Switching Regioselectivity of β‐Ketothioamides by Means of Iodine Catalysis: Synthesis of Thiazolylidenes and 1,4‐Dithiines

Abstract

An efficient I2 -catalyzed synthesis of thiazolylidenes and 1,4-dithiines from β-ketothioamides (KTAs) has been developed by only controlling the amount of I2 that triggers different cascade reaction sequences by means of [3+2] or [3+3] cyclocondensation in a one-step process. A possible mechanistic proposal for these transformations is presented.

β-Ketothioamides: efficient reagents in the synthesis of heterocycles

“…Recently, we developed an efficient synthetic protocol to synthesize 1,3-thiazolines and 1,4-dithiines by self-condensation reactions of KTAs controlled by I 2 at room temperature. 13 In the presence of 0.5 equivalents of I 2 the 1,3thiazoline derivatives were obtained, and KTAs bearing either electron-donating or electron-withdrawing substituents on the N-phenyl ring or phenyl ring linked to the carbonyl group provided the corresponding products in good yields. However, when KTAs with alkyl amines were used in the presence of 1 equivalent of I 2 , only the homocoupling product 1,4-dithiines were formed in good yields.…”

NEt3-Promoted Construction of Functionalized 4H-Chromenes via [4+2] Cycloaddition Reaction of ortho-Quinone Methides with β-Ketothioamides

“…Recently β-ketothioamides (KTAs) [13] have received much attention as multifunctional building blocks in organic synthesis and have been extensively used in various carbon-carbon and carbon-heteroatom bond-forming reactions for the construction of heterocycles (Scheme 1, modes A～D [14][15][16][17] ). Although significant progress has been made in this field, the discovery of novel reaction should be an interesting project.…”

Tetrabutylammonium Iodide/t-Butylhydroperoxide Catalytic/Oxidative Synthesis of Thiazolylidene Derivatives

“…图式 1 选择的两种 KTAs 的反应类型 Scheme 1 Selected two reaction types of KTAs 我 们 课 题 组 曾 报 道 了 一 种 在 I 2 和 三 乙 烯 二 胺 (DABCO)存在下, KTAs 发生自身缩合反应合成噻唑啉 化合物的方法(Scheme 2a) [11] . 在我们以 KTAs 为合成子 构建多种杂环化合物的研究工作基础上 [12] , 本文报道 一种以 TBAI 为催化剂、TBHP 为氧化剂, 利用 KTAs 为合成砌块与丙二腈在室温条件下合成 4-氨基噻唑啉 类化合物的新方法(Scheme 2b).…”

“…到目前为止, 以 TBAI/TBHP 体系催化氧化 KTAs 的反应尚未见文献报道. [11] (Scheme 3a); 而丙二腈(2)在此条件下并不 图 2 化合物 3b 的单晶结构 Figure 2 X-ray structure of 3b 发生反应(Scheme 3b); 这说明反应的启动来自于 KTAs 而非丙二腈. 另外, 考虑到在 TBAI/TBHP 催化氧化的 反应模式中, 经常会发生自由基反应 [13] , 所以又进行了 两个自由基捕获实验.…”

“…对目标产物 3a 的结构进行仔细分析后, 我们 猜想该反应可能存在一个极性转换的过程, 即将 KTA 转化变为亲电试剂, 然后被亲核试剂丙二腈进攻. 因此, 在反应体系中加入氧化剂以期实现 KTA 的极性转换[11] . 我们选择了绿色催化氧化体系 TBAI/TBHP.…”