Panda Niranjan, Palit Kuntal, Mohapatra Soumya
Department of Chemistry, National Institute of Technology, Rourkela, Odisha-769008, India.
Org Biomol Chem. 2024 Sep 11;22(35):7103-7110. doi: 10.1039/d4ob00740a.
Conventionally, carbenium and onium ions are prepared in the presence of nucleophiles due to their instability and transient nature. The nucleophiles that are unstable or inert to the reaction media cannot be used for reaction with the cationic species to access the desired compounds. To overcome these limitations, developing methods for generating organic cations irreversibly in the absence of nucleophiles is essential. The "cation pool" method developed by Yoshida and co-workers stands out as a reliable strategy to generate and accumulate the reactive cations in solution in the absence of nucleophiles. The cation pool method involves the electrolysis of the substrate in the absence of nucleophiles, usually at low temperature. Moreover, the generation of halogen and chalcogen cations through electrolysis needs extra care because of their low stability. This review covers our effort in generating and accumulating halogen cations as "cation pools", most importantly by simply heating a mixture of dimethyl sulfoxide (DMSO) and 1,2-dihaloethane (DXE, X = Cl, Br, I), and their use in the halogenation reactions. Furthermore, condition-dependent Pummerer-type fragmentations of DMSO-stabilized halogen cations to methyl(methylene)sulfonium ions and chlorodimethylsulfonium ions for synthetic applications are described.
传统上，由于碳正离子和鎓离子的不稳定性和瞬态性质，它们是在亲核试剂存在的情况下制备的。对反应介质不稳定或呈惰性的亲核试剂不能用于与阳离子物种反应以获得所需化合物。为克服这些限制，开发在无亲核试剂情况下不可逆地生成有机阳离子的方法至关重要。吉田及其同事开发的“阳离子池”方法是一种可靠的策略，可在无亲核试剂的情况下在溶液中生成并积累活性阳离子。阳离子池方法涉及在无亲核试剂的情况下，通常在低温下对底物进行电解。此外，由于卤族元素阳离子和硫族元素阳离子稳定性较低，通过电解生成它们时需要格外小心。本综述涵盖了我们在生成和积累卤族元素阳离子作为“阳离子池”方面所做的工作，最重要的是通过简单加热二甲亚砜（DMSO）和1,2 - 二卤乙烷（DXE，X = Cl、Br、I）的混合物来实现，以及它们在卤化反应中的应用。此外，还描述了DMSO稳定的卤族元素阳离子在合成应用中依赖条件的普默勒尔型碎片化反应生成甲基（亚甲基）锍离子和氯代二甲锍离子的过程。
