Experimental and Computational Investigations into Trivalent Phosphorous-Mediated Radical Thiol Desulfurization

Radical-mediated thiol desulfurization processes using tricoordinate phosphorous reagents are used in a range of applications from small molecule synthesis to peptide modification. A combined experimental and computational examination of the mechanism and kinetics of the radical desulfurization of alkyl thiyl radicals using trivalent phosphorus reagents was performed. Primary alkyl thiols undergo desulfurization between 10^6 to 10^9 M-1s-1 depending on the phosphorus component with either an H-atom transfer step or β-fragmentation of the thiophosphoranyl intermediate may be rate-controlling. While the desulfurization of primary aliphatic thiols showed a marked dependence on the identity of phosphorous reagent used with either a rate-controlling H-atom transfer or -fragmentation, thiols yielding stabilized C-centered radicals showed much less sensitivity. Support for a stepwise S-atom transfer process progressing via a distorted trigonal bipyramidal thiophosphoranyl radical intermediate was obtained from DFT calculated energetics and hyperfine splitting values.

Light-Fuelled Dissipative Replication and Selection in Adaptive Biomimetic Chemical Networks

<p>Evolvability of the chemical replicator systems requires non-equilibrium energy dissipation, effective death pathways and transfer of structural information in the autocatalytic cycles. We engineered a chemical network with peptidic foldamer components, where UV light fuelled dissipative sequence-dependent exponential replication and replicator decomposition. The light-harvesting formation-recombination cycle of the thiyl radicals was coupled with the molecular recognition steps in the replication cycles. Thiyl radical-mediated chain reaction was responsible for the replicator death. The competing and kinetically asymmetric replication and decomposition processes led to light intensity-dependent selection and competitive exclusion. Dynamic adaptation to the energy input and the selection factor maximised the dissipation rate in the regime of exponential growth. The results contribute to the development of chemically evolvable replicator systems.</p>

Light-Fuelled Dissipative Replication and Selection in Adaptive Biomimetic Chemical Networks

<p>Evolvability of the chemical replicator systems requires non-equilibrium energy dissipation, effective death pathways and transfer of structural information in the autocatalytic cycles. We engineered a chemical network with peptidic foldamer components, where UV light fuelled dissipative sequence-dependent exponential replication and replicator decomposition. The light-harvesting formation-recombination cycle of the thiyl radicals was coupled with the molecular recognition steps in the replication cycles. Thiyl radical-mediated chain reaction was responsible for the replicator death. The competing and kinetically asymmetric replication and decomposition processes led to light intensity-dependent selection and competitive exclusion. Dynamic adaptation to the energy input and the selection factor maximised the dissipation rate in the regime of exponential growth. The results contribute to the development of chemically evolvable replicator systems.</p>

Solvent-Mediated Switching Between Oxidative Addition and Addition-Oxidation: Access to β-Hydroxysulfides and β-Arylsulfones by Addition of Thiols to Olefins in the Presence of Oxone

The reaction between aryl olefins and thiols in the presence of Oxone in toluene-water (9:1, v/v) affords β-hydroxy-2-arylethyl aryl sulfides smoothly by interception of the intermediary thiyl radicals with aryl...

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

This review describes the oxidative cross-couplings of thiols forming various organosulfur compounds, focusing on critical intermediates such as sulfenyl halides, thiyl radicals, sulfenium cations, disulfides, and organo-transition metal intermediates.

Recent Advances in the Synthesis of Sulfides, Sulfoxides and Sulfones via C-S Bond Construction from Non-Halide Substrates

The construction of a C-S bond is a powerful strategy for the synthesis of sulfur containing compounds including sulfides, sulfoxides, and sulfones. Recent methodological developments have revealed lots of novel protocols for C-S bond formation, providing easy access to sulfur containing compounds. Unlike traditional Ullmann typed C-S coupling reaction, the recently developed reactions frequently use non-halide compounds, such as diazo compounds and simple arenes/alkanes instead of aryl halides as substrates. On the other hand, novel C-S coupling reaction pathways involving thiyl radicals have emerged as an important strategy to construct C-S bonds. In this review, we focus on the recent advances on the synthesis of sulfides, sulfoxides, and sulfones from non-halide substrates involving C-S bond construction.

Thiyl Radicals: Versatile Reactive Intermediates for Cyclization of Unsaturated Substrates

Sulfur centered radicals are widely employed in chemical synthesis, in particular for alkene and alkyne hydrothiolation towards thioether bioconjugates. The steadfast radical chain process that enables efficient hydrothiolation has been explored in the context of cascade reactions to furnish complex molecular architectures. The use of thiyl radicals offers a much cheaper and less toxic alternative to the archetypal organotin-based radical methods. This review outlines the development of thiyl radicals as reactive intermediates for initiating carbocyclization cascades. Key developments in cascade cyclization methodology are presented and applications for natural product synthesis are discussed. The review provides a chronological account of the field, beginning in the early seventies up to very recent examples; a span of almost 50 years.

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

Disulfides are versatile catalysts. They can be photocatalysts, hydrogen atom transfer (HAT) catalysts, cocatalysts, or initiators in photocatalytic reactions. Under photoirradiation, organic disulfides can be easily cleaved into free thiyl radicals (RS•) and can reversibly add to unsaturated multiple bonds to catalyze a variety of functionalization reactions under mild conditions. In photoredox catalysis reactions, an excellent electron transfer ability and excellent radical properties also made these thiyl radicals powerful HAT catalysts. They have increasingly been proven useful in various types of organic photoreactions, such as cyclizations, anti-Markovnikov additions, aromatic olefin carbonylations, isomerizations, etc. They are a class of green, economic, mild, and chemoselective radical catalysts that deserve more attention. The present review highlights the recent progress in the field of disulfide-catalyzed and -cocatalyzed photocatalytic reactions for different reaction types.