Visible-light Photocatalytic Aerobic Oxidation Of Cyclic Sulfamides To Imines

Cyclic N-sulfonyl and sulfamate-derived imines are key structural motifs in natural compounds and medicines.Therefore,sulfamate and sulfonamide functional groups are often incorporated into the target molecules for improving pharmacological potency.Moreover,cyclic N-sulfonyl imines have been widely used as important intermediates in various asymmetric transformations,particularly in arylation reaction,showing high reactivity and enantioselectivity.Visible-light photoredox catalysis has evolved into a widely used method in organic synthesis in the past decade.The photocatalyst can efficiently promote some chemical reactions under visible light irradiation and mild conditions.Photocatalysis not only reduces the cost,but also reduces the pollution,which fully meets the requirements of green chemistry.This dissertation described a research on visible-light photocatalytic aerobic oxidation of cyclic sulfamides for the efficient synthesis of cyclic N-sulfonyl imines.The following research results were obtained.?1?11 five-membered cyclic sulfonamide substrates were synthesized starting from saccharin through nucleophilic addition and reduction.10 six-membered cyclic sulfonamide substrates were synthesized starting from salicylaldehyde through nucleophilic addition,IBX oxidation,dehydration condensation and reduction.Among them,8 substrates are new compounds.These above compounds have been well characterized.?2?With 3-phenyl-1,2-benzothiazoline 1,1-dioxide as the model substrate,the optimal reaction condition was established:Ir?ppy?₂?dtbpy?PF₆ as photocatalyst,KF·2H₂O as base,MeCN as solvent,blue LED as light source and stirring at room temperature for 12 hours.Under the optimal conditions,the model compound can give the imine product in 98%separation yield.?3?With the optimal reaction condition,almost all the aryl substituted substrates per-formed oxidative dehydrogenation very well.3-substituted 1,2-benzothiazoline-1,1-dioxides and 4-substituted 1,2,3-benzoxazolidine-2,2-dioxides were smoothly oxidized into the corresponding imines in 69%⁹8%yields.Finally,we proposed a plausible mechanism of photocatalytic oxidation based on the results control experiments.?4?Exploring the oxidation performance of non-metallic photocatalysts Eosin Y and g-C₃N₄ by catalyzing five-membered cyclic sulfonamide to imines.By optimizing the reaction conditions,the optimal reaction condition of Eosin Y was established:Cs₂CO₃ as base,THF as solvent,48W 410 nm LED as light source and stirring at room temperature for12 hours,and the oxidation yield was 96%.The optimal reaction condition of g-C₃N₄ was established:K₃PO₄ as base,pyridine as solvent,12W blue LED as light source and stirring at room temperature for 12 hours,and the oxidation yield was 67%.