Alkene Synthesis by Photo‐Wolff‐Kischner Reaction of Sulfur Ylides andN‐Tosylhydrazones

Abstract

A visible-light-driven and room temperature photo-Wolff-Kischner reaction of sulfur ylides and Ntosylhydrazones has been developed for the first time to provide modular access to alkene synthesis. The high functional group tolerance and broad substrate scope were demonstrated by more than 60 examples. Both E-and Zolefinic stereochemistry in the products could be controlled with excellent stereoselectivity. A series of mechanistic studies support that the reaction should proceed through a radical-carbanion crossover pathway, specifically involving addition of photo-generated sulfur ylide radical cations to N-tosylhydrazones to form carbanions and subsequent Wolff-Kischner process.Sulfur ylides, firstly reported in 1930 by Ingold and Jessop, [1] are a class of zwitterionic compounds characterized by a carbanion and a neighboring positively charged sulfur atom. Since the pioneering establishment of the synthetic prowess of these compounds in the Johnson-Corey-Chaykovsky epoxidation and cyclopropanation reactions, [2] the application of sulfur ylides as versatile one-carbon synthons in organic chemistry has undergone tremendous growth over the past decades, owing to their inherent unique chemical properties. [3] Many of these classical reactions have become textbook knowledge. Surprisingly, in sharp contrast to these ionic chemistry, the use of sulfur ylide radical cations, generated from the corresponding sulfur ylides by one-electron oxidation, in radical synthetic chemistry has been largely ignored. [4,5] The main reason may be attributed to the fact that the chemical properties of sulfur ylide radical cation depend primarily on the nature of the substituents on the sulfur, which often results in the formation of complex mixtures through various decomposition pathways. For example, Schuster was the first to investigate the reactivity modes of phenacyl sulfur ylides under photosensitization (λ > 400 nm) with 9,10-dicyanoanthracene (DCA) as the photocatalyst. [6] It was found that the outcome of the reactions depends remarkably on the structures of sulfur ylides because sulfur ylide radical cations were involved as the same intermediates (Scheme 1A). For instance, the DCA-sensitized photolysis of dimethylsulfur phenacylide (DMSY) led to formation of trans-[a] P.

Emerging Trends in N‐Tosylhydrazone Mediated Transition‐Metal‐Free Reactions

“…Chen and co‐workers [104] developed a unique method to synthesize highly stereoselective alkene 113 at room temperature in a pot fashion with photosensitizer catalyst Eosin Y reacting between sulfur ylide 112 and N ‐tosylhydrazone 3 in photo‐Wolff‐Kishner fashion using 40 W green LEDs as a light source. The importance of methodology is high due to tolerance of diversity of the functional groups and large scope of substrates with good yield and scalable up to gram level.…”

Visible light-promoted [3+2] cyclization reaction of vinyl azides with perfluoroalkyl-substituted-imidoyl sulfoxonium ylides

“…9 With the development of photochemistry, visible-light-induced photoredox carbon radical formation from sulfur ylides has been developed through SET-reduction and homolytic cleavage of C–S bonds in recent years. 10 However, to the best of our knowledge, the visible-light-induced radical-type reaction of vinyl azides with carbon radicals generated from the sulfur ylides has not been reported. While perfluoroalkyl-substituted imidoyl sulfoxonium ylides, a variant of sulfur ylides, have been widely applied as versatile perfluoroalkyl-containing synthons for the construction of various perfluoroalkyl-substituted heterocycles, 11 their synthetic potential in photochemical radical chemistry has not yet been explored.…”

Solvent-involved synthesis of pyrrolidin-5-one-2-carboxamides via a sequential Ugi/olefination reaction

“…1a). 4 The research groups of Aggarwal, 5 Tang, 6 Xiao, 7 Huang 8 and others 9 have disclosed many elegant reactions of sulfur ylides used to generate novel compounds. This traditional reactivity pattern utilizes sulfur ylides as intermediates to form various cyclic molecules through cycloaddition reactions.…”