Application of Pd-Catalyzed Cross-Coupling Reactions in the Synthesis of 5,5-Dimethyl-5,6-dihydro-4H-pyrrolo[1,2-b]pyrazoles that Inhibit ALK5 Kinase.

C-H activation of position 3 of a substituted pyrazole ring catalyzed by palladium(II) was straightforward and convenient for arylated or heteroarylated 5,5-dimethyl-5,6-dihydro-4H-pyrrolo[1,2-b]pyrazoles. Moreover, we introduced simple protection of the nitrogen in the pyridin-2-yl directing group, which otherwise does not allow a cross-coupling reaction, by transformation to the N-oxide. Selected final products were reasonably selective ALK5 kinase inhibitors.