Formamides are found to undergo addition reactions across alkynes and 1,3-dienes by nickel/Lewis acid catalysis to give a variety of alpha,beta- and beta,gamma-unsaturated amides with stereo- and regioselectivity. Intramolecular insertion reactions of olefins into the C-H bonds of formamides also proceed under similar conditions. The presence of Lewis acid cocatatysts is crucial, and formamide coordination to the Lewis acid is considered to be responsible for the activation of their formyl C-H bonds probably through oxidative addition to nickel(0).