This dissertation presents the development of new homologation strategies in boron chemistry that expand the classical Matteson-type reactions into unprecedented structural spaces with precise stereocontrol. Through three complementary studies, we demonstrate the programmable construction of alkenyl and tertiary boronates via carbenoid insertions and metallate rearrangements, enabling efficient access to complex, functionally rich molecules. In the first part, we report a diastereoselective vinylene homologation of alkyl and aryl boronates. This method employs sequential insertion of a silyl- and an alkoxy-substituted carbenoid, followed by Peterson-type elimination, to afford a diverse array of alkenyl boronates with excellent E/Z selectivity. Computational investigations revealed how Lewis acid choice governs the transition between SN2-type and SN1-type 1,2-migration, providing mechanistic insights into the stereochemical outcome. This method has been applied in an iterative fashion to streamline the synthesis of piperamide natural products. The second project describes a stereospecific alkenylidene homologation strategy via a concerted metallate SNV (nucleophilic vinylic substitution) mechanism. By harnessing strain-release in alkenyl-ate complexes, this reaction achieves inversion of stereochemistry and enables the iterative incorporation of alkenylidene units into organoboron frameworks. The resulting cross-conjugated polyenes are typically difficult to synthesize and demonstrate the utility of this approach for modular alkene assembly. Applications to bioactive motifs further illustrate the synthetic potential of this platform. In the third study, we developed an enantioselective synthesis of tertiary boronates using configurationally labile α-thio lithium carbenoids. A ligand-controlled thermodynamic resolution, promoted by chiral hydrobenzoin-derived diethers, enables enantioconvergent homologation of boronates with excellent enantioselectivities. Mechanistic studies elucidate the dynamic behavior of tertiary carbenoids and reveal a concerted, stereospecific 1,2-migration promoted by Lewis acids. This platform offers a robust method for constructing quaternary stereocenters and complements existing strategies in asymmetric synthesis. Collectively, these studies significantly advance the field of boron-based chain elongation chemistry. By extending the scope of Matteson-type homologation to include vinylene, alkenylidene, and tertiary carbenoid systems, this work lays the groundwork for programmable and stereocontrolled synthesis of complex boron-containing molecules relevant to pharmaceutical and materials science applications.