Early Main Group Metal L ewis Acid Catalysis

DFT Analysis into the Calcium(II)-Catalyzed Coupling of Alcohols With Vinylboronic Acids: Cooperativity of Two Different Lewis Acids and Counterion Effects

“…During the past decade, calcium-based Lewis acids have witnessed an upsurge in applications in homogeneous catalysis. This renaissance was mostly led by the group of Niggemann who reported that Ca­(NTf 2 ) 2 can be activated by an ammonium salt of a weakly coordinating anion such as n Bu 4 NPF 6 to give a highly oxophilic Lewis acid able to abstract hydroxy groups and promote cationic transformations. , This strategy is also efficient with Ca­(OTf) 2 . Other functional groups can also be activated, such as ketones or alkenes .…”

Direct Assembly of Phthalides via Calcium(II)-Catalyzed Cascade ortho-C-Alkenylation/Hydroacyloxylation of 3-Aminobenzoic Acids with Alkynes in Hexafluoroisopropanol

“…Very recently, alkaline-earth calcium-based Ca­(NTf 2 ) 2 has attracted much attention in the organic synthesis community for its C–C bond forming reactions due to its economical, nontoxic, and easy to handle properties. , Latest studies revealed that the combination of Ca­(NTf 2 ) 2 with hexafluoroisopropanol (HFIP) resulted in an active catalytic system, and the acidity of the corresponding system could be increased to trigger reactions that were unlikely to take place in traditional organic solvents . Such a strategy has been successfully applied to the alkylation of anilines with alkenes, which relies on a concerted-like mechanism that leads to excellent regioselectivity in favor of the streamlined formation of the ortho -product (Scheme a) .…”

Lewis Acid/Hexafluoroisopropanol: A Promoter System for Selective ortho-C-Alkylation of Anilines with Deactivated Styrene Derivatives and Unactivated Alkenes

“…At the outset, we examined the feasibility of this concept by investigating the inherent reactivity of highly deactivated 4-cyanostyrene 1a with diphenylamine 2a (4 equiv) in the presence of the promoter system that we previously described for hydrofunctionalizations: Ca­(NTf 2 ) 2 / n Bu 4 NPF 6 (20 mol %) in HFIP (0.2 M) (Table ). With respect to this system, the role of the ammonium salt of weakly coordinating hexafluorophosphate is to promote an anion metathesis to form the heteroleptic salt Ca­(NTf 2 )­(PF 6 ), which is more prone to activate the H-bond network of HFIP than the sole Ca­(NTf 2 ) 2 .…”