Radical functionalization of allenes

Allenes exhibit comparatively lower stability compared to alkenes and alkynes, which confers heightened reactivity to these compounds. Recently, the radical functionalization of allenes has progressed considerably, leading to a renaissance in the synthesis of functional natural products, drugs and their analogues, but summary work addressing this aspect has not been reported. This review systematically summarizes recent advancements in the field of radical functionalization of allenes reported within the past five years. It encompasses the difunctionalization and trifunctionalization of the three carbon atoms in allenes, as well as the functionalization of C-Y bonds (Y = H, Br). The representative studies are categorized based on the type of radicals generated, including C-, N-, O-, S-, and Se-centered radicals. For individual more complex reactions, the mechanisms are explored and briefly discussed.

Substituent-Dependent, Switchable Synthesis of Nonaromatic and Aromatic Heterocyclic Sulfones Using Visible Light

In this Letter, we described a visible-light-induced switchable synthesis of nonaromatic and aromatic sulfonyl heterocycles. The product selectivity between 2,5-dihydropyrrole and pyrrole can be tuned by altering the substituent on the N atom of 1,6-diyne. We highlight the intricacy and efficiency of this approach in constructing molecular frameworks under mild conditions with a high functional group tolerance. This study elucidates the mechanism underlying product selectivity, highlighting its potential as a compelling alternative to traditional synthetic techniques.

Metal- and base-free tandem sulfonylation/cyclization of 1,5-dienes with aryldiazonium salts via the insertion of sulfur dioxide

A metal- and base-free 5-endo-trig sulfonylative cyclization between 1,5-dienes, aryldiazonium salts and SO₂ (from SOgen) is presented. This method could successfully produce sulfonylated pyrrolin-2-ones in one pot with excellent regioselectivity and good-to-excellent yields. This strategy features mild reaction conditions and broad substrate scope. Moreover, a scale-up reaction and three synthetic applications demonstrate the practicality of this method. Lastly, control experiments indicate that the 5-endo-trig sulfonylative cyclization may proceed in a radical pathway.

A new metal- and base-free method for synthesizing sulfonylated pyrrolin-2-ones from 1,5-dienes, aryldiazonium salts and SO₂ is presented. This transformation features mild reaction conditions and broad substrate scope.

Visible-Light-Induced Tandem Reaction of Allenes with Selenesulfonates Leading to (E)-2,3-Disulfonylpropene Derivatives

A visible-light-induced tandem reaction of allenes with selenesulfonates was developed, providing (E)-2,3-disulfonylpropene derivatives in moderate to good yields. This reaction was featured with simple operation, good regioselectivity and stereoselectivity, and wide functional group tolerance. Photoinduced radical additions via energy transfer were proposed.