Sulfonium ylide formation and subsequent C S bond cleavage of aromatic isopropyl sulfide catalyzed by hemin in aqueous solvent

Direct Observation of the Dynamics of Ylide Solvation by Hydrogen-bond Donors Using Time-Resolved Infrared Spectroscopy

The photoexcitation of α-diazocarbonyl compounds produces singlet carbene intermediates that react with nucleophilic solvent molecules to form ylides. The zwitterionic nature of these newly formed ylides induces rapid changes in their interactions with the surrounding solvent. Here, ultrafast time-resolved infrared absorption spectroscopy is used to study the ylide-forming reactions of singlet carbene intermediates from the 270 nm photoexcitation of ethyl diazoacetate in various solvents and the changes in the subsequent ylide-solvent interactions. The results provide direct spectroscopic observation of the competition between ylide formation and C-H insertion in reactions of the singlet carbene with nucleophilic solvent molecules. We further report the specific solvation dynamics of the tetrahydrofuran (THF)-derived ylide (with a characteristic IR absorption band at 1636 cm^-1) by various hydrogen-bond donors and the coordination by lithium cations. Hydrogen-bonded ylide bands shift to a lower wavenumber by -19 cm^-1 for interactions with ethanol, -14 cm^-1 for chloroform, -10 cm^-1 for dichloromethane, -9 cm^-1 for acetonitrile or cyclohexane, and -16 cm^-1 for Li⁺ coordination, allowing the time evolution of the ylide-solvent interactions to be tracked. The hydrogen-bonded ylide bands grow with rate coefficients that are close to the diffusional limit. We further characterize the specific interactions of ethanol with the THF-derived ylide using quantum chemical (MP2) calculations and DFT-based atom-centered density matrix propagation trajectories, which show preferential coordination to the α-carbonyl group. This coordination alters the hybridization character of the ylidic carbon atom, with the greatest change toward sp² character found for lithium-ion coordination.

Completion of the Set: Synthesis of the (6,X')-Flubromazepam Positional Isomers as Standards for Forensic Analysis

Mounting concern among forensic examiners regarding the emergence of positional isomers as technically legal alternatives to scheduled benzodiazepines has encouraged the preemptive synthesis of analogues as standards. Recently, flubromazepam was identified by the Drug Enforcement Administration for future scheduling, and subsequently, 9 of the 12 possible flubromazepam isomers were synthesized. However, the three (6,X')-isomers proved inaccessible via that approach. Herein, through a redesigned synthetic approach, the remaining three isomers were obtained, thus completing the set and enabling future forensic analysis.

Iron-promoted dealkylative carbene aminocyclization of δ-arylamino-α-diazoesters

Herein, we report a novel methodology to access N-aryl proline derivatives using amino-tethered α-diazoesters and cheap, readily available iron salts. Mechanistically, the aminocyclization reaction involves the initial formation of an iron-carbene complex followed by a nucleophilic attack of the aniline nitrogen atom to give an ammonium ylide intermediate, which finally undergoes the iron-promoted dealkylation.

Recent Perspectives on Rearrangement Reactions of Ylides via Carbene Transfer Reactions

Among the available methods to increase the molecular complexity, sigmatropic rearrangements occupy a distinct position in organic synthesis. Despite being known for over a century sigmatropic rearrangement reactions of ylides via carbene transfer reaction have only recently come of age. Most of the ylide mediated rearrangement processes involve rupture of a σ-bond and formation of a new bond between π-bond and negatively charged atom followed by simultaneous redistribution of π-electrons. This minireview describes the advances in this research area made in recent years, which now opens up metal-catalyzed enantioselective sigmatropic rearrangement reactions, metal-free photochemical rearrangement reactions and novel reaction pathways that can be accessed via ylide intermediates.

Sulfoxide Reduction/C(sp3)-S Metathesis Cascade in Ionic Liquid

A sulfoxide reduction/C-S bond metathesis cascade between sulfoxides and alkyl bromides has been developed to access high-value sulfides without the use of any catalysts or bases. In this cascade, classical Kornblum oxidation is employed to reduce sulfoxides with alkyl bromides in ionic liquid. This protocol features high functional tolerance, mild conditions, promising scalability, and sustainable solvents.

Solvent-dependent, rhodium catalysed rearrangement reactions of sulfur ylides

Depending on the solvent used, benzyl sulfides undergo in the presence of a rhodium(ii) catalyst either [1,2]- or [2,3]-sigmatropic rearrangement.