Synthesis of (Enantioenriched) Dibenzyl Thioethers and Disulfides via S_N2 Nucleophilic Substitution of Quaternary Ammonium Salts

Abstract

A synthetic protocol of dibenzyl thioethers and dibenzyl disulfides via S N 2 nucleophilic substitution of quaternary ammonium salts and sodium sulfide nonahydrate and disodium disulfide under mild condition is described. In particular, if quaternary ammonium salts synthesized from enantiomerically enriched amines are adopted, highly enantioenriched dibenzyl thioethers (92-95% ee) with reverse configurations to their enantioenriched quaternary ammonium salts are obtained.Thioethers and organic disulfides extensively exist in glycoproteins, [1] fungal metabolites [2] and various plants of the genus Allium, [3] and exhibit some bioactivities. They have been widely used in medicinal chemistry, [1][2][3][4][5] chiral ligands/catalysts and drugs. [6] Dibenzyl disulfides containing S-S bond, which are commonly found in anti-cancer drugs. [2,4] A number of chiral thioether catalysts and ligands, such as A, B, C and D in Figure 1, have been used in a series of catalytically asymmetric reactions with excellent enantioselectivities. [6] Montelukast [7] and Cardizem [8] are typical chiral thioether medicines (Figure 1), which belong to the best-selling pharmaceutical products. Moreover, more than one-fifth of the top 200 most-prescribed drugs belong to sulfur-containing compounds, while thioethers represent the third most exemplified constituent of the sulfurcontaining drugs. [9] Chiral thioethers are converted into chiral sulfone compounds under the action of oxidant, which further broadens the application of chiral thioether compounds. [10] In the past decades, there are many methods for the preparation of thioethers, [11][12] but there are only a few approaches that prepare chiral thioethers from amine derivatives [13][14] via CÀ N cleavages. In particular, the exploration of organosulfur reagents for the construction of carbon-sulfur bonds is of widespread interest. [15,16] Tian and co-workers reported that stereospecifific nucleophilic substitution of higher reactive enantioenriched quaternary ammonium salts with a Nphenyl group from enantioenriched tertiary benzylic amines via in situ activation with benzyne (Scheme 1, eqn. (a)); [17] it is no reaction for less reactive benzylic quaternary ammonium salts with a N,N,N-trimethyl group. [17] Our group discovered that less reactive enantioenriched quaternary ammonium salts with a N,N,N-trimethyl group from enantioenriched tertiary benzylic amines via in situ activation with methyl triflate may be transformed into chiral benzylic thioethers via copper(I)-catalyzed CÀ S coupling reaction (Scheme 1, eqn. (b)). [18] Later, we further[a] Q. Tang, F.

Development of a Trimethylamine-Catalyzed Novel Synthesis of Azoxystrobin

“…Based on the above mechanistic studies, DFT calculations, and relevant literature, , a plausible mechanism for the TMA-catalyzed nucleophilic aromatic substitution is proposed in Scheme . Activated by the TMA catalyst, compound 3 could be in situ assembled into a highly active quaternary ammonium salt Int-I , which can accelerate the S N Ar reaction with 2-cyanophenol to generate the final product Azoxystrobin and the TMA catalyst, facilitating the next catalytic cycle.…”

Commercial Anion Exchange Membranes (AEMs) for Fuel Cell and Water Electrolyzer Applications: Performance, Durability, and Materials Advancement

“…This susceptibility arises from the nature of the quaternary ammonium structure, which contains active hydrogen atoms that can undergo reactions with hydroxide ions. During operation, OH − ions can attack the quaternary ammonium groups through processes such as Hofmann elimination and nucleophilic substitution reactions [109][110][111][112][113]. These reactions result in the degradation of the AEM, leading to a decrease in its performance and durability over extended periods of use.…”