Sulfur-controlled and rhodium-catalyzed formal (3 + 3) transannulation of thioacyl carbenes with alk-2-enals and mechanistic insights

Nonsilyl Bicyclic Secondary Amine Catalysts for the Asymmetric Transfer Hydrogenation of α,β-Unsaturated Aldehydes

The first chiral synthesis of nonsilyl bicyclic secondary amine organocatalysts and their application to the asymmetric transfer hydrogenation of α,β-unsaturated aldehydes are disclosed. A lower catalytic loading (5 mol %) is demonstrated for the reduction of a wide range of α,β-unsaturated aldehydes (up to 97% yield and up to 99% ee). The application of this scalable methodology is showcased for the asymmetric synthesis of bioactive molecules such as phenoxanol, citronellol, ramelteon, and terikalant.

Catalytic Diastereospecific and Enantioselective (3 + 2) Transannulations of 1,2,3-Thiadiazoles with Strained Norbornene Derivatives

With the adoption of a ring-strain-release strategy, iridium-catalyzed transannulations with norbornene derivatives are achieved in a diastereospecific and enantioselective manner. The first asymmetric transannulations of 1,2,3-thiadiazoles are reported.

Phenanthroline-imine ligands for iron-catalyzed alkene hydrosilylation

Iron-catalyzed organic reactions have been attracting increasing research interest but still have serious limitations on activity, selectivity, functional group tolerance, and stability relative to those of precious metal catalysts. Progress in this area will require two key developments: new ligands that can impart new reactivity to iron catalysts and elucidation of the mechanisms of iron catalysis. Herein, we report the development of novel 2-imino-9-aryl-1,10-phenanthrolinyl iron complexes that catalyze both anti-Markovnikov hydrosilylation of terminal alkenes and 1,2-anti-Markovnikov hydrosilylation of various conjugated dienes. Specifically, we achieved the first examples of highly 1,2-anti-Markovnikov hydrosilylation reactions of aryl-substituted 1,3-dienes and 1,1-dialkyl 1,3-dienes with these newly developed iron catalysts. Mechanistic studies suggest that the reactions may involve an Fe(0)–Fe(ii) catalytic cycle and that the extremely crowded environment around the iron center hinders chelating coordination between the diene and the iron atom, thus driving migration of the hydride from the silane to the less-hindered, terminal end of the conjugated diene and ultimately leading to the observed 1,2-anti-Markovnikov selectivity. Our findings, which have expanded the types of iron catalysts available for hydrosilylation reactions and deepened our understanding of the mechanism of iron catalysis, may inspire the development of new iron catalysts and iron-catalyzed reactions.

Newly developed iron complexes bearing 2-imino-9-aryl-1,10-phenanthroline ligands were successfully used to catalyze hydrosilylation of terminal alkenes and conjugated dienes in high yields with excellent anti-Markovnikov selectivity.

Catalytic (3 + 2) umpolung annulations of α-thioacyl carbenes with aryl isothiocyanates

As masked S-electrophilic thia-1,3-dipoles, 1,2,3-thiadiazoles undergo denitrogenative (3 + 2) umpolung transannulations with aryl isothiocyanates, regio- and stereoselectively.

Catalyst-controlled switchable [4 + 1], [4 + 3] and [3 + 2] domino reactions of azadienes and MBH carbonates: diverse synthesis of benzothiophene fused derivatives

Catalyst-controlled switchable domino reactions between azadienes bearing a benzothiophene moiety and isatin-derived MBH carbonates were developed. The [4 + 1] annulation was triggered in the presence of DABCO, giving a variety of benzothiophene fused pyrrole derivatives, while the [4 + 3] annulation occurred when changing the catalyst to DMAP. Furthermore, the [3 + 2] annulation mode was observed with the use of catalytic Ph₂PMe. Additionally, the synthetic utility of these domino reactions was demonstrated by gram-scale experiments and simple transformations of the products. To the best of our knowledge, catalyst-controlled synthesis of benzothiophene fused or spiro derivatives has rarely been reported.

Dual roles of bisphosphines and epoxides: Rh-catalyzed highly chemoselective and diastereoselective (3 + 2) transannulations of 1,2,3-thiadiazoles with cyanoepoxides

Dual roles of bisphosphines and epoxides are demonstrated in highly chemoselective and diastereoselective (3 + 2) transannulations.