Acyl group migration affects the synthesis, isolation, manipulation and purification of all acylated organic compounds containing free hydroxyl groups, in particular carbohydrates. While several isolated studies on the migration phenomenon in different buffers have been reported, comprehensive insights into the overall migration process in different monosaccharides under similar conditions have been lacking. Here, we have studied the acyl migration in different monosaccharides using five different acyl groups by a combination of experimental, kinetic and theoretical tools.The results show that the anomeric configuration in the monosaccharide has a major influence on the migration rate, together with the relative configurations of the other hydroxyl groups and the nature of the migrating acyl group. Full mechanistic model, based on computations, demonstrates that the acyl migration proceeds through an anionic stepwise mechanism with linear dependence on the [OH À ] and the pK a of the hydroxyl group toward which the acyl group is migrating.

A total regioselective synthesis of 1,4,5‐trisubstituted‐1,2,3‐triazoles from aryl azides and enaminones is reported. The use of an ionic liquid in the presence of water and trimethylamine is crucial for the progress of the reaction. The process, consisting of a cascade starting with a water‐promoted 1,3‐dipolar cycloaddition (in agreement with DFT calculations) followed by a base‐promoted retro‐aza‐Michael reaction, shows a completely different reactivity to previously reported base‐promoted reactions between enaminones and sulfonyl azides only leading to disubstituted triazoles. Such reactivity, reported herein, allows preparation of trisubstituted triazoles in a complete regioselective way.

This review covers recent computational studies evidencing the presence of glycosyl cations as real intermediates in several glycosylation reactions.

The catalyzed desymmetrizative ring expansion of alkenylcyclobutanols promoted by halofunctionalization of the alkene moiety with N -bromosuccinimide has been experimentally and computationally studied. The reaction yields highly enantioenriched cyclopentanones bearing two all-carbon quaternary stereocenters, one of them being generated in the rearrangement of the cyclobutane ring and the other by enantioselective desymmetrization. The reaction is competitive with the formation of a spiroepoxide, but it turns completely selective toward the cyclopentanone when a chiral bisphosphonium magnesium salt is employed as a catalyst. Mechanistic studies support the formation of an ion pair leading to a complex with only a unit of phosphoric acid, which is the resting state of the catalytic cycle. Calculations reproduce in an excellent way the observed reactivity and predict the effect exerted by the substituents of the aromatic ring linked to the double bond. The computational studies also revealed the reaction as a highly asynchronous concerted process taking place as one kinetic step but in two stages: (i) halogenation of the double bond and (ii) rearrangement of the cyclobutane. No intermediates are present in the reaction as energy minima. The experimental scope of the reaction further confirms the predictions for the observed reactivity and selectivity.