Ethynyl‐B(dan) in [3+2] Cycloaddition and Larock Indole Synthesis: Synthesis of Stable Boron‐Containing Heteroaromatic Compounds

Abstract

AbstractThe cycloaddition of nitrile oxides with ethynyl‐B(dan) (dan=naphthalene‐1,8‐diaminato) allowed the facile preparation of diverse isoxazolyl‐B(dan) compounds, all of which displayed excellent protodeborylation‐resistant properties. The dan‐installation on the boron center proves vital to the high stability of the products as well as the perfect regioselectivity arising from hydrogen bond‐directed orientation in the cycloaddition. The diminished boron‐Lewis acidity of ethynyl‐B(dan) also renders it amenable to azide‐alkyne cycloaddition, Larock indole synthesis and related heteroannulations. The obtained boron‐containing triazole, indoles, benzofuran and indenone exhibit sufficient resistance toward protodeborylation. Despite the commonly accepted transmetalation‐inactive property derived from the diminished Lewis acidity, the synthesized heteroaryl‐B(dan) compound was still found to be convertible to the oligoarene via sequential Suzuki‐Miyaura coupling.