The construction of a novel class of aminophosphite/phosphinite/phosphine ligands containing a protected pyrrolidine-3,4-diol moiety is presented. These ligands are obtained from readily available sugars. They thus contain the advantages of carbohydrates in terms of selection of the stereogenic carbons, polyfunctional groups able to modulate the electronic and steric properties, and the general good stability of carbohydrate derivatives. They constitute a novel class of P,Nligands that have been used in the enantioselective allylic substitutions of acyclic and cyclic substrates with varied electronic and steric requirements, using different C-and N-nucleophiles, with high enantioselectivities. Among the three groups of P,Nligands (amino-P; P = phosphite, phosphinite, and phosphine groups) the new amino-phosphite ligands give the widest substrate and nucleophile scope, including the more challenging hindered linear and cyclic substrates. In particular, for carbohydratederived amino-phosphite ligands and linear substrates, high enantioselectivity in the reactions requires an R configuration of the binaphthyl moiety. However, for cyclic substrates both product enantiomers can be reached by setting out the chirality of the binaphthyl phosphite moiety. A detailed investigation of the appropriate Pd intermediates is also presented.
Modulable monosulfonyl squaramides have been shown to
exert activation
of gold(I) chloride complexes through H-bonding in an intermolecular
way. Combinations of (PPh3)AuCl or IPrAuCl complexes and
an optimal sulfonyl squaramide cocatalyst bearing two 3,5-bis(trifluoromethyl)phenyl
groups efficiently catalyzed diverse heterocyclizations and a cyclopropanation
reaction, avoiding in all cases undesired side reactions. Computational
studies indicate that the Au–Cl bond breaks by transligation
to the triple bond in a ternary complex formed by the actual AuCl···HBD
catalyst and the substrate.
The synthesis of a small library of (pyrrolidin-2-yl)triazoles via copper catalysed cycloaddition of an alkynyl iminocyclopentitol and a set of commercial and synthetic azides has been achieved. The in situ screening for the activity towards α-fucosidase of the resulting triazoles has allowed the identification of one of the most potent and selective pyrrolidine derived inhibitors of this enzyme (Ki = 4 nM).
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