Synthesis of β-Sulfonyl Enamines via Iodine-Catalyzed Reaction between Vinyl Azides and Sodium Arylsulfinates

Abstract

The present protocol provides the facile and highly efficient synthesis of various Z-structure N-unprotected β-sulfonyl enamine compounds in a manner by using inexpensive molecular iodine as catalyst, vinyl azides as free radical acceptor, and sodium arylsulfinates as free radical sources. In this reaction, ethanol was used as solvent and bistrifluoromethanesulfonimide (Tf2NH) was used as additive. The reaction was carried out at 40 ℃ for 4～6 h to obtain β-sulfonyl enamine compounds with good yields. The method does not need to use metal catalyst, and has the advantages of simple conditions, short reaction time and wide substrate application range. Keywords iodine catalysis; vinyl azide; free radical addition; sulfonyl enamine 乙烯基叠氮化合物 [1][2][3] 是同时具有双键和叠氮基团 的分子, 该类分子由 Forster 和 Newman [4] 首次提出并报 道, 到现在已经有近一百年的历史 [5][6] . 其拥有单独的烯 烃或叠氮基结构所没有的独特性质, 它可以作为亲电试 剂 [7][8] 、亲核试剂 [9][10][11][12][13] 或自由基受体 [14][15][16][17][18][19] 等, 同时能够通 过多种反应途径生成各类高反应活性的中间体 [20] , 因 此这类化合物在有机合成方面具有非常重要的作用. 在 过去的十几年中, 乙烯基叠氮化合物得到了很好的发 展, 这也是由于过渡金属催化的强大推动力以及实际制 备方法的最新发展所致. 乙烯基叠氮的大量化学转化反 应为各种结构不同的分子骨架提供了可靠的合成方法, 这些骨架通常包括杂/碳环、酰胺、酮和 2H-氮丙啶等. 苯亚磺酸钠盐是一种廉价易得、反应活性高、绿色 环保且高效清洁的磺酰化试剂, 可替代磺酰氯 [21] 、硫醚 和硫脲等含硫化合物进行磺酰化反应, 近几年在有机合 成领域也受到了越来越多的关注. 在一定条件下, 苯亚 磺酸钠可以形成磺酰基自由基 [22][23][24] , 乙烯基叠氮作为自 由基受体与磺酰基自由基进行反应 [25] . 另一方面, 单质 碘作为一类简便易得、性质稳定的化学试剂, 其温和的 氧化性可以将 C-H 键高效地转化为 C-C, C-N 以及 C-O 键 [26] .

Copper-Catalyzed Radical Relay 1,3-Carbocarbonylation across Two Distinct C═C Bonds

“…On the basis of the control experiments and the previous related reports, ,,− we tentatively propose a reaction mechanism in Figure . First, as a radical precursor, α-carbonyl alkyl bromide 1 undergoes SET under Cu I to produce an alkyl carbon radical intermediate I , , which simultaneously releases [Cu II ]-Br.…”

“…Subsequently, the intramolecular cyclization of intermediate I produced a new alkyl radical intermediate II , which was confirmed with radical inhibitor adduction ( 5a – 7a and 9a ) by HRMS assay. Next, the rapid denitrogenization after radical relay reaction between intermediate II with the CC bonds of vinyl azide 2 produces imine radical intermediate III , and the adduct ( 8a ) of the key intermediate with BHT is also detected by HRMS. Lastly, the protonation of III occurs to yield intermediate IV , which is converted into the final product 3 through rapid hydrolysis in the presence of H 2 O …”

Nickel-Catalyzed Reaction between Vinyl Azides and an Alkyl Sulfonyl Radical Generated from DMSO: Rapid Access to β-Keto Sulfones

“…Vinyl azides as a crucial class of synthons have received extensive attention from organic chemists in chemical synthesis. − In this context, the addition reactions of vinyl azides with sulfonyl radicals are prominent, providing a reliable pathway to construct β-keto sulfones, enamines, phenanthridines, etc. (Scheme C). − Among them, β-keto sulfones are commonly employed as a critical synthetic building block in organic syntheses. − Notably, a series of reactions using sulfonyl hydrazines as the source of sulfonyl radicals to react with vinyl azides for the preparation of β-keto sulfones have been reported. ,,, In 2023, our group has developed a copper-catalyzed multicomponent cascade reaction for the synthesis of β-keto sulfones from vinyl azides, oxime esters, and Na 2 S 2 O 5 .…”

Visible-Light-Driven Unsymmetric gem-Difunctionalization of Vinyl Azides with Thiosulfonates or Selenosulfonates

“…Vinyl azides make up a structurally unique class, and directly selective functionalization of vinyl azides is attractive for the assembly of various complex molecular entities. In the past decade, the vinyl azide chemistry renaissance in the field of photochemistry has been witnessed, as proven by the enormous number of novel transformations reported in the literature . Ketones, imines, and unsubstituted amines , can all be obtained from vinyl azide compounds via the radical pathway.…”