Dibrominative Spirocyclization of 2-Butynolyl Anilides: Synthesis of <i>gem</i>-Dibromospirocyclic Benzo[<i>d</i>][1,3]oxazines and Their Application in the Synthesis of 4<i>H</i>-Furo[3,2-<i>b</i>]indoles
作者:Nattawadee Chaisan、Sureeporn Ruengsangtongkul、Jumreang Tummatorn、Somsak Ruchirawat、Kittipong Chainok、Charnsak Thongsornkleeb
DOI:10.1021/acs.joc.1c00086
日期:2021.3.19
The combination of catalytic aqueous hydrochloric acid (HCl) and N-bromosuccinimide (NBS) generated electrophilic bromine monochloride (BrCl), which readily induced spiroannulation of 2-alkynolyl anilides (n = 1–3) to form gem-dibromospirocyclic benzo[d][1,3]oxazines in up to 92% yield. The reaction occurred under mild and metal-free conditions using EtOAc as a green solvent. The resulted spirocyclic
催化盐酸水溶液(HCl)和N-溴代琥珀酰亚胺(NBS)的结合产生亲电的一氯化溴(BrCl),该溶液很容易诱导2-炔基苯甲酰胺(n = 1-3)的螺环化反应,形成宝石-二溴螺环苯并[ d ] [1,3]恶嗪的产率高达92%。反应在温和且无金属的条件下进行,使用EtOAc作为绿色溶剂。所得的螺环产物包含苯并[ d ] [1,3]恶嗪,其既可以用作药效基团,也可以用作合成前体。此外,当前协议允许毫不费力地引入sp 3 - gem-二溴碳与空间要求很高的螺环中心相邻。这些螺旋杂环(n = 1)被证明具有通用性,并且操作方便。这些螺环的碱促进的脱溴化芳构化以极好的收率掩盖了稀有的和合成上有用的2-芳基-3-溴呋喃。这些3-溴呋喃是分子内Ullmann C–N键偶合以构建难以制备的4 H -furo [3,2- b ]吲哚的合适底物。另外,当前的方案是灵活的并且可适应于制备宝石-二氯化物变体。