Deep eutectic solvents: biorenewable reaction media for Au(I)-catalysed cycloisomerisations and one-pot tandem cycloisomerisation/Diels-Alder reactions

Cycloisomerisation reactions of (Z)-enynols into furans can be conveniently performed, for the first time, in the eutectic mixture 1ChCl/2Gly as a solvent and under standard bench conditions (at room temperature and under air) by using the new bis(iminophosphorane)-Au(I) complex [Au2Cl2(mu(2)-S, S-CH2{ P(=NP(=S)(OPh)(2))Ph-2}(2))] as a catalyst. Furthermore, a one-pot tandem reaction involving the fast cycloisomerisation of (Z)-enynols followed by an intermolecular atom economical process, i.e. the Diels-Alder reaction with activated alkynes or alkenes, is reported. This tandem cycloisomerisation/ Diels-Alder reaction proceeds also in the eutectic mixture 1ChCl/2Gly, in the absence of co-catalysts and under aerobic conditions, giving rise to the corresponding 7-oxanorbornadienes and 7-oxanorbornenes under the principles of the so-called Green Chemistry.