Strain-Release-/Aromaticity-Driven Radical Generation and SO2-Capture Enables Acrylamides Bisfunctionalization via Photoredox Catalysis: Synthesis of S(VI) Functionalized Oxindoles

γ-keto sulfones, despite being a medicinally relevant building block, have not been integrated with the bioactive oxindole scaffold present in several alkaloid natural products. On the other hand, synthetic strategies involving SO2 fixation in organic molecules to access value-added products are gaining momentum from a green chemistry perspective. Therefore, the present report discloses a strategy en route to γ-keto alkylsulfonylated oxindoles bearing a β-all-carbon quarternary center. Toward this goal, the bisfunctionalization of N-(hetero)arylacrylamides has been realized via the strain-release driven ring-scission of strained 3°-cyclopropanols in the presence of DABSO under visible-light photoredox catalysis to access a library of γ-keto alkylsulfonylated oxindoles in moderate to good yields. Also, the aromaticity-driven bond-scission in pro-aromatics like 4-alkyl-1,4-DHPs in the presence of Na2S2O5 under visible-light photoredox catalysis have been exploited to trigger the alkylsulfonylative-arylation of N-(hetero)arylacrylamides to access a library of alkylsulfonylated oxindoles featuring a β-all-carbon quarternary center. The efficacy of the developed reactions has been tested through broad substrate-scope studies, and the mechanistic probing studies have been complimented with the DFT calculations to defend the mechanistic proposal.