可见光促进荧光素催化的氧化偶联反应合成苯并咪唑[2,1-a]异喹啉-6(5H)-酮衍生物

Visible light promoting fluorescein catalyzed oxidative coupling for synthesis of benzimidazo[2,1-a]isoquinolin-6(5H)-ones

室温下,以N-苯并咪唑丙烯酰胺类化合物为自由基受体,1,3-二氧戊烷为自由基来源,荧光素为催化剂,在可见光驱动下通过自由基加成/环化反应制备了苯并咪唑[2,1-a]异喹啉-6(5H)-酮衍生物。以2-甲基-1-[2-苯基-苯并(d)咪唑]-2-烯-1-酮(Ⅰa)和1,3-二氧戊烷为原料,考察了催化剂、氧化剂、溶剂对5-[(1,3-二氧戊基-2-基)甲基]-5-甲基苯并[4,5]咪唑[2,1-a]异喹啉-6(5H)-酮(Ⅲa)产率的影响。得到合成Ⅲa的最佳反应条件为:Ⅰa 0.25mmol、荧光素0.0125 mmol、1,3-二氧戊烷2 mL、叔丁基过氧化氢(氧化剂)0.75 mmol,室温蓝光(LED,10 W,波长450~455 nm)下搅拌反应20 h。在上述反应条件下,以48%~78%产率合成了11种具有不同取代基的苯并咪唑[2,1-a]异喹啉-6(5H)-酮衍生物,采用^(1)HNMR、^(13)CNMR对终产物进行了结构鉴定。

Benzimidazo[2,1-a]isoquinolin-6(5H)-one derivatives were prepared by radical addition/cyclization reaction using N-benzimidazo[2,1-a]acrylamide compounds as free radical receptor,1,3-dioxolane as free radical source,and fluorescein as catalyst at room temperature under visible-light irradiation.The effects of catalysts,oxidants and solvents on the yield of 5-[(1,3-dioxopentyl-2-yl)methyl]-5-methylbenzo[4,5]imidazole[2,1-a]isoquinoline-6(5H)-one(Ⅲa)were investigated with 2-methyl-1-[2-phenyl-benzo(d)imidazole]-2-ene-1-one(Ⅰa)and 1,3-dioxolane as raw materials.The optimum reaction conditions for the synthesis of Ⅲa were as follows:Ⅰa 0.25 mmol,fluorescein 0.0125 mmol,1,3-dioxolane 2 mL,tertbutylhydrogen peroxide as oxidant 0.75 mmol,under blue light(LED,10 W,wavelength 450~455 nm)irradiation and reaction time of 20 h.Under the above reaction conditions,eleven benzimidazo[2,1-a]isoquinolin-6(5H)-one derivatives with different substituents were obtained with yields ranging from 48%~78%.The structures of products were confirmed by ^(1)HNMR and ^(13)CNMR.