Chirality memory of α-methylene-π-allyl iridium species

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An efficient double allene protocol for the formation of benzazocines has been developed. The reaction constitutes a highly regioselective palladium‐catalyzed formal [6+2] annulation of allenyl benzoxazinanones with terminal allenes forming the challenging 8‐membered cycles. Decent yields and excellent regioselectivity have been observed under mild conditions with a remarkable Z‐stereoselectivity for the exo‐cyclic C=C bonds. The synthetic potentials of benzazocine products have been demonstrated.

Section: Methodsmentioning

confidence: 99%

Palladium‐Catalyzed [6+2] Double Allene Annulation for Benzazocines Synthesis

2022

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Nickel‐Catalyzed Enantioselective Synthesis of Dienyl Sulfoxide

Gao,

Wang,

Zhang

et al. 2023

Sulfoxides are widely used in the pharmaceutical industry and as ligands in asymmetric catalysis. However, the efficient asymmetric synthesis of this structural motif remains limited. In this study, we disclosed a Ni‐catalyzed enantioconvergent reaction that utilizes both racemic allenyl carbonates and β‐sulfinyl esters. Our method employs cheap and more sustainable Ni(II) as a precatalyst and successfully overcomes the challenging poisoning effect and instability of sulfenate generated in situ. This enables the synthesis of a series of dienyl sulfoxides with enantioselectivity of up to 98 % ee. The product exhibits tremendous potential in various applications, including diastereoselective Diels–Alder reactions, coordination with transition metals, and incorporation into medicinal compounds, among others. Using a combination of experimental and computational methods, we have uncovered an interesting associated outersphere mechanism that contrasts with conventional mechanisms commonly observed in asymmetric transition metal catalysis.

Nickel‐Catalyzed Enantioconvergent Allenylic Amination of Allenols Activated by Hydrogen‐Bonding Interaction with Methanol

Zhang,

Lin,

et al. 2024

The ubiquitous nature of amines in drug compounds, bioactive molecules and natural products has fueled intense interest in their synthesis. Herein, we introduce a nickel‐catalyzed enantioconvergent allenylic amination of methanol‐activated allenols. This protocol affords a diverse array of functionalized allenylic amines in high yields and with excellent enantioselectivities. The synthetic potential of this method is demonstrated by employing bioactive amines as nucleophiles and conducting gram‐scale reactions. Furthermore, mechanistic investigations and DFT calculations elucidate the role of methanol as an activator in the nickel‐catalyzed reaction, facilitating the oxidative addition of the C–O bond of allenols through hydrogen‐bonding interactions. The remarkable outcomes arise from a rapid racemization of allenols enabled by the nickel catalyst and from highly enantioselective dynamic kinetic asymmetric transformation of η3‐alkadienylnickel intermediates.