Merging furan rings with 1,2,7-oxa- and -azadiborepins. This modular synthesis proceeds through a reversible ring-opening process and furnishes the novel heteropolyaromatic compounds from a common precursor. The tricyclic systems are overall aromatic, and weak aromaticity in the diboron heterocycles favors π electron delocalization over the bifuran unit. The π-conjugated system is easily extended through the α-positions of the furan rings.
A modular synthesis of both difurooxa- and difuroazadiborepins from a common precursor is demonstrated. Starting from 2,2′-bifuran, after protection of the positions 5 and 5’ with bulky silyl groups, formation of the novel polycycles proceeds through opening of the furan rings to a dialkyne and subsequent re-cyclization in the borylation step. The resulting bifuran-fused diborepins show pronounced stability, highly planar tricyclic structures, and intense blue light emission. Deprotection and transformation into dibrominated building blocks that can be incorporated into π-extended materials can be performed in one step. Detailed DFT calculations provide information about the aromaticity of the constituent rings of this polycycle.Zum Volltext