An Unusual and Chemoselective Reduction of Ester Grouping in Nsubstituted-3-acetylindoles by Sodium Borohydride
作者:Muvvala Venkatanarayana、Pramod K. Dubey
DOI:10.2174/157017812800167402
日期:2012.3.1
Treatment of 3-acetylindoles 1(a-e) with ethyl chloroacetate in the presence of K2CO3 and tetrabutylammoniumbromide (TBAB) as phase transfer catalyst in DMF, resulted in the formation of the corresponding N-substituted derivatives, ethyl 2-(3-acetyl-1H-indol-1-yl)acetate 2(a-e) which on reaction with NaBH4 yielded, unexpectedly, ethanol derivatives, 1-(1-(2-hydroxyethyl)-1H-indol-3-yl)ethanone 3(a-e) by the unusual and chemoselective reduction of ester grouping in preference to the acetyl group. Alternative synthesis of the latter was achieved by the treatment of 1(a-e) with 2-chloroethanol under phase transfer catalytic conditions (PTC). 1(a-e), on treatment with benzenesulphonyl chloride, under PTC conditions, yielded the corresponding N-benzenesulphonyl-3- acetylindoles 7(a-e), which on reduction with NaBH4 in methanol afforded the corresponding hydroxy derivatives Nbenzenesulphonyl-( α-hydroxyethyl)indoles 8(a-e). These reactions throw light on the ease of reduction of the 3-acetyl group on indoles with NaBH4.
用K2CO3和四丁基溴化铵(TBAB)作为相转移催化剂,在DMF中处理3-乙酰吲哚1(a-e)与氯乙酸乙酯,生成相应的N取代衍生物,即乙基2-(3-乙酰-1H-吲哚-1-基)乙酸酯2(a-e)。这些衍生物与NaBH4反应时,意外地产生了乙醇衍生物1-(1-(2-羟乙基)-1H-吲哚-3-基)乙酮3(a-e),这是因为酯基的还原优先于乙酰基。通过在相转移催化条件(PDC)下用2-氯乙醇处理1(a-e),也能合成后者。1(a-e)在相转移催化条件下与苯磺酰氯反应,生成相应的N-苯磺酰基-3-乙酰吲哚7(a-e),这些化合物在甲醇中与NaBH4还原后得到相应的羟基衍生物N-苯磺酰基-(α-羟乙基)吲哚8(a-e)。这些反应说明了使用NaBH4还原吲哚中的3-乙酰基的简单性。