Borverbindungen, 9. Metathetische Ring‐Ring‐Gleichgewichte bei Dioxaboracycloalkanen

Aryldihydroxyboranes (2,10) condense with α,ω-alkanediols HO(CH2)xOH (6), which leads to an equilibrium of oligomeric rings (7) of different size due to a ligand exchange at the boron atom. With low diols (6, x = 2,3) the rate of establishing the equilibrium of the exchange reaction is slow enough for isolating the five- and six-membered heterocycles (7, n = 1). Diols with x≥5, however, lead to the equilibrium mixture of oligomeric heterocycles in a somewhat analogous way to olefin metathesis.