Development of Two Complementary Syntheses for a Privileged CGRP Receptor Antagonist Substructure

1-(Piperidin-4-yl)-1H-imidazo[4,5-b]pyridin-2(3H)-one (1) is a privileged substructure found in >1000 unique CGRP receptor antagonists. Two practical and efficient syntheses of 1 are described from complementary starting materials. One route features a chemoselective reductive amination, while the second route utilizes a Pd-catalyzed amination using an ammonia surrogate to overcome an issue of poor selectivity.