Ti-Catalyzed Modular Ketone Synthesis from Carboxylic Derivatives and gem-Dihaloalkanes

Asymmetric Radical Cyclopropanation of α,β-Unsaturated Amides with α-Boryl and α-Silyl Dibromomethanes via Cr(II)-Based Metalloradical Catalysis

Transition-metal-catalyzed asymmetric carbene-transfer reactions represent a powerful strategy for synthesizing chiral cyclopropanes. However, current methods predominantly rely on stabilized carbene-bearing α-π-conjugated groups, restricting access to less stabilized carbenes, such as α-silyl and α-boryl carbenes. Herein, we present an unprecedented Cr(II)-based metalloradical system for the asymmetric cyclopropanation of α,β-unsaturated amides with α-boryl and α-silyl dibromomethanes in the presence of Mn as the reducing agent. Employing a chiral chromium complex, the reaction proceeds under mild conditions, yielding cyclopropanes with three contiguous stereocenters in high diastereo- and enantioselectivities. This method features a Cr-catalyzed radical-based stepwise cyclopropanation mechanism. The broad substrate scope, encompassing various α,β-unsaturated amides, demonstrates the protocol's versatility and robustness. Mechanistic insights, supported by experimental and computational studies, suggest the formation of α-Cr(III)-alkyl radical intermediates, delineating a pathway distinct from that of classical concerted cyclopropanations. This approach provides a powerful tool for synthesizing highly functionalized cyclopropanes, offering high potential for applications in drug discovery and development.

Metallaphotoredox Enabled Single Carbon Atom Insertion into Alkenes for Allene Synthesis

Efficient methods for synthesizing allenes from readily available starting materials pose a persistent challenge in organic chemistry. In this work, we present a novel two-stage protocol for allene synthesis involving the single-atom insertion into alkenes, facilitated by synergistic photoredox and cobalt catalysis. Diverging from conventional methods such as the Doering-LaFlamme reaction, this photochemical rearrangement approach operates efficiently under mild conditions in a radical-based manner. The protocol exhibits a broad substrate scope and demonstrates applicability in the late-stage diversification of alkene-containing natural products and bioactive molecules. Preliminary mechanistic studies and density functional theory (DFT) calculations offer insights into the reaction pathway, indicating a radical mechanism involving fleeting cyclopropyl carbene intermediates followed by rapid ring opening to form allenes.

Light-Driven Photocatalyst-Free Synthesis of β, δ-Functionalized Ketones from Aldehydes

The synthesis of ketones has been a long focus of chemistry research, on account of its unique reactivity. Herein, we report a simple light-driven photocatalyst-free synthesis of β, δ-functionalized ketones from aldehydes, using inexpensive and commercially abundant feedstock chemicals. This reaction is enabled by the direct acyl radical generation via hydrogen atom transfer and the subsequent radical addition process, avoiding the need for prefunctionalized substrates and organometallic reagent.

Rapid and Practical Synthesis of gem-Dibromoalkanes from Aldehydes by Tribromide Reagent

gem-Dibromoalkanes are important synthetic building block in organic chemistry, but their preparation is still troublesome. Herein, we have developed a simple and practical protocol for the synthesis of gem-dibromoalkanes from aldehydes using tetrabutylammonium tribromide and triphenyl phosphite. A variety of alkyl and aromatic aldehydes can be transformed into the corresponding products within 10 minutes. This protocol is also applicable to alcohols, and the configuration of chiral alcohol is inverted during the process with excellent enantiopurity.