Abstract
<jats:p>This chapter explores the diverse reactivity of Fischer-type metal carbene complexes in the synthesis of nitrogen-containing heterocycles. Emphasis is placed on the role of carbene ligands in key cyclization strategies, including [3+2], [4+2], and [5+5] annulations. Various approaches using aminocarbene, imino-carbene, and β-functionalized alkenylcarbene complexes are discussed, highlighting their ability to undergo regio- and stereoselective transformations with imines, hydrazines, isocyanides, and alkynes. The chapter also outlines mechanistic pathways involving carbene insertions, cycloadditions, and metal-templated reactions, leading to the construction of pyrroles, azepines, pyrazoles, and isoquinolines. Particular attention is given to ligand effects, ring-size control, and strategies for optically pure products through chiral auxiliaries. These findings underscore the synthetic utility and mechanistic richness of Fischer carbene chemistry in heterocycle construction.</jats:p>