Reactions of 7H-naphth[3,2,1-cd]azulen-7-ones

Abstract

6-Chloro-7H-naphth[3,2,1-cd]azulen-7-ones 9a and 10a easily react with some nucleophiles (sodium methoxide, potassium hydrosulfide, and amines) to give the corresponding 6-substituted products. Halogenation of 7H-naphth[3,2,1-cd]azulen-7-ones with N-halosuccinimides occurs at the C-5 position. Grignard reagents add to 7H-naphth[3,2,1-cd]azulen-7-ones at the seven-membered ring and a subsequent dehydrogenation gives 2-, 3- and 4-substituted products; reactive tendency of the positions of 7H-naphth[3,2,1-cd]azulen-7-one toward the reagents was 6 ≫ 3 > 4 > 2, whereas the steric hindrance was (6 >) 4 > 3 > 2. Condensation of 7H-naphth[3,2,1-cd]azulen-7-ones with active methylene compounds in boiling acetic anhydride occurs at the carbonyl group and gives the corresponding 7-methylene-7H-naphth[3,2,1-cd]azulene derivatives. 6-Hydroxy-7H-naphth[3,2,1-cd]azulen-7-one 7 is obtained by the hydrolysis of 6-methoxy-7H-naphth[3,2,1-cd]azulen-7-one 9b with hydrobromic acid, in almost quantitative yield. Compound 7 exists in a tautomeric mixture with 7-hydroxy-6H-naphth[3,2,1-cd]azulen-6-one 8. Methylation of 7 with diazomethane gives 9b and 7-methoxy-6H-naphth[3,2,1-cd]azulen-6-one 18a in 75% and 25% yield, respectively. Chlorination of 7 with thionyl dichloride also gives a pair of isomers, 5,6-dichloro-7H-naphth[3,2,1-cd]azulen-7-one 11b and 5,7-dichloro-6H-naphth[3,2,1-cd]azulen-6-one 18b. A tautomerism between 6-(substituted methyl)-7H-naphth[3,2,1-cd]azulen-7-ones and 7-hydroxy-6H-naphth[3,2,1-cd]azulen-6-ylidenemethylene derivative is also studied.