Metal‐Free Synthesis of β‐Bromoalkenyl Sulfides via Deoxygenative Bromination/Olefination/Sulfenylation of Ketones with Sulfonyl Hydrazides and Pyridinium Tribromide

Abstract

A novel metal-free method for synthesis of β-bromoalkenyl sulfides via deoxygenative bromination/olefination/sulfenylation process using commercially available ketones, sulfonyl hydrazides and pyridinium tribromide as starting materials has been developed. In this reaction, pyridinium tribromide plays the role of oxidant and substrate, wherein water and molecular nitrogen are generated as environmentally benign by-products. Preliminary investigation revealed that vinyl bromides were critical intermediate. Importantly, this protocol not only obviates the use of alkynes and traditional sulfenylating agents, but also reveals that ketones can be used as precursors of vinyl bromides.

Iodine‐Promoted Synthesis of 2‐Naphthyl Thioethers from Tetralones and Sulfonyl Hydrazides

“…According to the above experimental results and our previous reports, [9,10] a possible reaction mechanism for this deoxygenative olefination/sulfenylation/aromaticzation reaction is proposed in Scheme 6. Firstly, 1-tetralone 1 reacts with sulfonyl hydrazide 2 to afford sulfonylhydrazone 6, which is oxidized by iodine via single-electron transfer process.…”

“…Alternatively, sulfonyl hydrazide 2 reacts with iodine to yield sulfenyl iodide 9. [9] And then alkenyl iodide undergoes sulfenylation with sulfenyl iodide 9, deprotonation, [1,5]sigmatropic hydrogen shift, and elimination of HI to give 2naphthyl thioether 3. [9c] In summary, we have reported an iodine-promoted method for synthesis of 2-naphthyl thioethers from tetralones with sulfonyl hydrazides via tandem deoxygenative olefination/ sulfenylation/aromatization process.…”

“…As our efforts in exploring new chemistry of sulfonyl hydrazide, [9] recently, we have developed an efficient byproduct-catalyzed redox-neutral process of cyclic alkenyl iodides with sulfonyl hydrazides to give structurally diverse 2naphthyl thioethers in the absence of any external catalysts and additives. [9c] In contrast to many other traditional methods to synthesize 2-naphthyl thioethers, [10] this protocol is very simple, manipulative convenience and environmental friendliness.…”

Transition Metal‐Free Sulfenylation of C−H Bonds for C−S Bond Formation in Recent Years: Mechanistic Approach and Promising Future

“…In one way, it leads to a major product and on the other side, a minor product was formed along with bromine radical as side product (Scheme 93). [206] …”

“…Then, amine mediated demethylation occurs i. e., nucleophilic attack of triflate anion on methyl resulted into 1,4disulfanylarenes (297) and CF 3 COOMe (Scheme 92). [205] Bao and co-workers [206] reported a metal-free, pyridinium tribromide mediated synthesis of β-bromoalkenyl sulfides (299). The developed methodology was successfully applied to aryl alkyl ketone (298) and sulfonyl hydrazides (47) using a sequence of three reactions i. e., deoxygenative bromination, olefination and sulfenylation, where corresponding product were obtained in good yield with high E/Z selectivity.…”