1,8-Diaminonaphthalene-masked Boronic Acids

2-(Bromophenyl)-2,3-dihydro-1H-naphtho[1,8-de][1,3,2]diazaborines (1), bromobenzenes bearing a masked boronyl group with 1,8-diaminonaphthalene, were developed by Suginome et al. These masked bromobenzeneboronic acids are useful for oligomer synthesis using the Suzuki–Miyaura cross-coupling reaction. Since the protected boronyl group of 1 is stable under the coupling reaction conditions, the reaction proceeds selectively without the generation of by-products to give the desired coupling products 2 in high yields. The 1,8-diaminonaphthalene group can be easily removed by simple treatment with aqueous acid, and the resulting boronic acids can be used as substrates of subsequent coupling reactions. Thus, a wide range of functionalized oligoarenes can be synthesized selectively by repeating this coupling reaction of boronic acids with derivatives of 1 and de-protection strategy.

Typical Procedure: Synthesis of 2a^1b)
To a mixture of the 1a (100 mg, 0.31 mmol), p-tolylboronic acid (42 mg, 0.31 mmol), CsF (94 mg, 0.62 mmol), and Pd[P(t-Bu)₃]₂ (3.2 mg, 0.0062 mmol) in THF (1.0 mL) is added H₂O (0.20 mL) under a nitrogen atmosphere. The mixture is stirred at 60 °C for 11 h. After cooling to room temperature, water is added to the mixture. After extraction with CHCl₃, the organic phase is dried over MgSO₄ and then filtered through a pad of Celite. Evaporation of the volatile material under vacuum followed by purification by preparative GPC (CHCl₃) affords 2a (98 mg, 95%).