Pyrrolo pyridine, lithiation

The benzenesulfonyl substituent has also been used in conjunction with the lithiation of an azaindole derivative (86FRP2574406 89FRP26274931), and thus 1-benzenesulfonyl-1//-pyrrolo[3,2-c ]pyridine was able to be successfully lithiated and alkylated with p-methoxybenzaldehyde, although reaction with more hindered ketones could not be achieved (Scheme 19)[91JCS(P1)3I73]. 

Lithiation of 2- and 4-t-butoxycarbonylaminopyridines can only take place at C-3 a neat sequence involving, hrst, ring hthiation to allow introduction of a methyl group and, second, side-chain methyl hthiation (8.10), provides one route to azaindoles (20.16), as illustrated below for the synthesis of 5-azaindole (pyrrolo[3,2-c]pyridine)." ... 

TIPS groups have been used in different ways to prevent undesired C-2 lithiation of indoles and benzothiophenes. The introduction of a TIPS group onto 4-bromo-l/f-pyrrolo[2,3b]pyridine permitted metalation to occur exclusively at C-4, affording the 4-fluoro product (eq 16). The TIPS group was removed with TEAR Without TIPS, transmetalation at C-2 was observed. 

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