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Base‐Controlled Palladium‐Catalyzed Intramolecular 'One Substrate − Five Reactions' of 5‐Benzyl‐1‐(2‐halobenzyl)‐2‐phenyl‐1H‐pyrazol‐3(2H)‐ones

Achieving site-selectivity and chemoselectivity is enormously challenging for substrates with multi-reactive sites in organic reactions. Here, we chose one kind of model substrates, 5-benzyl-1-(2-halobenzyl)-2-phenyl-1H-pyrazol-3(2H)-ones with six reactive sites as the examples to probe their intramolecular four kinds of five reactions including C(sp3)-H arylation, C(sp2)-H arylation, reductive Heck reaction, and domino Heck reaction/alkylation of aryl C(sp2)−H bonds through variation of the reaction conditions. When we screened the reaction conditions, we inspiringly found that the different bases controlled the palladium-catalyzed intramolecular site-selectivity and chemoselectivity of the substrates: (i) Cesium carbonate (Cs2CO3) promoted the benzyl C(sp3)−H arylation of the substrates providing dihydropyrazolo[1,5-b]isoquinolin-2(1H)-ones at 100 oC, and isomerization of the dihydropyrazolo[1,5-b]isoquinolin-2(1H)-ones gave isoquinoline derivatives at a higher temperature (140 oC); (ii) Sodium acetate (NaOAc) mediated the aryl C(sp2)−H arylation of the substrates affording seven-membered biphenyl N-heterocycles; (iii) Sodium dichloroacetate (Cl2HCCO2Na) facilitated occurrence of the reductive Heck reaction of the substrates affording 1H-pyrazolo[5,1-a]isoindol-2(8H)-ones; (iv) Sodium trifluoroacetate (F3CCO2Na) assisted performance of the domino Heck reaction/aryl C(sp2)−H alkylation of the substrates leading to the spiro heterocycles. The ‘one substrate − multiple reactions − multiple products’ strategy greatly reduces cost, increases diversity of products, provides more opportunity for screening of pharmaceutical molecules, and enriches modern organic synthetic chemistry.

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