2,2-Dimethyl-3-pentanone → 5-Methyl-2,3-dihydro-benzo[1,4]dioxine-6-carboxylic acid n'-(1-ethyl-2,2-dimethyl-propyl)-hydrazide

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Reaction Steps

0.86 g (4.1 mmol) of -methyl-2,3-dihydro-benzo[1,4]dioxine-6-carboxylic acid hydrazide and 1.14 g (10 mmol) of 2,2 dimethyl pentan-3-one, 30 mL of ethyl alcohol and 20 drops of glacial acetic acid were refluxed for 6 hours. TLC indicated ca. a 60% conversion to 5-methyl-2,3-dihydro-benzo[1,4]dioxine-6-carboxylic acid (1-ethyl-2,2-dimethyl-propylidene)-hydrazide (Rf=0.40, 1:1 ethyl acetate:hexane). The reaction was cooled, 3 mL of glacial acetic acid followed by 0.63 g (10 mmol) of sodium cyanoborohydride were added, and the reaction was stirred at room temperature for 3 hours. Most of the alcohol was removed on a rotary evaporator. 30 mL of water was added, followed by the addition of 10% NaOH/H2O until the reaction mixture was basic. The mixture was extracted extensively with ethyl acetate. The ethyl acetate extract was dried and evaporated to give 1.2 g of crude material. The product was purified by column chromatography on silica gel, eluting with 20-30% ethyl acetate/hexane. About 0.46 g of pure 5-methyl-2,3-dihydro-benzo[1,4]dioxine-6-carboxylic acid N′-(1-ethyl-2,2-dimethyl-propyl)-hydrazide was obtained. TLC: Rf=0.46 (1:1 ethyl acetate:hexane). 1H NMR (CDCl3, 500 MHz) δ (ppm): 7.1 (br, 1H[NH]), 6.85 (d, 1H), 6.71 (d, 1H), 4.8 (br, 1H), 4.29 (m, 2H), 4.25 (m, 2H), 2.4 (m, 1H), 2.29 (s, 3H), 1.7 (m, 1H), 1.3 (m, 1H), 1.15 (t, 3H), 0.98 (s, 9H).

Provenance & Evidence