On the Catalysis of the Cycloisomerization of 1,6-Dienes with Tin(IV) Salts: The Important Role of a Water Molecule

Abstract : A diene cycloisomerisation reaction catalysed by tin(IV) triflimi- date is studied by using DFT computations. It is proposed that the mechanism does not involve the direct addition of the tin(IV) cation to a double bond because the catalyst regenera- tion step would be energetically unfeasible. We show that a water molecule may play a decisive role to enable the smooth completion of the catalytic cycle. The proposed active catalyst is thus a hydrated triflimidate salt. The hydrolysis and hydration energies are computed for three ligands of SnL4, L= triflate (OTf), triflimidate (NTf2) and a chlorosulfonate model (OSO2Cl). The diastereoselectivity observed in the cycloisomeri- sation is discussed in light of the transition-state geometries. The hypothesis of hidden Brønsted acid catalysis is discussed and ruled out on the basis of new experimental results.