The Ir-MaxPHOX-type catalysts demonstrated high catalytic
performance
in the hydrogenation of a wide range of nonchelating olefins with
different geometries, substitution patterns, and degrees of functionalization.
These air-stable and readily available catalysts have been successfully
applied in the asymmetric hydrogenation of di-, tri-, and tetrasubstituted
olefins (ee′s up to 99%). The combination of theoretical calculations
and deuterium labeling experiments led to the uncovering of the factors
responsible for the enantioselectivity observed in the reaction, allowing
the rationalization of the most suitable substrates for these Ir-catalysts.
Air-stable and readily available Ir-catalyst precursors modified with MaxPHOX-type ligands have been successfully applied in the challenging asymmetric hydrogenation of tetrasubstituted olefins under mild reaction conditions. Gratifyingly, these catalyst precursors are able to efficiently hydrogenate not only a range of indene derivatives (ee's up to 96%) but also 1,2-dihydronapthalene derivatives and acyclic olefins (ee's up to 99%), which both constitute the most challenging substrates for this transformation. Letter pubs.acs.org/OrgLett
A family of phosphite/phosphinite‐thioether ligands have been tested in the Ir‐catalyzed asymmetric hydrogenation of a range of olefins (50 substrates in total). The presented ligands are synthesized in three steps from cheap indene and they are air‐stable solids. Their modular architecture has been crucial to maximize the catalytic performance for each type of substrate. Improving most Ir‐catalysts reported so far, this ligand family presents a broader substrate scope, covering different substitution patterns with different functional groups, ranging from unfunctionalized olefins, through olefins with poorly coordinative groups, to olefins with coordinative functional groups. α,β‐Unsaturated acyclic and cyclic esters, ketones and amides were hydrogenated in enantioselectivities ranging from 83 to 99% ee. Enantioselectivities ranging from 91 to 98% ee were also achieved for challenging substrates such as unfunctionalized 1,1′‐disubstituted olefins, functionalized tri‐ and 1,1′‐disubstituted vinyl phosphonates, and β‐cyclic enamides. The catalytic performance of the Ir‐ligand assemblies was maintained when the environmentally benign 1,2‐propylene carbonate was used as solvent.
We
have identified a successful family of simple P-stereogenic N-phosphine–phosphite ligands for the Rh-catalyzed
asymmetric hydrogenation of olefins. These catalysts show excellent
enantiocontrol for α-dehydroamino acid derivatives and α-enamides
(ee’s up to >99%) and promising results for the more challenging
β-analogues (ee’s up to 80%). The usefulness of these
catalytic systems was further demonstrated with the synthesis of several
valuable precursors for pharmacologically active compounds, with ee’s
at least as high as the best ones reported previously (up to >99%).
We
studied for the first time the potential of novel and simple
Ir/thioether-NHC complexes in the asymmetric hydrogenation of unfunctionalized
olefins and cyclic β-enamides. For comparison, we prepared and
applied the analogues thioether–phosphinite/phosphite complexes.
We found that the efficiency of the new Ir/thioether-NHC catalyst
precursors varies with the type of olefin. Thus, while the Ir/thioether-NHC
catalyst precursors provided lower catalytic performance than their
related Ir/thioether-P complexes in the hydrogenation of olefins lacking
a coordinating group, the catalysts had similar good performance for
the reduction of functionalized olefins (e.g., tri- and disubstituted
enol phosphonate derivatives). Catalytic results together with the
studies of the reactivity toward H2 indicated that the
thioether-carbene design favors the formation of inactive trinuclear
species, which are responsible for the low activities obtained with
these carbene-type catalysts. Nevertheless, this catalyst deactivation
can be avoided by using functionalized olefins such as enol phosphonates.
We also report the discovery of simple-to-synthesize Ir/thioether-P
catalysts containing a simple backbone that gave high enantioselectivities
for some trisubstituted olefins, some challenging 1,1′-disubstituted
olefins, and cyclic β-enamides.
High enantioselectivities (up to 99 %) and activities (TOF's up to >4000 h−1) are accomplished in the Pd‐catalyzed allylic substitution of a wide range of substrate types and nucleophiles using a family of phosphite‐oxazoline ligands. These ligands were derived from the PHOX ligand by exchanging the phosphine moieties by biaryl phosphites and a methylene spacer was introduced between the oxazoline and the phenyl ring. The wide substrate scope is due to the ability of the ligand family to adapt their ligand parameters to the reacting substrate. This ability also explains its high performance in other type of catalytic processes.
Herein, we report a chiral phosphine-triazole ligand for the Ir-catalyzed asymmetric hydrogenation of exocyclic benzofused alkenes. Overcoming previous limitations, the catalytic system is able to successfully hydrogenate exocyclic olefins bearing a benzofused five-and six-membered ring motif (ee's between 92 to 99%). The catalyst tolerates well the presence of several substituents and substitution patterns at both aromatic rings. The absence of a competing isomerization process together with the perfect fit of the olefins in the catalyst chiral pocket are key to surpass the previous limitations in the hydrogenation of both 5-and 6membered ring benzofused exocyclic olefins.
The front cover picture, designed by Jèssica Margalef, illustrates the usefulness of a modular and easy‐to‐assemble catalyst design for asymmetric hydrogenation. By choosing the appropriate sulfur and phosphorus substituents on new Ir‐P,S‐catalysts, it is possible to hydrogenate substrates of very different nature (50 olefins in total). Improving on most catalysts reported so far, di‐ and E/Z‐trisubstituted olefins with a variety of functional groups and coordination ability can be reduced with excellent enantioselectivities. Details can be found in the Research Article by Diéguez and co‐authors (J. Margalef, M. Biosca, P. de la Cruz‐Sánchez, X. Caldentey, C. Rodríguez‐Escrich, O. Pàmies, M. A. Pericàs, M. Diéguez, Adv. Synth. Catal. 2021, 363, 4561–4574; DOI: 10.1002/adsc.202100069)
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