Catalyst-free selenylation/semipinacol rearrangement cascades of alkenyl cyclobutanols: synthesis of β-selenylated cyclopentanones

Electrochemical Radical Selenylation of Alkenes and Arenes via Se-Se Bond Activation

A novel electrochemical radical selenylation of alkenes and activated arenes without external oxidants is reported. The diselenide was fully transformed into Se-centered radicals through electrochemical Se-Se bond activation. Three-component radical carbonselenation was successfully realized using styrenes to trap the RSe radical. Besides, the direct coupling of RSe radicals with activated arenes was further developed. Using this atom-economic protocol, diversity of unsymmetric aryl-aryl, aryl-alkyl, and alkyl-alkyl selenoethers was obtained regioselectively, which has potential application in biological chemistry.

Recent development and applications of semipinacol rearrangement reactions

As has been well-recognized, semipinacol rearrangement functions as an exceptionally useful methodology in the synthesis of β-functionalized ketones, creation of quaternary carbon centers, and construction of challenging carbocycles. Due to their versatile utilities in organic synthesis, development of novel rearrangement reactions has been a vibrant topic that continues to shape the research field. Recent breakthroughs in novel electrophiles, tandem processes, and enantioselective catalytic transformations further enrich the toolbox of this chemistry and spur the strategic applications of this methodology in natural product synthesis. These achievements will be discussed in this minireview.

Small rings in the bigger picture: ring expansion of three- and four-membered rings to access larger all-carbon cyclic systems

The release of the inherent ring strain of cyclobutane and cyclopropane derivatives allows a rapid build-up of molecular complexity. This review highlights the state-of-the-art of the ring expansions of three- and four-membered cycles and is organised by types of reactions with emphasis on the reaction mechanisms. Selected examples are discussed to illustrate the synthetic potential of this elegant synthetic tool.