A mild and practical method for the preparation of disulfides through visible-light-induced photocatalytic aerobic oxidation of thiols has been developed. The method involves the use of TiO2 as a heterogeneous photocatalyst. The catalyst's high stability and recyclability makes this method highly practical. The reaction can be substantially accelerated in a continuous-flow packed-bed reactor, which enables a safe and reliable scale-up of the reaction conditions. The batch and flow protocol described herein can be applied to a diverse set of thiol substrates for the preparation of homo- and hetero-dimerized disulfides. Furthermore, biocompatible reaction conditions (i.e., room temperature, visible light, neutral buffer solution, and no additional base) have been developed, which permits the rapid and chemoselective modification of densely functionalized peptide substrates without recourse to complex purification steps.
An organocatalytic aldehyde C-H bond arylation process for the synthesis of complex heteroaryl ketones has been developed. By exploiting the inherent electrophilicity of diaryliodonium salts, we have found that a commercial N-heterocyclic carbene catalyst promotes the union of heteroaryl aldehydes and these heteroaromatic electrophile equivalents in good yields. This straightforward catalytic protocol offers access to ketones bearing a diverse array of arene and heteroarene substituents that can subsequently be converted into molecules displaying structural motifs commonly found in medicinal agents.
We report the utilization of a novel catalyst for cycloisomerizations. The novel catalyst system contains gold nanoparticles supported on Al-SBA15, which was prepared by the ball-milling process. We developed a greener methodology for synthesizing spiroindolines under heterogeneous conditions, using this novel class of supported gold nanoparticles in combination with microwave irradiation. The catalyst is highly reusable and selective. Cycloisomerization reaction yields ranged from good to excellent leading to the formation of two novel classes of six- and seven-membered heterocycles, which have been unprecedented so far. The selectivity of the catalyst towards the desired products is high and the reaction can be performed in ethanol as the solvent. A one-pot cascade reaction could be established commencing with the Ugi-reaction to ensure diversity
An organocatalytic quadruple domino reaction initiated by a Friedel-Crafts-type reaction of electron-rich arenes is described. The procedure involving up to three different Michael acceptors afforded highly functionalized cyclohexenecarbaldehydes bearing an aniline moiety, which are of great pharmaceutical and agricultural interest. This diphenylprolinol trimethylsilyl ether-catalyzed reaction also generates up to 4 contiguous stereocenters. It could be shown that various functional groups are tolerated and all products were obtained with very good diastereo-and excellent enantioselectivity.
COMMUNICATIONSNico Erdmann et al. Figure 1. X-ray crystal structure of 19b.
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