Atom-efficient arylation of N-tosylimines mediated by cooperative ZnAr2/Zn(C6F5)2 combinations.

By combining the Lewis acid Zn(C6F5)2 with nucleophilic diarylzinc (ZnAr2) reagents, we report the atom-efficient arylation of N-tosylimines under mild conditions. Mechanistic studies through the isolation of key intermediates reveal how the two zinc species act cooperatively to activate the imine substrate and regenerate the ZnAr2 reagent, enabling a limiting 50 mol% to be employed.

Merging Iridium-Catalyzed C-H Borylations with Palladium-Catalyzed Cross-Couplings Using Triorganoindium Reagents.

A versatile and efficient method to prepare borylated arenes furnished with alkyl, alkenyl, alkynyl, aryl, and heteroaryl functional groups is developed by merging Ir-catalyzed C-H borylations (CHB) with a chemoselective palladium-catalyzed cross-coupling of triorganoindium reagents (Sarandeses-Sestelo coupling) with aryl halides bearing a boronic ester substituent. Using triorganoindium cross-coupling reactions to introduce unsaturated moieties enables the synthesis of borylated arenes that would be difficult to access through the direct application of the CHB methodology. The sequential double catalyzed procedure can be also performed in one vessel.

Atom-efficient transition-metal-free arylation of N,O-acetals using diarylzinc reagents through Zn/Zn cooperativity.

Exploiting the cooperative action of Lewis acid Zn(C6F5)2 with diarylzinc reagents, the efficient arylation of N,O-acetals to access diarylmethylamines is reported. Reactions take place under mild reaction conditions without the need for transtion-metal catalysis. Mechanistic investigations have revealed that Zn(C6F5)2 not only acts as a Lewis acid activator, but also enables the regeneration of nucleophilic ZnAr2 species, allowing a limiting 50 mol% to be employed.

Main group bimetallic partnerships for cooperative catalysis.

Over the past decade s-block metal catalysis has undergone a transformation from being an esoteric curiosity to a well-established and consolidated field towards sustainable synthesis. Earth-abundant metals such as Ca, Mg, and Al have shown eye-opening catalytic performances in key catalytic processes such as hydrosilylation, hydroamination or alkene polymerization. In parallel to these studies, s-block mixed-metal reagents have also been attracting widespread interest from scientists. These bimetallic reagents effect many cornerstone organic transformations, often providing enhanced reactivities and better chemo- and regioselectivities than conventional monometallic reagents. Despite a significant number of synthetic advances to date, most efforts have focused primarily on stoichiometric transformations. Merging these two exciting areas of research, this Perspective Article provides an overview on the emerging concept of s/p-block cooperative catalysis. Showcasing recent contributions from several research groups across the world, the untapped potential that these systems can offer in catalytic transformations is discussed with special emphasis placed on how synergistic effects can operate and the special roles played by each metal in these transformations. Advancing the understanding of the ground rules of s-block cooperative catalysis, the application of these bimetalic systems in a critical selection of catalytic transformations encompassing hydroamination, cyclisation, hydroboration to C-C bond forming processes are presented as well as their uses in important polymerization reactions.

Transition-Metal-Free Oxidative Cross-Coupling of Triorganoindium Reagents with Tetrahydroisoquinolines.

Triorganoindium reagents (R3In) react with tetrahydroisoquinolines (THIQs) in the presence of Ph3CBF4 as an oxidant to afford 1-substituted THIQs. The reaction proceeds in good yields at rt using 50 mol % R3In with a variety of organic groups. 1H NMR studies show the generation of an iminium ion intermediate, supporting a two-step mechanism based on THIQ oxidation and R3In nucleophilic addition. This reaction was applied to the synthesis of the alkaloid nuciferine in three steps.

Synthesis of bench-stable solid triorganoindium reagents and reactivity in palladium-catalyzed cross-coupling reactions.

Bench-stable solid triorganoindium compounds have been prepared by coordination with 4-(dimethylamino)pyridine (DMAP). The solid R3In(DMAP) complexes are obtained from the corresponding solution of R3In in quantitative yield and can be stored for up to several weeks. These reagents show excellent reactivity in palladium-catalyzed cross-coupling reactions with organic electrophiles.

Transition-Metal-Free Cross-Coupling of Indium Organometallics with Chromene and Isochroman Acetals Mediated by BF3·OEt2.

A transition-metal-free coupling of triorganoindium reagents with benzopyranyl acetals mediated by a Lewis acid has been developed. The reaction of R3In with chromene and isochroman acetals in the presence of BF3·OEt2 afforded 2-substituted chromenes and 1-substituted isochromans, respectively, in good yields. The reactions proceed with a variety of triorganoindium reagents (aryl, heteroaryl, alkynyl, alkenyl, alkyl) using only 50 mol % of the organometallic, thus demonstrating the efficiency of these species. Preliminary mechanistic studies indicate the formation of an oxocarbenium ion intermediate in the presence of the Lewis acid.