4- Iodoindole-3-carboxaldehyde

Somei improved this methodology by quenching the appropriate thallated intermediate with 12/CuI/DMF to give 4-iodoindole-3-carboxaldehyde in 94% yield [39], and he extended this method to achieve efficient syntheses of C-7 haloindoles [40, 41], For example, 7-iodoindole (33) was prepared in good overall yield from A-acetylindoline as illustrated. Thallation at C-5 is a minor (5%) pathway. 

Iodoindole-3-carboxaldehyde, when irradiated in benzene or furan in the presence of a trace amount of pyridine, gives the 4-phenyl or 4-(2-furyl) derivatives in 60% and 64% yields, respectively529. 

Somei improved this methodology by quenching the appropriate thallated intermediate with I2/CUI/DMF to give 4-iodoindole-3-carboxaldehyde in 94% yield [39], and he... 

Comins used their aminoalkoxide methodology [323] to direct C2-lithiation with an indole-3-carboxaldehyde substrate [324]. Kitagaki and Mukai later used the Comins strategy to prepare a 2-iodoindole-3-carboxaldehyde, a precursor to a 2,3-bis(alkynyl)indole [325]. This strategy was also applied by Comins to direct lateral lithiation onto an A-methyl group from an aminoalkoxide generated at C2 [77]. 

The isoquinoline 61 was obtained by the reaction of t-butylimine 60 of 0-iodobenzaldehyde with internal alkyne [20], The reaction was extended to synthesis of the y-carboline 65 from the r-butylimine of A -methyl-2-iodoindole-3-carboxaldehyde 62 [21], The reaction is explained by 6-endo cyclization of the alkenylpalladium intermediate 63, followed by elimination of /i-t-butyl group as isobutylene as shown by 64. This mechanism explains the importance of t-butylimine in this cyclization. 

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