As illustrated in Scheme 6, compounds of formula I can be prepared via C???C bond formation by reacting intermediate XIX (where L is a leaving group, such as Br, I or sulfonate) with an activated R1, such as an aryl or heteroaryl boronic acid, or an aryl or heteroaryl tin reagent in the presence of a palladium catalyst (e.g., Pd(PPh3)4).