An efficient cobalt-catalyzed ring-opening reaction of bench-stable 1,2-oxazetidines with heteroarenes was unprecedentedly developed. The sustainable Cp *Co(III) catalyst enables a distinctive merger of C-H activation with concomitant N-O and C-C cleavages of 1,2-oxazetidine, leading to site-selective C-H aminomethylation and hydroxymethylation of heteroaromatic compounds containing a broad range of functional groups. Preliminary control experiments unravel some essential mechanistic features of this one-pot transformation.