(Poly)Borylated Species as Modern Reactive Groups toward Unusual Synthetic Applications

(Poly)borylated species, molecules bearing multiple carbon–boron groups, have emerged as powerful building blocks in modern synthetic chemistry owing to their rich, tunable reactivity. Their distinctive steric and electronic properties, together with their ability to participate in both ionic and radical pathways, make them uniquely versatile synthons for the selective construction of carbon─carbon and carbon─heteroatom bonds. These frameworks provide strategic opportunities for late-stage functionalization and the assembly of architecturally complex molecules. This review highlights recent advances in the chemistry of (poly)borylated compounds, particularly molecules bearing multiple boron substituents on a single carbon site, with emphasis on their anionic, cationic, radical, alkene, 1,2-diradical, and carbene-based variants. It underscores the synergistic behavior of these multiple boron-substituted reactive carbon-centered intermediates and the diverse functionalization of C─metalloid bonds. Key reactivity modes are examined across structural classes such as gem-diborylalkanes, gem-diborylalkenes, 1,1,2-polyborylated systems, and emerging tri- and tetra-borylated frameworks. Central transformations include transition-metal-catalyzed cross-couplings, stereoselective transmetalation and functionalizations, addition reactions, and polymerizations, along with boron-masking, boron-retentive, and boron-eliminative strategies. Furthermore, alkylations, radical-mediated reactions, and energy-transfer photocatalysis pathways are critically discussed. By elucidating the mechanistic principles and synthetic potential of (poly)borylated species, this review aims to provide a unified framework to better understand their reactivity and to highlight the significant advances made since 2019 at the interface of organoboron chemistry, catalysis, and advanced materials science.