Improved Synthetic Method for 5-[(Phenylthio)methyl]oxazoline Derivatives: Electrophilic Cyclization of Allylic Amide Using a Brønsted Acid and Tetrabutylammonium Chloride under Mild Conditions

Abstract

The synthesis of oxazolines using electrophilic cyclization of allylic amide is a simple and powerful method. However, cyclization involving arylsulfenylation requires harsh reaction conditions. We found that the reaction proceeds under mild heating conditions with the combination of a Brønsted acid and tetrabutylammonium chloride. This method enabled the synthesis of 5-[(arylsulfenyl)methyl]oxazoline derivatives under mild conditions and demonstrated high tolerance for various functional groups.

N-Sulfenylsuccinimide/phthalimide: an alternative sulfenylating reagent in organic transformations

“…The attack of the sulfonamide nitrogen atom on this intermediate led to intramolecular cyclization. In 2020, electrophilic cyclization of allylic amides 134 using N -(phenylthio)succinimide 1 in the presence of camphorsulfonic acid (CSA) as a Brønsted acid and tetrabutylammonium chloride (TBAC) led to 5-[(phenylthio)methyl]oxazoline scaffolds 135 ( Scheme 57 ) [ 89 ]. Combination of CSA/TBAC formed an efficient activator system for this sulfenylation/intramolecular cyclization.…”

Structures and Synthetic Strategies of Chiral Oxazolinyl Ferrocene Derivatives

“…如前 文所述不难看出, 大部分噁唑啉成环过程需要使用当量 的酸或酰氯进行反应, 部分结构复杂的底物关环过程甚 至需要活性较高反应试剂(如 DAST、Burgess 试剂等) 参与, 对于反应操作及相应后处理增加了不小难度. 目 前, 以催化方法得到噁唑啉环方式不断出现 [133][134][135][136][137][138] , 但 能够高效应用于手性噁唑啉二茂铁化合物催化合成方 法并不多见. 开发新型催化方式合成噁唑啉二茂铁衍生 物的方法, 将为进一步降低成本、提高合成效率提供关 键技术基础.…”