Paracyclophane-based Silver Phosphates as Catalysts for Enantioselective Cycloisomerization/Addition Reactions: Synthesis of Bicyclic Furans

Facile synthesis of N-(α-furanyl) alkyl sulfoximines via gold catalyzed Michael addition/cyclization of enynones and sulfoximines

Herein, we prepare a new array of N-(α-furanyl) alkyl sulfoximines via a gold catalyzed reaction of enynone with sulfoximine in moderate to very good yields. The reaction involves Michael addition of sulfoximine to enynone, followed by intramolecular cyclization. The presence of two chiral centres led to the formation of a mixture of diastereomers approximately in a 1 : 1 ratio. The salient features of the protocol include broad substrate scope, high efficiency and high yields. The synthetic utility of the protocol is explored using Suzuki-Miyaura cross-coupling and mild, metal-free opening of the furan ring.

H-Bonded Counterion-Directed Catalysis: Enantioselective Gold(I)-Catalyzed Addition to 2-Alkynyl Enones as a Case Study

H-bonded counterion-directed catalysis (HCDC) is a strategy wherein a chiral anion that is hydrogen-bonded to the achiral ligand of a metal complex is responsible for enantioinduction. In this article we present the application of H-bonded counterion-directed catalysis to the Au(I)-catalyzed enantioselective tandem cycloisomerization-addition reaction of 2-alkynyl enones. Following the addition of C-, N- or O-centered nucleophiles, bicyclic furans were obtained in moderate to excellent yield and enantioselectivity (28 examples, 59-96 % yield, 62 : 38 to 95 : 5 er). The optimal catalytic system, comprising a phosphinosquaramide Au(I) chloride complex and a BINOL-derived phosphoramidate Ag(I) salt, was selected in a combinatorial fashion from a larger library with the help of high-throughput screening. An enantioselectivity switch of ca. 120 Δee% was observed upon addition of the achiral Au(I) component to the Ag(I) salt.

H-Bonded Counterion-Directed Enantioselective Au(I) Catalysis

A new strategy for enantioselective transition-metal catalysis is presented, wherein a H-bond donor placed on the ligand of a cationic complex allows precise positioning of the chiral counteranion responsible for asymmetric induction. The successful implementation of this paradigm is demonstrated in 5-exo-dig and 6-endo-dig cyclizations of 1,6-enynes, combining an achiral phosphinourea Au(I) chloride complex with a BINOL-derived phosphoramidate Ag(I) salt and thus allowing the first general use of chiral anions in Au(I)-catalyzed reactions of challenging alkyne substrates. Experiments with modified complexes and anions, ¹H NMR titrations, kinetic data, and studies of solvent and nonlinear effects substantiate the key H-bonding interaction at the heart of the catalytic system. This conceptually novel approach, which lies at the intersection of metal catalysis, H-bond organocatalysis, and asymmetric counterion-directed catalysis, provides a blueprint for the development of supramolecularly assembled chiral ligands for metal complexes.

The Use of Domino Reactions for the Synthesis of Chiral Rings

This short review highlights the recent developments reported in the last four years on the asymmetric construction of chiral rings based on enantioselective domino reactions promoted by chiral metal catalysts.

1 Introduction

2 Formation of One Ring Containing One Nitrogen Atom

3 Formation of One Ring Containing One Oxygen/Sulfur Atom

4 Formation of One Ring Containing Several Heterocyclic Atoms

5 Formation of One Carbon Ring

6 Formation of Two Rings

7 Conclusion

2-Activated 1,3-enynes in enantioselective synthesis

The rapid enantioselective synthesis of valuable building blocks and pharmaceutically important compounds from easily accessible precursors is one of the major areas of focus in organic chemistry. In this context, 2-activated 1,3-enyne has emerged as a powerful synthon in recent years for the efficient synthesis of enantioenriched furans, allenes, 4-H-pyrans, and 4-isoxazolines, which are privileged scaffolds in bioactive compounds and natural products. This review will cover the history of the development of 2-activated 1,3-enyne in enantioselective synthesis along with the corresponding mechanisms, which may motivate further development in this area to forge more complex and valuable molecules.