Pd(ii)-catalyzed cycloisomerisation of γ-alkynoic acids and one-pot tandem cycloisomerisation/CuAAC reactions in water

Abstract

Cycloisomerisation reactions of γ-alkynoic acids into cyclic enol-lactones can be conveniently performed in pure water as a solvent and under aerobic conditions by using a novel iminophosphorane–Pd(II) complex trans-[PdCl₂{μ²-N,S-(PTA)NP(S)(OEt)₂}]₂ as a catalyst. It is important to note that the catalytic system could be recycled up to 10 consecutive runs. In addition and for the first time, a one-pot tandem orthogonal reaction involving the fast cycloisomerisation of γ-alkynoic acids, followed by an intermolecular atom economical process, i.e. the 1,3-dipolar cycloaddition of azides with terminal alkynes (CuAAC), is reported. This new tandem cycloisomerisation/click reaction proceeds also in water, at room temperature and under aerobic conditions, giving rise to unprecedented bicyclic triazol-enol-lactones under the principles of the so called “Green Chemistry”.