S,C-Sulfonium Ylides from Thiophenes: Potential Carbene Precursors

Selenonium ylides: synthesis, characterization, and applications to photo-induced cyclopropanation reactions

Carbenes are important and highly reactive intermediates for the synthesis of various complex molecules. They are now an indispensable chemical species in organic chemistry and are used frequently to synthesize complex compounds in drug discovery chemistry. In general, carbenes are synthesized by a combination of transition metal catalysts and diazo compounds or by the decomposition reactions of diazo compounds. This paper reports the development of the visible light for the photochemical generation of carbenes from a novel C,Se-selenonium ylide. Overall, this photochemical carbene generation method using C,Se-selenonium ylide does not require a catalyst, is simple to perform, and enables highly efficient cyclopropanation reactions with alkenes.

Photocatalytic selective 1,2-hydroxyacylmethylation of 1,3-dienes with sulfur ylides as source of alkyl radicals

Exploration of the zwitterionic property of sulfur ylides has long been known as a flexible strategy in a wide range of chemical transformations for different ring-sized construction. By contrast, their...

Two-step Two-intermediate Photorelease Bolm-McCulla Reaction: Dual Release of Nitrene and Atomic Oxygen Reactive Intermediates

This article is a highlight of the paper by Isor et al. in this issue of Photochemistry and Photobiology. It describes the photolysis of a dibenzothiophene sulfoximine (bearing N-phenyl imino and S-oxide groups) to produce two reactive intermediates in tandem. The sulfoximine undergoes a S-N and S-O photocleavage to release phenyl nitrene and atomic oxygen [O(³ P)]. The phenyl nitrene dimerizes to azobenzene or is trapped by diethylamine to reach an azepine. From there, atomic oxygen arises in a secondary photolysis of dibenzothiophene sulfoxide. A computational analysis also reveals that the S-N bond is labile for initial nitrene release, with the secondary release of atomic oxygen by S-O cleavage. Whether future sulfoximine scaffolds can produce the reverse order release of O(³ P) then nitrene, or release both simultaneously, is yet to be established. Nonetheless, molecules with dual-intermediate release, such as coupled photoaffinity labeling and cellular oxidation, are worth pursuing.

Visible-Light-Promoted Polysubstituted Olefins Synthesis Involving Sulfur Ylides as Carbene Trapping Reagents

A blue-light-emitting diode (LED) promoted coupling of aryl diazoacetates with sulfur ylides is described. This protocol features mild conditions, good functional group tolerance, and broad substrate scope for both aryl diazoacetates with sulfur ylides. Under optimal reaction conditions, a wide range of trisubstituted olefins is obtained in moderate to good yield, which can be further transferred to other biologically important heterocycles after a two-step simple operation.

One-pot sequential synthesis of tetrasubstituted thiophenes via sulfur ylide-like intermediates

Herein, we describe a novel approach for the practical synthesis of tetrasubstituted thiophenes 8. The developed method was particularly used for the facile preparation of thienyl heterocycles 8. The mechanism for this reaction is based on the formation of a sulfur ylide-like intermediate. It was clearly suggested by (i) the intramolecular cyclization of ketene N,S-acetals 7 to the corresponding thiophenes 8, (ii) 1H NMR studies of Meldrum's acid-substituted aminothioacetals 9, and (iii) substitution studies of the methoxy group on Meldrum's acid containing N,S-acetals 9b. Notably, in terms of structural effects on the reactivity and stability of sulfur ylide-like intermediates, 2-pyridyl substituted compound 7a exhibited superior properties over those of others.

Beyond sulfide-centric catalysis: recent advances in the catalytic cyclization reactions of sulfur ylides

This Tutorial Review highlighted recent achievements on the catalytic cyclization reactions of sulfur ylide reagents, especially the asymmetric processes avoiding the use of structurally complex chiral sulfides.

Visible-Light-Driven Photocatalytic Activation of Inert Sulfur Ylides for 3-Acyl Oxindole Synthesis

Bicarbonyl-substituted sulfur ylide is a useful, but inert reagent in organic synthesis. Usually, harsh reaction conditions are required for its transformation. For the first time, it was demonstrated that a new, visible-light photoredox catalytic annulation of sulfur ylides under extremely mild conditions, permits the synthesis of oxindole derivatives in high selectivities and efficiencies. The key to its success is the photocatalytic single-electron-transfer (SET) oxidation of the inert amide and acyl-stabilized sulfur ylides to reactive radical cations, which easily proceeds with intramolecular C-H functionalization to give the final products.

Regioselective functionalisation of dibenzothiophenes through gold-catalysed intermolecular alkyne oxyarylation

A protocol has been developed for direct Csp(3)-Csp(2) bond formation at the 4- and 6-positions of dibenzothiophenes using a gold(I) catalyst with terminal alkynes and dibenzothiophene-S-oxides. The sulfoxide acts as a traceless directing group to avoid the need to prefunctionalise at carbon. The iterative use of this protocol is possible and has been employed in the preparation of novel macrocyclic structures. In addition, a cascade process shows how oxyarylations can be combined with other processes resulting in complex, highly efficient transformations.

Computational investigation of the photochemical deoxygenation of thiophene-S-oxide and selenophene-Se-oxide

A multireference CASSCF investigation of the dissociation of thiophene-S-oxide and selenophene-Se-oxide in their ground and accessible excited state demonstrates that dissociation can occur from T₂ with little or no barrier.