A metal‐free [2+2] cycloaddition and 1,4‐addition sequence induced by S‐centered radicals has been achieved by treating benzene‐linked allene‐ynes with aryldiazonium tetrafluoroborates and DABCO‐bis(sulfur dioxide) in a one‐pot procedure. The reaction provides a greener and more practical access to functionalized cyclobuta[a]naphthalen‐4‐ols with valuable applications. More than 50 examples are demonstrated with excellent diastereoselectivity and chemical yields. The reaction pathway is proposed to proceed by the following steps:[2+2] cycloaddition, insertion of SO2, 1,4‐addition, diazotization, and tautomerization.

A new visible‐light photocatalytic arylsulfonylation and bicyclization of C(sp3)‐tethered 1,7‐enynes with sulfinic acids has been developed, delivering functionalized sulfone‐containing benzo[a]fluoren‐5‐ones with generally good yields. This Eosin Y‐catalyzed approach makes use of visible light as a safe and eco‐friendly energy source to drive cascade cyclization reactions, resulting in continuous multiple bond‐forming events including C–S and C–C bonds to efficiently construct polycyclic‐linked alkyl aryl sulfones.magnified image

A new C-center radical-triggered bicyclization cascade of N-tethered 1,7-enynes for forming 28 examples of biologically interesting spirocyclohexadienone-containing cyclopenta[c]quinolin-4-ones with two all-carbon quaternary stereocenters has been established under mild conditions. The in situ generated diazonium salts from 4-methoxyanilines and t-BuONO are served as 4-methoxyphenyl precursors without additional oxidant, enabling 6-exo-dig cyclization/5-exo-trig ipso-cyclization to construct three new C-C bonds through metal-free dearomatization. The reaction also features broad substrate scope, annulation efficiency, and high functional group tolerance.

The combination of Co(acac)2 and AgOTf enables the bimetallic relay catalysis reaction of 2-ethynylanilines and isocyanides, allowing easy and low-cost access to new densely functionalized pyrrolo[2,3-b]indoles. The reaction pathway involves a Co(acac)2-catalyzed double isocyanide insertion followed by a silver-enabled 1,3-dipolar cycloaddition. The synthetic utility of these bicycloaddition reactions results in subsequent C-C and C-N bond-forming events to rapidly build up molecular complexity.

A new silver-mediated 5-exo-dig cyclization of 2-alkynylbenzonitriles with disubstituted phosphine oxide and HO has been developed. The reaction enables multiple bond-forming events including C-P, C-C and C-O bonds under atmospheric conditions, leading to the concise and direct formation of 28 examples of phosphorus-containing 1-indenones with generally good yields.