We report an Ir(I)-catalyzed kinetic resolution of secondary allylic carbonates allowing for their isolation in up to 98% ee. Importantly, the study documents the synthesis and use of a new class of chiral [2.2.2]-bicyclooctadiene ligands for iridium.
Metal-catalyzed asymmetric processes offer one of the most straightforward ways to introduce stereogenic centers. Hence, the development of novel chiral ligands that can effectively induce asymmetry in reactions is crucial in modern organic synthesis. While many established chiral ligands bind to a metal through heteroatoms, structures that coordinate to metals through carbon atoms have received little attention so far. Here, we highlight the increasing number of such chiral chelating olefin ligands as well as their application in a variety of metal-catalyzed transformations.
Two for the price of one: Sulfamic acid serves not only as a nitrogen source but also as an in situ activator of hydroxy groups in the first direct iridium‐catalyzed synthesis of primary allylic amines from allylic alcohols (see scheme; cod=cycloocta‐1,5‐diene). The reaction is catalyzed by a commercially available iridium complex and a phosphoramidite‐based bidentate phosphorus–olefin ligand.
[reaction: see text] We document a series of investigations that led to new substituted [2.2.2]-diene ligands which display high selectivity in Rh(I)-catalyzed conjugate addition reactions to substrates not previously examined with diene ligands. Moreover, we disclose an unexpected, interesting effect that results from the introduction of a third C=C onto the ligand scaffold (cf. 1).
A general route to enantioenriched 3,3-diarylpropanals is presented. These useful building blocks are prepared via an asymmetric rhodium-catalyzed conjugate addition of arylboronic acids to cinnamaldehyde derivatives in the presence of chiral dienes. The addition of both electron-poor as well as electron-rich boronic acids proceeds smoothly with various enals in 63-90% yield with high enantioselectivities (89-93% ee).
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