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

Abstract

International audienceA 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

Cyclisations Catalysed by Bismuth(III) Triflate

“…In 2011, our group described the first examples of catalytic cyclisations involving nonconjugated trienes, initiated by activation of an olefin for the synthesis of functionalised polycyclic compounds. [12b], The mechanism of the reaction was investigated, together with the active species and the role of the bismuth(III) triflate in the process. The first function to be activated was the terminal geranyl moiety, with a subsequent double cyclisation followed by a rearrangement leading to polycyclic compounds in a biomimetic fashion (Scheme ).…”

“…Incidentally, the authors studied the role of Bi(OTf) 3 and came to the conclusion that Lewis acid/base interactions were necessary to generate TfOH in situ (Scheme ). [12c]…”

“…There is some debate in the scientific community as to the nature of the active species in reactions catalysed by metal triflates, concerning the role of triflic acid as a result of a possible hydrolysis versus hydration of the metal triflates in the presence of traces of water . Hydrolysis of Bi(OTf) 3 releases HOTf, which could be responsible for catalytic activity as a Brønsted acid (Scheme ).…”

“…In the particular case of Bi(OTf) 3 , the occurrence of these two processes has been evaluated by density functional theory (DFT) calculations. [12b] Whereas the hydrolysis to triflic acid appeared to be endothermic, hydration was found to be highly favoured. This was also the case with the analogous Sn(OTf) 4 .…”

Access to Polycyclic Derivatives by Triflate‐Catalyzed Intramolecular Hydroarylation

“…[28] A hydrated triflimide salt was proposed to be the active catalyst; this leads to the hypothesis of a hidden Brønsted acid catalysis.…”