铑催化苯甲酰亚胺导向C—H活化合成茚[1,2-c]异喹啉-11-酮

Synthesis of Indene[1,2-c]isoquinoline-11-one by Rhodium-catalyzed Benzimide-directed C—H Activation

茚并[1,2-c]异喹啉是一类非常重要的有机杂环骨架,在药物化学、有机光电材料方面有着广泛的应用.本工作以苯甲酰亚胺乙酯及α-重氮-1,3-二酮为底物,通过金属铑催化,构建了茚[1,2-c]异喹啉酮骨架.进一步通过还原反应,高效合成具有生物活性的茚并[1,2-c]异喹啉产物.该反应具有良好的底物普适性和官能团兼容性.机理试验表明该反应可能经历了五元环铑中间体,且碳氢键活化为反应的决速步.

Indene[1,2-c]isoquinoline is a novel non-camptothecin-like Topo1 inhibitor,and possesses good antitumour effect on lung cancer,lymphoma,etc.Thus,the development of new methodologies to construct indene[1,2-c]isoquinoline and its derivatives has been a hot topic in organic chemistry.In recent years,benzimidate has been widely used as a building block in the construction of nitrogen-containing heterocycles via transition metal-catalyzed C(sp2)—H bond activation and subsequent cyclization reaction with different reagents,such as alkyne,alkene,carbenes.Meanwhile,α-diazo carbonyl compounds have been widely used as C2 synthons in organic synthesis.In particular,with cyclicα-diazo-1,3-diketones,fused polycyclic compounds could also be prepared via Rh(III)-catalyzed[4+2]oxidative annulations.Herein,we report the construction of indene[1,2-c]isoquinoline-11-one using benzimidate andα-diazo carbonyl compounds as the starting material.The reaction proceeds via a rhodium-catalyzed C—H activation/carbenoid insertion/dehydration process.The protocol showed high atom economy,excellent functional group tolerance,and heterocycle compatibility,giving the indene[1,2-c]isoquinoline-11-one in moderate-to-good yields.Wolff-Kishner reduction of the product with N2H4•H2O affords the indene[1,2-c]isoquinoline.To demonstrate the synthetic utility of this protocol,gram-scale synthesis and late-stage modification of drug molecule were showcased.The KIE value of 3.4∶1 indicated that the C—H cleavage step is probably involved in the rate-determined step.A typical general procedure for the synthesis of indene[1,2-c]isoquinoline-11-one 3a is described as the following:To a solu-tion of ethyl benzimidate(0.1 mmol),[Cp*RhCl2]2(1.5 mg,2.5 mol%),and AgOAc(3.2 mg,20 mol%)in hexafluoroisopro-panol(2 mL)was added diazooxindole(0.11 mmol)under N2.The mixture was stirred at 100℃for 12 h.Then the reaction mixture was cooled to room temperature.The mixture was filtered through Celite,and the filtrate was evaporated to give the crude product which was then purified by flash column chromatography on silica gel with a gradient eluent of petroleum ether/ethyl acetate(V/V,10/1)to give the product 3a.