Cadogan反应还原2-硝基苯基芴得咔唑

Synthesis of Carbazoles by Cadogan Reaction of 2-Nitrophenyl-fluorene

由Cadogan反应,2-硝基联苯在有机磷试剂存在下,硝基被还原成环得到咔唑类化合物得到启发,设计两步反应,第一步邻溴硝基苯与9,9-二甲基2-芴硼酸为原料经Suzuki偶联反应,甲苯中回流,得到芴与2-硝基苯的C-C偶联化合物;第二步Cadogan环化反应,三苯基膦还原2-(2-硝基苯)-9,9-二甲基芴得咔唑。这一设计重点在于合成咔唑的同时成功地引入了芴核,新合成的化合物通过共用苯环而包含了咔唑和芴。尽管用Cadogan反应还原2-(2-硝基苯)-9,9-二甲基芴时有两种关环可能,但该方法仍然简单有效,易于控制。副产品包括三苯基氧化膦和咔唑异构体12,12-二甲基-11,12-二氢茚[2,1-a]咔唑非常容易通过柱层析除去。

Inspired by the Cadogan reaction, by which the carbazole compounds are obtained by redaction of 2-nitryl biphenyl in the presence of organophosphorus, a two-step reaction is design. Firstly, the C-C coupling compound of 2-nitropheny[-fluorene is obtained via Suzuki cross-coupllng reaction between the 9,9-dimethyl 2-fluorene boronic acid and the o-bromonitrobenzene in toluene. Secondly, the carbazole is obtained by reduction of2-（2-nitrophenyl）-9,9-dimethyl fluorene with using triphenylphosphine by the Cadogan reaction. A novel soluble carbazole compound is synthesized in which the structure of benzene is shared so as to contain the fluorene and carbazole. The new reaction is very simple and effective, and easy to control, although there are 2 possibilities of ring closure when reaction of 2-（2-nitrophenyl）-9,9-dimethyl fluorene. The byproducts including triph- enylphosphine oxide and the isomer 12,12-dimethyl-11,12-dihydroindene[2,1-a]carbazole are easy to remove by column chromatography.