Two Novel Domino Reactions Triggered by Thiyl-Radical Addition to Vinylcyclopropyl Oxime Ether

Oxidative cross-coupling of thiols for S-X (X = S, N, O, P, and C) bond formation: mechanistic aspects

This review focuses on the reactive intermediates (disulfides, sulfenyl halides, thiyl radicals, sulfenium cations, and metal-organosulfur species) and the mechanisms of the recently reported oxidative couplings of thiols. These intermediates are generated by chemical oxidants, transition metal catalysts, electrochemistry, and photochemistry. Chemical oxidant-mediated reactions involve radical, halogenated, or cationic intermediates, or disulfides. Transition metal-catalyzed mechanisms proposed various metal-organosulfur intermediates to elucidate the reactivity and selectivity of metal catalysts. In electro- and photooxidation, direct oxidation/reduction mechanisms of reactants at the electrode or indirect oxidation/reduction of reactants in the presence of redox catalysts have been reported. The following sections are based on the products, thiosulfonates (S-S bond), sulfenamides, sulfinamides, and sulfonamides (S-N bond), sulfinates (S-O bond), thiophosphine oxides and thiophosphates (S-P bond), and sulfides, sulfoxides, and sulfones (S-C bond) and discuss the reaction mechanisms and the above-mentioned key intermediates for product formation. The contents of this review will provide helpful information, guiding the choice of oxidative coupling conditions for the synthesis of various organosulfur compounds with high yields and selectivity.

Kinetic Analysis of a Cysteine-Derived Thiyl-Catalyzed Asymmetric Vinylcyclopropane Cycloaddition Reflects Numerous Attractive Noncovalent Interactions

Kinetic studies of a vinylcyclopropane (VCP) cycloaddition, catalyzed by peptide-based thiyl radicals, are described. Reactions were analyzed by using reaction progress kinetic analysis, revealing that ring-opening of the VCP is both rate- and enantio-determining. These conclusions are further corroborated by studies involving racemic and enantiopure VCP starting material. Noncovalent interactions play key roles throughout: both the peptide catalyst and VCP exhibit unproductive self-aggregation, which appears to be disrupted by binding between the catalyst and VCP. This in turn explains the requirement for the key catalyst feature, a substituent at the 4-position of the proline residue, which is required for both turnover/rate and selectivity.

Auto-oxidative hydroxysulfenylation of alkenes

One-pot auto-oxidation mediated hydroxysulfenylation of electron-deficient and electron-rich olefins with phenthiols was explored.

Brønsted acid-catalyzed chemodivergent reactions of ortho-mercaptobenzyl alcohols with 3-alkyl-2-vinylindoles and styrenes: [5+2] cyclization versus hydroxysulfenylation

The title reactions were established to provide efficient methods for constructing a benzoxathiepine scaffold and synthesizing β-hydroxy sulfides in good yield and excellent diastereoselectivity.

Convenient Ambient Temperature Generation of Sulfonyl Radicals

Presented herein is a novel method for the efficient, ambient temperature generation of sulfonyl radicals from aryl and alkyl sulfonylbromides upon autoxidation of triethylborane (Et3B). The resultant radicals were regioselectively trapped via addition to terminal alkynes, generating a secondary vinyl radical that selectively abstracts a Br atom from RSO2Br, yielding the (E)-bromo vinylsulfones. Sensitivity towards Lewis basic groups was observed, presumably due to the disruptive coordination to Et3B before atom-transfer.