Benzyl 3-oxopiperazine-1-carboxylate → 5-Ethoxy-3,6-dihydro-2H-pyrazine-1-carboxylic acid benzyl ester

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Reaction Steps

To a solution of 3-oxo-piperazine-1-carboxylic acid benzyl ester (2.0 g, 8.54 mmol, Maybridge) in dichloromethane (18 mL) at room temperature was added triethyloxonium tetrafluoroborate (4.1 g, 21.3 mmol). This mixture was allowed to stir for about 3 days then quenched by the addition of ice chips followed by saturated aqueous sodium bicarbonate until a neutral pH was obtained. The organic layer was separated and the aqueous layer was extracted with chloroform (3×). The combined organic extracts were washed with brine (1×), dried over sodium sulfate, and concentrated to give 2.11 g (95%) of the title compound of Example 259, Step A as a slightly yellow oil that was sufficiently pure to carry on to the next step. 1H NMR (CDCl3, 300 MHz) δ 7.43-6.97 (c, 5H), 5.17 (s, 2H), 4.10 (q, 2H), 3.98 (s, 2H), 3.60-3.40 (c, 4H), 1.27 (t, 3H); MS (APCI) 263 (MH+).

Provenance & Evidence