Sulfuric Acid → 6'-(3,4-dihydro-2H-quinoxalin-1-yl)-2,3,5,6-tetrahydro-[1,3']bipyridinyl-4-one

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Reaction Steps

In a 150-ml flask, 5.51 g of tert-butyl ester of 4-[5-(1,4-dioxa-8-aza-spiro[4.5]dec-8-yl)-pyridin-2-yl]-3,4-dihydro-2H-quinoxaline-1-carboxylic acid (intermediate 7.1) is put in 21 ml of tetrahydrofuran, 21 ml of water and 20 ml of acetone. It is cooled on an ice bath and 8.24 ml of 95% sulfuric acid is added gently. It is stirred at room temperature for 18 h. The solution is then poured into water. 5N sodium hydroxide is added to basic pH and it is extracted twice with ethyl acetate. The combined organic phases are washed with water, dried over sodium sulfate, filtered and evaporated to dryness. The raw product obtained is chromatographed on silica gel, eluting with a gradient of ternary solvents, on the one hand heptane and on the other hand heptane/ethyl acetate/methanol 4/5/1 varying from 10% to 100%. 2.39 g of 6′-(3,4-dihydro-2H-quinoxalin-1-yl)-2,3,5,6-tetrahydro-[1,3′]bipyridinyl-4-one is obtained.

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