DIAZOTIZATION OF METHYL 3-AMINO-7-ISOPROPYL-2-METHOXYAZULENE-1-CARBOXYLATE AND ITS 5-ISOPROPYL ISOMER - A CONVENIENT SYNTHESIS OF 1,2-AZULENEQUINONE DERIVATIVES

摘要

Methyl 3-amino-2-methoxy-7-isopropylazulene-1-carboxylate (8a) and its 5-isopropyl isomer (8b) were synthesized by reduction of the 3-nitro derivatives (7a,b) with zinc/acetic acid in excellent yields. 7a and 7b were prepared by nitration and methylation of methyl 7-isopropyl-2-hydroxyazulene-1-carboxylate (5a) and methyl 5-isopropyl-2-hydroxyazulene-1-carboxylate (5b), respectively. Diazotization of 8a with sodium nitrite in trifluoroacetic acid at 0 degrees C gave methyl 5-isopropyl-1,2-azulenequinone-3-carboxylate (9a) in 91% yield. Similar reaction of 8b gave the corresponding methyl 7-isopropyl-1,2-azulenequinone-3-carboxylate (9b) in 93% yield. No evidence for the formation of 1-diazo-1,2-azulenequinones was obtained. [References: 10]