Highly enantioselective isomerization of primary allylic alcohols catalyzed by (P,N)-iridium complexes

The catalytic asymmetric isomerization of allylic amines to enamines stands out as one of the most accomplished and well-studied reactions in asymmetric catalysis as illustrated by its industrial application. In contrast, the related asymmetric isomerization of primary allylic alcohols to the corresponding aldehydes still constitutes a significant challenge in organic synthesis. Herein, we show that under appropriate reaction conditions, iridium-hydride catalysts promote the isomerization of primary allylic alcohols under very mild reaction conditions. The best catalysts deliver the desired chiral aldehydes with unprecedented levels of enantioselectivity and good yields. Mechanistic hypotheses have been drawn based on preliminary investigation

A Striking Case of Enantioinversion in Gold Catalysis and Its Probable Origins

The cyclization of the hydroxy-allene 2 to the tetrahydrofuran 3 catalyzed by the gold-phosphoramidite complex 1, after ionization with an appropriate silver salt AgX, is one of the most striking cases of enantioinversion known to date. The major reason why the sense of induction can be switched from (S) to (R) solely by changing either the solvent or the temperature or the nature of the counterion X is likely found in the bias of the organogold intermediates to undergo assisted proto-deauration. Such assistance can be provided by a protic solvent, a reasonably coordinating counterion or even by a second substrate molecule itself; in this case, the reaction free energy profile gains a strong entropic component that can ultimately dictate the stereochemical course

Encapsulation of Crabtree's catalyst in sulfonated MIL-101(Cr): enhancement of stability and selectivity between competing reaction pathways by the MOF chemical microenvironment

Crabtree's catalyst was encapsulated inside the pores of the sulfonated MIL‐101(Cr) metal–organic framework (MOF) by cation exchange. This hybrid catalyst is active for the heterogeneous hydrogenation of non‐functionalized alkenes either in solution or in the gas phase. Moreover, encapsulation inside a well‐defined hydrophilic microenvironment enhances catalyst stability and selectivity to hydrogenation over isomerization for substrates bearing ligating functionalities. Accordingly, the encapsulated catalyst significantly outperforms its homogeneous counterpart in the hydrogenation of olefinic alcohols in terms of overall conversion and selectivity, with the chemical microenvironment of the MOF host favouring one out of two competing reaction pathways

Chiral Pyridyl Phosphinites with Large Aryl Substituents as Efficient Ligands for the Asymmetric Iridium-Catalyzed Hydrogenation of Difficult Substrates

Using a flexible synthesis, new chiral iridium N,P complexes with sterically demanding aryl substituents were synthesized and used in the asymmetric hydrogenation of difficult substrates. Unprecedented enantioselectivities were obtained in the asymmetric hydrogenation of α-substituted α,β-unsaturated esters and dihydronaphthalenes. The variety of aryl substituents incorporated into the catalyst has made it possible to obtain useful structure selectivity relationships for important classes of substrates