Boronic Acids as Green Catalysts for the Synthesis of Heterocyclic Compounds: A Review

Heterocyclic compounds play a significant role in the structures of pharmaceuticals, agrochemicals, natural products, and functional materials. The traditional methods used to synthesize these compounds often involve strong acids, transition-metal catalysts, high temperatures, large amounts of activating agents, and harmful solvents. Boronic acids have become valuable metal-free catalysts because the trivalent boron in them functions as a Lewis acid and can temporarily bind to oxygen-containing compounds. These features allow boronic acids to activate various functional groups such as carbonyl compounds, alcohols, carboxylic acids, diols, and 1,3-dicarbonyl compounds during reactions like condensation, cyclization, dehydration, and multicomponent reactions. This review explores the use of boronic acids and related organoboron catalysts in the synthesis of heterocyclic compounds, including dihydropyrimidinones, 1,4-dihydropyridines, tetrahydrobenzo[b ]pyrans, benzimidazoles, pyranopyrazoles, quinolines, and azoles.Different types of boronic acids such as phenylboronic acid, substituted arylboronic acids, boric acid, and borinic acids are compared based on how they activate substrates, the range of substrates they can work with, and their environmental benefits. Although boronic-acid catalysts help reduce reliance on toxic metals and large amounts of reagents, their environmental impact must still be evaluated based on factors such as solvent selection, energy consumption, ability to recover the catalyst, purification needs, and green chemistry metrics [1–5].