Transition-metal catalyzed X-H insertions from alpha-diazocarbonyl compounds represent one of the most efficient approaches to form C--X bonds. The presented thesis is based on the synthesis and application of alpha-diazocarbonyl compounds in metal-catalyzed N-H insertion and the chemoenzymatic synthesis of heterocycles via a Cu]/ Rh] catalyzed intramolecular O-H insertion. In the first part, a straightforward approach via the Wittig reaction, gamma-Umpolung addition and diazo transfer reaction allowed the synthesis of unsaturated alpha-diazocarbonyl compounds with ease. In the second part, the newly synthesized (R textsubscript{p)-pseudo-ortho 2.2]paracyclophane-based bisoxazoline ligands presented superior reactivity. The obtained delta-amino alpha, beta-unsaturated carboxylic esters were used to synthesize hexahydroindoles, which are key intermediates in the synthesis route of Rostratin B-D. Additional investigation of alpha-diazocarbonyl compounds led to the enzymatic synthesis of O-Heterocycles. With the employment of enantiopure starting material obtained from ketoreductase LbADH, the enantioselectivity of each diastereomer from the O-H insertion product have been effectivity improved.