Diisopropyl Ether → Pyrano(2,3-g)indole-2-carboxylic acid, 1,7,8,9-tetrahydro-

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Reaction Steps

7,8-Dihydro-9H-pyrano[2,3-g]indole-2-carboxylic acid, 6,7-dihydro-5H-pyrano[3,2-f]indole-2-carboxylic acid and 5,6-dihydro-7H-pyrano[2,3-e]indole-2-carboxylic acid were prepared according to the method described in Example 3, using a mixture (10:5:2) of methyl 7,8-dihydro-9H-pyrano[2,3-g]indole -2-carboxylate, methyl 6,7-dihydro-5H-pyrano[3,2-f]indole -2-carboxylate and methyl 5,6-dihydro-7H-pyrano[2,3-e]indole -2-carboxylate (4.33 g, 18.7 mmol) to produce, after trituration with isopropyl ether, a mixture [(2,3-g):(3,2-f):(2,3-e)—7:1:2] of products (2.30 g, 57%) as a white solid. The filtrate was evaporated and purified by flash column chromatography [SiO2; ethyl acetate-heptane (2:1)+0.5% acetic acid] to afford an oil which solidified upon treatment with isopropyl ether-heptane to afford a mixture [(2,3-g):(3,2-f):(2,3-e)—44:22:34] of products (818 mg, 20%) as a white solid. The products were combined and used without further purification.

Provenance & Evidence