 21.