No abstract

Erbium(III) triflate is a powerful catalyst for the acylation of alcohols and phenols. The reaction works well for a large variety of simple and functionalized substrates by using different kinds of acidic anhydrides {Ac 2 O, (EtCO) 2 O, [(CH 3 ) 3 CO] 2 O, Bz 2 O, and (CF 3 CO) 2 O} without isomerisation of chiral centres.Moreover, the catalyst can be easily recycled and reused without significant loss of activity.

The synthesis, characterization, and evaluation of a new highly efficient organocatalyst, namely, (5S)‐2,2,3‐trimethyl‐5‐thiobenzylmethyl‐4‐imidazolidinone hydrochloride, has been achieved. The catalyst possesses important structural features that should increase the catalytic efficiency and solubility in polar media. The application of the ionic‐liquid‐supported imidazolidinone catalyst in enantioselective Diels–Alder reactions was investigated. The Diels–Alder reactions of several dienes and dienophiles proceeded efficiently in the presence of the catalyst to provide the desired products in moderate to good yields and from good to excellent enantioselectivities. The conformation study confirms that in the transition state the Re face is shielded completely by the phenyl ring and an approach on the less hindered Si face is preferred. Particularly remarkable is the fact that the entire ionic liquid/HCl 0.01 M/catalyst system can be recovered and reused in up to six runs without an appreciable loss of catalytic activity.

Aldimines, ketimines, and enaminones can be obtained under erbium(III) triflate catalysis. The reaction mechanism is that typical of imine synthesis. The role of the catalyst is demonstrated for the synthesis of aromatic imines. In contrast to CeCl 3 /NaI addition to unsaturated aldehydes, which results in Michael addition, no Michael adduct was observed under erbium(III) triflate catalysis.

Here, we present a highly efficient approach to nucleobase-containing spiro-isoxazolidines with potential biological activity starting from isatinyl/indanyl nitrones.