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Catalysis with Selenium and Sulfur
Published in Andrew M. Harned, Nonnitrogenous Organocatalysis, 2017
The ability to introduce chirality on the sulfur atom is a defining feature of sulfinamide catalysts. In contrast, other sulfur-based organocatalysts relied on one or more stereocenters located on other atoms to induce enantioselectivity. Following their earlier work on N-sulfinyl urea catalysis,68 Ellman and coworkers recently expanded the reaction scope to cover the addition of cyclohexyl Meldrum’s acid 116 to nitroalkenes 115 using low catalyst loadings (0.2–3 mol%).69 The reaction catalyzed by N-sulfinyl urea 114 is shown in Scheme 5.28. In these reactions, the sulfinyl group functioned as a chiral directing group and as an electron-withdrawing substituent. More detailed investigation, however, revealed that the chirality of the diamine moiety of the catalyst did not have a major impact on the enantioselectivity—the N-sulfinyl group exerted the dominant stereocontrolling effect. This paved the way to the development of a N-sulfinyl catalyst 118 that is chiral solely at the sulfur atom and capable of promoting the addition of α-substituted Meldrum’s acids 120 to nitroalkenes 119 (Scheme 5.29).70 Other N-sulfinyl amide-catalyzed enantioselective reactions developed recently by the group include an intermolecular aldol reaction71 and addition of thioacetic acid to nitroalkenes.72
Direct synthesis of sulfinic esters via ultrasound accelerated tandem reaction of thiols and alcohols with N-bromosuccinimide
Published in Journal of Sulfur Chemistry, 2021
Lan-Anh Thi Nguyen, Tri-Nghia Le, Cong-Thang Duong, Chi-Tam Vo, Fritz Duus, Thi Xuan Thi Luu
Various indirect synthetic pathways of sulfinic acid esters from the sulfur(IV) derivatives have been performed via the nucleophilic substitution of alcohols/alkoxytrimethylsilane into sulfinyl chloride [8–13], sulfinamide [14–16], and sulfinyl sulfone [17]. Furthermore, the reaction of sulfinic acid with alcohols [18–20], the Brønsted/Lewis acid-catalyzed sulfination of alcohols by using sulfinic acid sodium salts [21–22], or by using p-toluenesulfonylmethyl isocyanide [23–25], the copper-catalyzed aerobic oxidative reaction [26,27], the esterification of sulfonyl hydrazides with alcohols promoted by NaHSO3 [28], the decomposition of N–sulfonylhydrazones mediated by Wittig ylide [29], or DIPEA (di-iso-propylethylamine) [30], as well as the in situ reduction of sulfonyl chlorides with alcohols in the presence of excess trimethyl phosphite have been also developed for the synthesis of sulfinic esters [31]. Recently, the alcoholysis of sulfinyl bromide in situ formed from the C-S(O) bond cleavage of sulfone-bearing t-butyl group by using N-bromosuccinimide was found out by Wei and co-workers [32]. Other popular pathways for the syntheses of sulfinic esters from the sulfur (II) derivatives, e.g. disulfides have attracted attention via the chlorination of disulfides in alcohols [33], and the oxidation of disulfides in alcohols by using N-bromosuccinimide [34], and lead tetraacetate [35]. Unfortunately, the sulfur (IV) derivatives are commercially available within limit, except for sulfinate salts. In addition, the sulfur (II) derivatives as disulfides are popularly prepared via the oxidative coupling of thiols by utilizing various oxidizing agents, e.g. N-bromosuccinimide [36].