102237-53-6Relevant articles and documents
Synthetic Studies of Indoles and Related Compounds, Part 221. The Vilsmeier-Haack Reaction of N-Benzyl-1,2,3,4-tetrahydrocarbazoles and its Synthetic Application to Olivacine and Ellipticine2
Yokoyama, Yuusaku,Okuyama, Naomi,Iwadate, Shinji,Momoi, Tokuko,Murakami, Yasuoki
, p. 1319 - 1329 (2007/10/02)
Vilsmeier-Haack reaction of 9-benzyl-1,2,3,4-tetrahydrocarbazole (18a) at 120 deg C gave 9-benzyl-1-methylcarbazole-3-carbaldehyde (19a) and 9-benzyl-1-(N,N-(dimethylamino)methyl)carbazole-3-carbaldehyde (22a) in moderate yields, whereas, the same reaction at 0 deg C gave 9-benzyl-1,2,3,4-tetrahydrocarbazole-1-carbaldehyde (20a) in very good yield.The aldehyde (20a) was converted into 9-benzyl-1-methylcarbazole (21a) by another Vilsmeier-Haack reaction.This carbazole (21a) unexpectedly underwent non-regioselective formylation under similar reaction conditions to give a mixture of compound (19a) and 9-benzyl-8-methylcarbazole-3-carbaldehyde (23a).On the basis of the above results, a mechanism of the formation of the aromatic aldehyde (19a) was proposed, which involves 1,5-sigmatropic rearrangement of an N-methylidene dimethylammonium cation from the 4a-position to the 3-position as a key step.Vilsmeier-Haack reaction of 9-benzyl-1,2,3,4-tetrahydro-4-methylcarbazole (18b) at 100 deg C also gave 9-benzyl-1,4-dimethylcarbazole-3-carbaldehyde (19b) in moderate yield.The total syntheses of two antitumor alkaloids, olivacine (10) and ellipticine (11), were achieved by utilizing compounds (19a) and (19b) as key intermediates.
