Dimethoxyindole

Similar to the Fisher indole synthesis, reductive cyclization of nitro aromatics offers a powerful means of forming indoles. Reductive cyclization of ortho, 2 -dinitrostyrenes has occurred in many ways, by TiCl3, NaBH4-Pd/C, H2-Pcl/C, and other reductive methods.89 Corey and coworkers have used the Borchardt modification (Fe-AcOFI, sihca gel, toluene at reflux for the reductive cyclization of o-ji-dinitrostyrenes) to prepare 6,7-dimethoxyindole (Eq. 10.65) in a total synthesis of aspidophytine (see Schemes 3.3 and 3.4 in Section 3.2.l).89d... 

Lion and colleagues prepared 5,6,7-trimethoxyindole for a molecular mimic of combretastatin [30], and indole 21 became the indole unit in rapalexin B in a synthesis of this cruciferous phytoalexin by Pedras and colleagues [31], Indole 22 was needed for a biosynthetic study of the paraherquamide natural products [32], and Corey s team employed 6,7-dimethoxyindole (16) (71%) in their synthesis of aspidophytine [33]. 

The trifluoromethyl derivative 146 has been obtained as a minor product from the reaction of (l-methyhndol-3-yl)methanol with trifluoroacetic acid anhydride (TFAA), the major product (22% yield) being 6-trifluoromethylindolo[3,2-()]-carbazole [98LTC(B)841]. Several substituted indolo[2,3-()]carbazoles have also been encountered during studies on the reaction of 4,6-dimethoxyindole with... 

In order to probe the reactivity of the C-7 position, without the possible complication of the formation of regioisomers, 4,6-dimethoxy-2,3-diphenylindole 3a was prepared by the Bischler reaction from 3,5-di-methoxyaniline and benzoin.3 Vilsmeier formylation occurred smoothly to give the 7-carbaldehyde 4a in 82% yield. In a related manner, the other 2,3-disubstituted-4,6-dimethoxyindoles 3b-d3 were converted in yields of 62-70% to the corresponding 7-carbaldehydes 4b-d4,5 (Scheme 2). More recently, the tetrahydrocarbazole 3e6,7 was also formylated at the equivalent 8-position in 82% yield.7... 

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