O,N,B-Containing eight-membered heterocycles by ring expansion of boroles with nitrones.

By a ring expansion reaction of boroles with nitrones a straightforward route to eight-membered O,N,B-containing ring systems was developed, which present a new structural motif in heterocyclic chemistry. Formally, these compounds can be considered as BN-analogues of eight-membered ring ethers containing three double bonds. The X-ray crystallographic data of a series of these oxazaborocine derivatives show that they adopt a boat conformation in the solid state.