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Abstract
An efficient Ag/pyridine co-mediated oxidative arylthiocyanation of activated alkenes via radical addition/cyclization cascade process was developed. This reaction could be carried out under mild conditions to provide biologically interesting 3-alkylthiocyanato-2-oxindoles in good to excellent yields. Mechanistic studies suggested a unique NCS• radical addition path and clarified the dual roles of catalytic pyridine as base and crucial ligand to accelerate the oxidation of Ag(I) to Ag(II), which is likely oxidant responsible for the formation of NCS• radical. These mechanistic results may impact the design and refinement of other radical based reactions proceeding through catalytic oxidations mediated by Ag(I)-pyridine/persulfate. The chemical versatility of thiocyanate moiety was also highlighted via SCN-tailoring chemistry in post-synthetic transformation for new S-C(sp3/sp2/sp), S-P, and S-S bonds constructions. The protocol provides an easy access to many important bioisosteres in medicinal chemistry and an array of sulfur-containing 2-oxindoles that are difficult to prepare by other approaches.
Highlights
Alkyl thiocyanates constitutes a key structural feature of a vast number of natural products and pharmaceuticals with a broad spectrum of biological activities (Figure 1)
The natural products psammaplin B, 9-thiocyanatopupukeanane, and fasicularin have been evaluated as a histone deacetylase (HDAC) enzyme inhibitor, antimicrobial agent, and cytotoxic agent, respectively [2,3,4]
The reported approaches for the preparation of alkyl thiocyanates mainly focused on the nucleophilic [10,11,12,13] and electrophilic [14,15,16] substitution of prefunctionalized alkyl substrates with appropriated thiocyanation reagent and the direct thiocyanation of alkyl C–H bonds via oxidative functionalization [17,18,19,20,21,22,23]
Summary
Alkyl thiocyanates constitutes a key structural feature of a vast number of natural products and pharmaceuticals with a broad spectrum of biological activities (Figure 1). Alkyl thiocyanates serve as safe cyanating agents and versatile synthetic intermediates for the assembly of functionalized heterocycles and sulfur-based compounds [5,6,7,8,9]. Their synthetic importance has prompted considerable interest in developing operative construction methodologies for this motif. In spite of Molecules 2018, 23, 2727; doi:10.3390/molecules23102727 www.mdpi.com/journal/molecules
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