1,1-Hydroboration of Fused Azole-Isoindole Analogues as an Approach for Construction of B,N-Heterocycles and Azole-Fused B,N-Naphthalenes

Three isoelectronic analogues of pyrido[2,1-a]isoindole have been found to undergo a facile 1,1-hydroboration with HBMes₂ borane, which provides a new and convenient method for the synthesis of B,N-heterocycles 1a-3a in high yields. Compounds 1a-3a can undergo photoelimination upon irradiation at 300 nm, generating heterocycle-fused B,N-naphthalene molecules 1b-3b, which display distinct yellow-green and blue fluorescent colors, respectively. Compound 1a undergoes thermal elimination, producing 1b at 280°C, while compound 2a only undergoes partial elimination, forming 2b at 320°C. Compound 3a is thermally stable up to 320°C.