Lithium hydroxide, monohydrate → 7,8-Dihydro-2,3-bis(4-methylphenyl)pyrido[2,3-b]pyrazine-5(6H)-heptanoic acid

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Reaction Conditions

Reaction Steps

Ethyl 7-(2,3-dip-tolyl-7,8-dihydropyrido[2,3-b]pyrazin-5(6H)-yl)heptanoate (step 1) was dissolved in THF (94 ml) and lithium hydroxide monohydrate (7.79 g, 186 mmol) in water (94 ml) was added dropwise. The reaction mixture was warmed to 50° C. and stirred for 7.5 hours. The reaction mixture was concentrated in vacuo to remove the THF and diluted with water (500 ml). The pH of the aqueous layer was adjusted to pH 2 with 1 N HCl (100 ml) and extracted with EtOAc (3×500 ml). The combined organic layers were washed with brine (200 ml), dried over anhydrous sodium sulfate and concentrated in vacuo. The crude solid was suspended in TBME/hexane (1:1, 100 ml) and rotated on the rotary evaporator (no vacuum) at RT until crystals formed. The solid was removed by filtration, washed with heptanes (50 ml) and dried at RT overnight. The solid was re-crystallized from a hot mixture of EtOH (211 ml) and water (159 ml). After seeding and stirring for 1 h at 5° C., the crystals were filtered off and the product dried overnight at 40° C. in a vacuum oven to afford the title compound; See Table 4 for characterising data.

Provenance & Evidence