Metal-Free Construction of Oxazole Ring by Formal [2+2+1] Cycloaddition

Saito et al. have reported a metal-free synthesis of oxazole rings by a formal [2+2+1] cycloaddition. The reaction is mediated by a catalytic in situ generated iodine (III) species to cyclize an alkyne and nitrile moieties affording di or trisubistuted oxazoles with good yield and complete regioselectivity. It was experimentally determined that the hypervalent iodine moiety is formed in situ by the treatment of a catalytic amount of iodobenzene with mCPBA and bis(trifluoromethanesulfonyl)imide (= Tf₂NH). This result represents the first example of a multicomponent reaction using a hypervalent iodine (III) compound.