Enantioselective Rhodium‐Catalyzed Coupling of Arylboronic Acids, 1,3‐Enynes,and Imines by Alkenyl‐to‐Allyl 1,4‐Rhodium(I) Migration

A chiral rhodium complex catalyzes the highly enantioselective coupling of arylboronic acids, 1,3‐enynes, and imines to give homoallylic sulfamates. The key step is the generation of allylrhodium(I) species by alkenyl‐to‐allyl 1,4‐rhodium(I) migration.     

N‐Heterocyclic‐Carbene‐Catalyzed Umpolung of Imines

N‐Heterocyclic carbene (NHC) catalysis has been widely used for the umpolung of aldehydes, and recently for the umpolung of Michael acceptors. Described herein is the umpolung of aldimines catalyzed by NHCs, and the reaction likely proceeds via aza‐Breslow intermediates. The NHC‐catalyzed intramolecular cyclization of aldimines bearing a Michael acceptor resulted in the formation of biologically important 2‐(hetero)aryl indole 3‐acetic‐acid derivatives in moderate to good yields. The carbene generated from the bicyclic triazolium salt was found to be efficient for this transformation.     

Collective Synthesis of Cladiellins Based on the Gold‐Catalyzed Cascade Reaction of 1,7‐Diynes

The cladiellin family of natural products, which includes molecules with various biological activities, continues to invite new synthetic studies. A gold‐catalyzed tandem reaction of 1,7‐diynes to construct the 6‐5‐bicyclic ring systems that are present in a number of natural products was developed. This reaction was applied as the key step to realize the formal and total syntheses of nine members of the cladiellin family in an enantio‐ and diastereoselective manner. This modular and efficient approach could also be used for the construction of other cladiellins, as well as their analogues, for follow‐up studies.     

Gold‐Catalyzed Stereocontrolled Synthesis of 2,3‐Bis(acetoxy)‐1,3‐dienes

Change the ligand, change the stereochemistry : 2,3‐Bis(acetoxy)‐1,3‐dienes are obtained in a stereocontrolled manner by a novel tandem 1,2‐/1,2‐bis(acetoxy) rearrangement (see scheme, R¹ and R² are δ⁺ stabilizing). Upon stabilization of the reaction intermediates, the ligand attached to gold controls the stereochemistry of the alkene in the second acetate migration, that is, N‐heterocyclic carbenes (NHC) favor cis alkenes, whereas phosphine ligands selectively afford trans olefins.

     

Highly Enantioselective Synthesis of Fused Tri‐ and Tetrasubstituted Aziridines: aza‐Darzens Reaction of Cyclic Imines with α‐Halogenated Ketones Catalyzed by Bifunctional Phosphonium Salt

The first enantioselective aza‐Darzens reaction of cyclic imines with α‐halogenated ketones was realized under mild reaction conditions by using amino‐acid‐derived bifunctional phosphonium salts as phase‐transfer promoters. A variety of structurally dense tri‐ and tetrasubstituted aziridine derivatives, containing benzofused heterocycles as well as spiro‐structures, were readily synthesized in high yields with excellent diastereo‐ and enantioselectivities (up to >20:1 d.r. and >99.9 % ee). The highly functionalized aziridine products could be easily transformed into different classes of biologically active compounds.     

Gold‐Catalyzed Cadiot–Chodkiewicz‐type Cross‐Coupling of Terminal Alkynes with Alkynyl Hypervalent Iodine Reagents: Highly Selective Synthesis of Unsymmetrical 1,3‐Diynes

A new and efficient method for the synthesis of unsymmetrical 1,3‐butadiynes by gold‐catalyzed C(sp)–C(sp) cross‐coupling of terminal alkynes with alkynyl hypervalent iodine(III) reagents has been developed. The reaction features high selectivity and efficiency, mild reaction conditions, wide substrate scope, and functional‐group compatibility, and is a highly attractive complement to existing methods. Mechanistic studies reveal that formation of a phenanthrolinyl‐ligated gold(I) complex is crucial for the efficiency and selectivity of the target transformation.