The reaction of a phenol, and α,β-unsaturated aldehyde, and phenylboronic acid yields a 2-phenyl-4H-1,3,2-benzodioxaborin. Upon heating, this compound decomposes to an orthoquinone-methide intermediate, which undergoes an electrocyclization reaction to a chromene ring system. This method has been applied to the synthesis of precocenes I and II and the robustadial A and B.
Manganese dioxide mediated one-pot synthesis of methyl 9H-pyrido[3,4-b]indole-1-carboxylate: Concise synthesis of alangiobussinine