Sulfur Ylides in Organic Synthesis and Transition Metal Catalysis

Extended Corey–Chaykovsky reactions: transformation of 2-hydroxychalcones to benzannulated 2,8-dioxabicyclo[3.2.1]octanes and 2,3-dihydrobenzofurans

We report the divergent synthesis of benzannulated 2,8-dioxabicyclo[3.2.1]octanes and 2,3-dihydrobenzofurans using the concept of extended Corey–Chaykovsky reactions.

Charge frustration in ligand design and functional group transfer

Molecules with different resonance structures of similar importance, such as heterocumulenes and mesoionics, are prominent in many applications of chemistry, including 'click chemistry', photochemistry, switching and sensing. In coordination chemistry, similar chameleonic/schizophrenic entities are referred to as ambidentate/ambiphilic or cooperative ligands. Examples of these had remained, for a long time, limited to a handful of archetypal compounds that were mere curiosities. In this Review, we describe ambiphilicity - or, rather, 'charge frustration' - as a general guiding principle for ligand design and functional group transfer. We first give a historical account of organic zwitterions and discuss their electronic structures and applications. Our discussion then focuses on zwitterionic ligands and their metal complexes, such as those of ylidic and redox-active ligands. Finally, we present new approaches to single-atom transfer using cumulated small molecules and outline emerging areas, such as bond activation and stable donor-acceptor ligand systems for reversible 1e^- chemistry or switching.

The crystal structure of 2-(2-(2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indol-2-ium-1-yl)phenoxy)acetate, C19H18N2O3

C19H18N2O3, monoclinic, P21/c (no. 14), a = 12.6187(7) Å, b = 9.4445(5) Å, c = 13.7424(8) Å, β = 99.248(5)°, V = 1616.49(16) Å3, Z = 4, R gt(F) = 0.0793, wR ref(F 2) = 0.2220, T = 100(10) K.

Synthetic Applications of Sulfonium Salts

This minireview aims to cover the developments over the past two decades in the chemistry of sulfonium salts. Specifically, insight is provided into the synthetic strategies available for the preparation of these compounds, the different reactivity patterns that are expected depending on their structural features or the reaction conditions applied, and the diversity of organic scaffolds that can thereby be synthesized. Additionally, the pros and cons derived from the use of sulfonium salts are presented and critically compared, when possible, in relation to reagents not based on sulfur but depicting similar reactivity.

The crystal structure of (E)-2-(((2-(1H-indol-3-yl)ethyl)iminio)methyl)-6-bromophenolate, C17H15N2BrO

C17H15N2BrO, monoclinic, P21/n (no. 14), a = 8.9886(8) Å, b = 8.2159(7) Å, c = 20.164(2) Å, β = 92.580(9)°, V = 1487.6(2) Å3, Z = 4, R gt(F) = 0.0370, wR ref(F 2) = 0.0716, T = 293(2) K.

Synthesis, Isolation and Crystal Structures of the Metalated Ylides [Cy3P-C-SO2Tol]M (M = Li, Na, K)

The preparation and isolation of the metalated ylides [Cy₃PCSO₂Tol]M (^Cy1‐M) (with M = Li, Na, K) are reported. In contrast to its triphenylphosphonium analogue the synthesis of ^Cy1‐M revealed to be less straight forward. Synthetic routes to the phosphonium salt precursor ^Cy1‐H₂ via different methods revealed to be unsuccessful or low‐yielding. However, nucleophilic attack of the ylide Cy₃P = CH₂ at toluenesulfonyl fluoride under basic conditions proved to be a high‐yielding method directly leading to the ylide ^Cy1‐H. Metalation to the yldiides was finally achieved with strong bases such as nBuLi, NaNH₂, or BnK. In the solid state, the lithium compound forms a tetrameric structure consisting of a (C–S–O–Li)₄ macrocycle, which incorporates an additional molecule of lithium iodide. The potassium compound forms a C₄‐symmetric structure with a (K₄O₄)₂ octahedral prism as central structural motif. Upon deprotonation the P–C–S linkage undergoes a remarkable contraction typical for metalated ylides.

Sulfur-Based Ylides in Transition-Metal-Catalysed Processes

Traditionally employed in the synthesis of small ring systems and rearrangement chemistry, sulfur-based ylides occupy a unique position in the toolbox of the synthetic organic chemist. In recent years a number of pioneering researchers have looked to expand the application of these unorthodox reagents through the use of transition metal catalysis. The strength and flexibility of such a combination have been shown to be of key importance in developing powerful novel methodologies. This chapter summarises recent developments in transition metal-catalysed sulfonium/sulfoxonium ylide reactions, as well as providing a historical perspective. In overviewing the successes in this area, the authors hope to encourage others into this growing field.