Functional group removal, halogen tributyltin hydride

Radical substitution reactions can also be used to remove functional groups from molecules. A useful reagent for this (and, as you will see, for other radical reactions too) is tributyltin hydride, Bu3SnH. The Sn-H bond is weak and B SnH will react with alkyl halides to replace the halogen atom with H, producing BL SnHal as a by-product. 

This ring may be built by the formation of a new C—C bond between alkyne and halogen functions, a reaction which is assisted by palladium dichloride-triphenylphosphtne (reviews of palladium catalysis [IMI, 3069, 3505] in the presence of piperidine (as base) and formic acid (to remove hydride ion). The reaction is regio- and stereo-selective. Replacement of the piperidine and formic acid by R-substituted tributyltin enables the R group to be transferred to the indole stereospectfically [3448]. 

---