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Cyclopropanation of Alkenes with Dichloromethane and Chloroform via Halogen Atom Transfer Using Amine Carboxyborane

2026-02-10T09:10:20Z

Title: Cyclopropanation of Alkenes with Dichloromethane and Chloroform via Halogen Atom Transfer Using Amine Carboxyborane Author(s): Park, Changhee; Lee, Sunggi Abstract: Cyclopropanes are privileged motifs in medicinal chemistry due to their role as bioisosteres of arenes, alkenes, and small alkyl groups. Herein, we report a transition-metal-free, photoredox-catalyzed cyclopropanation of diverse alkenes via halogen atom transfer between dichloromethane (CH2Cl2) as a C1 synthon and amine-ligated boryl radicals generated from amine carboxyborane. This method proceeds under mild reaction conditions, exhibits a broad substrate scope, and is scalable. The synthetic utility is further highlighted by deuterium incorporation using CD2Cl2 and the formation of chlorocyclopropane products using chloroform (CHCl3) and CDCl3, enabling access to valuable chlorinated and isotopically labeled cyclopropanes.

Real-Time Visualisation of Reaction Kinetics and Dynamics: Single-Molecule Insights into the Iminium-Catalysed Diels-Alder Reaction

2025-12-18T02:40:54Z

Title: Real-Time Visualisation of Reaction Kinetics and Dynamics: Single-Molecule Insights into the Iminium-Catalysed Diels-Alder Reaction Author(s): Park, Minsoo; Ahn, Yongdeok; Cho, Juhyeong; Jang, Juhee; Lee, Wonhee John; Seo, Sangwon; Lee, Sunggi; Seo, Daeha Abstract: Investigation of the fundamental microscopic processes occurring in organic reactions is essential for optimising both organocatalysts and synthetic strategies. In this study, single-molecule fluorescence microscopy was employed to study the Diels-Alder reaction catalysed by a first-generation MacMillan catalyst, providing direct insights into its kinetic dynamics. This reaction proceeds via a series of reversible processes under equilibrium conditions (S -><- IM1 -><- IM2 -> P, IM1 and IM2: N,O-acetal and iminium ion intermediates, respectively). The individual reaction trajectories of single molecules were directly observed in real-time, and the kinetic transitions between the different states were quantitatively analysed using a hidden Markov model, thereby enabling precise determination of the kinetic rate constants and transition probabilities at the single-molecule level. In particular, the unique structural features of the MacMillan catalyst were probed to reveal how specific interactions stabilise the reaction intermediates and influence their kinetic behaviours. These findings highlight the importance of single-molecule fluorescence microscopy in understanding the fundamental mechanisms of organic reactions and guiding the rational design of more effective catalysts.

The Giese reaction of alkyl bromides using amine carboxyboranes

2025-07-25T02:43:22Z

Title: The Giese reaction of alkyl bromides using amine carboxyboranes Author(s): Park, Changhee; Gi, Seyun; Yoon, Seongkyeong; Kwon, Seong Jung; Lee, Sunggi Abstract: Amine carboxyborane enabled efficient halogen atom transfer (XAT) with 1 degrees, 2 degrees, and 3 degrees alkyl bromides, resulting in Giese addition products with various electron-deficient double bonds. Moreover, direct addition of several boryl radicals was also possible using several ligated carboxyboranes.

Controlling Reactivity through Spin Manipulation: Steric Bulkiness of Peroxocobalt(III) Complexes

2025-07-25T03:30:39Z

Title: Controlling Reactivity through Spin Manipulation: Steric Bulkiness of Peroxocobalt(III) Complexes Author(s): Kim, Seonghan; Lee, Yuri; Tripodi, Guilherme L.; Roithova, Jana; Lee, Sunggi; Cho, Jaeheung Abstract: The intrinsic relationship between spin states and reactivity in peroxocobalt(III) complexes was investigated, specifically focusing on the influence of steric modulation on supporting ligands. Together with the previously reported [CoIII(TBDAP)(O2)]+ (2Tb), which exhibits spin crossover characteristics, two peroxocobalt(III) complexes, [CoIII(MDAP)(O2)]+ (2Me) and [CoIII(ADDAP)(O2)]+ (2Ad), bearing pyridinophane ligands with distinct N-substituents such as methyl and adamantyl groups, were synthesized and characterized. By manipulating the steric bulkiness of the N-substituents, control of spin states in peroxocobalt(III) complexes was demonstrated through various physicochemical analyses. Notably, 2Ad oxidized the nitriles to generate hydroximatocobalt(III) complexes, while 2Me displayed an inability for such oxidation reactions. Furthermore, both 2Ad and 2Tb exhibited similarities in spectroscopic and geometric features, demonstrating spin crossover behavior between S = 0 and S = 1. The steric bulkiness of the adamantyl and tert-butyl group on the axial amines was attributed to inducing a weak ligand field on the cobalt(III) center. Thus, 2Ad and 2Tb are an S = 1 state under the reaction conditions. In contrast, the less bulky methyl group on the amines of 2Me resulted in an S = 0 state. The redox potential of the peroxocobalt(III) complexes was also influenced by the ligand field arising from the steric bulkiness of the N-substituents in the order of 2Me (−0.01 V) < 2Tb (0.29 V) = 2Ad (0.29 V). Theoretical calculations using DFT supported the experimental observations, providing insights into the electronic structure and emphasizing the importance of the spin state of peroxocobalt(III) complexes in nitrile activation. © 2024 American Chemical Society.