Tomislav Rovis

Correction for ‘Ligand design for Rh(III)-catalyzed C–H activation: an unsymmetrical cyclopentadienyl group enables a regioselective synthesis of dihydroisoquinolones’ by Todd K. Hyster et al., Chem. Sci., 2015, 6, 254–258.

Correction for ‘Ligand design for Rh(III)-catalyzed C–H activation: an unsymmetrical cyclopentadienyl group enables a regioselective synthesis of dihydroisoquinolones’ by Todd K. Hyster et al., Chem. Sci., 2015, 6, 254–258.

Carboxylates effectively direct C–H activation for rhodium(III)-catalyzed intramolecular Heck-type reactions. A catalytic amount of Cu(OAc)₂ is used as the external oxidant with oxygen likely acting as the terminal oxidant. Additionally, a novel electron-deficient rhodium(III) catalyst was found to be more effective than [RhCp*Cl₂]₂ with some substrates. A wide variety of complex dihydrobenzofurans, dihydrobenzopyrans, and other bicycles that can be easily further functionalized are now accessible through relatively mild reaction conditions.

We report a catalytic asymmetric synthesis of piperidines through [4 + 2] cycloaddition of 1-azadienes and nitro-alkenes. The reaction uses earth abundant Zn as catalyst and is highly diastereo- and regioselective. A novel BOPA ligand (F-BOPA) confers high reactivity and enantioselectivity in the process. The presence of ortho substitution on the arenes adjacent to the bis(oxazolines) was found to be particularly impactful, due to limiting the undesired coordination of 1-azadiene to the Lewis acid and thus allowing the reaction to be carried out at lower temperature. A series of secondary kinetic isotope effect studies using a range of ligands implicates a stepwise mechanism for the transformation, involving an initial Michael-type addition of the imine to the nitro-alkene followed by a cyclization event. The stepwise mechanism obviates the electronic requirement inherent to a concerted mechanism, explaining the successful cycloaddition between two electron-deficient partners.

Correction for ‘Pyridine synthesis from oximes and alkynes via rhodium( iii ) catalysis: Cp* and Cp ^t provide complementary selectivity’ by Todd K. Hyster et al., Chem. Commun. , 2011, 47 , 11846–11848.

The discovery of new catalytic reactions involving the use of abundant, inexpensive, and sustainable metal complexes has enjoyed a resurgence of activities in recent years. This Cluster, the second of a two-part series, continues the update of this important field, communicating a variety of approaches that address this important challenge.

An enantioselective isomerization of 4-iminocrotonates catalyzed by a rhodium(I)/phosphoramidite complex is described. This reaction uses widely available amines to couple with 4-oxocrotonate to provide a convenient access to a central chiral building block in good yield and high enantioselectivity. Although the mechanism of this new transformation remains unclear, both Rh and the phosphoramidite play a central role.

Asymmetric hydroheteroarylation of alkenes represents a convenient entry to elaborated heterocyclic motifs. While chiral acids are known to mediate asymmetric addition of electron-rich heteroarenes to Michael acceptors, very few methods exploit transition metals to catalyze alkylation of heterocycles with olefins via a C–H activation, migratory insertion sequence. Herein, we describe the development of an asymmetric, intermolecular hydroheteroarylation reaction of α-substituted acrylates with benzoxazoles. The reaction provides 2-substitued benzoxazoles in moderate to excellent yields and good to excellent enantioselectivities. Notably, a series of mechanistic studies appears to contradict a pathway involving enantioselective protonation of a Rh(I)–enolate, despite the fact that such a mechanism is invoked almost unanimously in the related addition of aryl boronic acids to methacrylate derivatives. Evidence suggests instead that migratory insertion or beta-hydride elimination is enantiodetermining and that isomerization of a Rh(I)–enolate to a Rh(I)–heterobenzyl species insulates the resultant α-stereocenter from epimerization. A bulky ligand, CTH-(R)-Xylyl-P-Phos, is crucial for reactivity and enantioselectivity, as it likely discourages undesired ligation of benzoxazole substrates or intermediates to on- or off-cycle rhodium complexes and attenuates coordination-promoted product epimerization.

The discovery of new catalytic reactions involving the use of abundant, inexpensive and sustainable metal complexes has enjoyed a resurgence of activities in recent years. This Cluster, Part I of a two-part series, focuses on new research findings from several prominent research groups, highlighting the rich diversities of new chemistry that can be originated from the use of sustainable metals in catalytic reactions.