Raman spectroscopy, which is based on the inelastic scattering of photons by chemical entities, has been successfully utilized for the investigation of adsorbed molecules on surfaces, [1][2][3] although the low cross section limits its applications.Surface-enhanced Raman scattering (SERS) has drawn a lot of attention since its discovery in 1974, [4] primarily because it can greatly enhance the normally weak Raman signal and thereby facilitate the convenient identification of the vibrational signatures of molecules in chemical and biological systems. [5] Recently, the observation of single-molecule Raman scattering has further enhanced the Raman detection sensitivity limit and widened the scope of SERS for sensor applications. [6,7] Although SERS effects can be achieved simply by exploiting the electromagnetic resonance properties of roughened surfaces or nanoparticles of Au or Ag, the fabrication of reliable SERS substrates with uniformly high enhancement factors remains the focus of much research. Spraying Au or Ag colloids on a substrate leads to an extremely high SERS signal at some local 'hot-junctions'; [6][7][8] however, it is not easy to achieve a reliable, stable, and uniform SERS signal spanning a wide dynamical range using this method. Van Duyne and coworkers have used nanosphere lithography, [9] while Liu andLee exploited soft lithography, [10] in order to fabricate Ag nanoparticle arrays with high SERS activity and improved uniformity. Käll and co-workers have shown theoretically that the effective Raman cross section of a molecule placed between two metal nanoparticles can be enhanced by more than 12 orders of magnitude.[11] Such enhancement is likely to be related to the 'hot-junctions' observed in some SERS experiments. Several theoretical groups have also investigated field enhancement for SERS from metal nanoparticle arrays. [12][13][14] Specifically, García-Vidal and Pendry proposed that very localized plasmon modes, created by strong electromagnetic coupling between two adjacent metallic objects, dominate the SERS response in an array of nanostructures.[12] The interparticle-coupling-induced enhancement was attributed to the broadening of the plasmon resonance peak because the probability of the resonance covering both the excitation wavelength and the Raman peak increases with its width. They calculated the average enhancement factor over the surfaces of an array of infinitely long Ag nanorods with semicircular cross sections, and showed that significant near-field interaction occurs between adjacent nanorods when the gap between the nanorods reaches half the value of their diameter. Other groups have studied the dependence of the enhancement factor on the gap between adjacent nanoparticles on a SERS active substrate. For example, Gunnarsson et al. investigated SERS on ordered Ag nanoparticle arrays with an interparticle gap above 75 nm. [15] Lee and co-workers were able to achieve the temperature-controlled variation of interparticle gaps between Ag nanoparticles embedded in a polymer membra...

Sulfones are versatile intermediates in organic synthesis and important building blocks in the construction of biological active molecules or functional materials. This review provides a summary of recent developments in the synthesis of sulfones. 1 Introduction 2 Classical Methods and Variants 2.1 Oxidation of Sulfides 2.2 Aromatic Sulfonylation 2.3 Alkylation/Arylation of Sulfinates 2.4 Addition to Alkenes and Alkynes 2.5 Miscellaneous Methods 3 Metal-Catalyzed Coupling Reactions 4 Sulfone Synthesis by C-H Functionalization 5 Sulfur Dioxide Based Three-Component Approaches 6 Biological Synthesis of Sulfones 7 Conclusion

A photoredox‐catalyzed three‐component synthesis of N‐aminosulfonamides starting from diaryliodonium salts, hydrazines and sulfur dioxide is reported. This reaction proceeds under mild conditions at room temperature and is driven by visible light. A simple bisulfite salt can be used as a readily available and easy‐to‐handle sulfur dioxide source. Mechanistic studies support a catalytic photoredox pathway with the diaryliodonium salt as convenient source for aryl radicals.magnified image

Molecules containing a sulfonyl functionality, such as sulfones, sulfonyl chlorides or sulfonamides play an important role in organic chemistry and have found widespread application, especially in the construction of biologically active compounds. Recently, methods for the synthesis of the sulfonyl moiety utilizing sulfur dioxide as a key building block have received considerable attention. In this context, radical-based transformations with sulfur dioxide have emerged as a new and attractive approach for the construction of the sulfonyl functional group. This short review highlights recent advances in the use of sulfur dioxide in radical reactions and covers the historical background, which forms the basis for these current progresses. Limitations of the existing methods and potential further developments will be discussed.