1-Piperidinecarboxaldehyde → 5-Bromo-2-fluoro-3-pyridinecarboxaldehyde

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반응 단계

Scheme 3 describes a method for preparation of 3-(1H-indol-2-yl)-1H-pyrazolo[3,4-b]pyridine derivatives (XXVII) by first selective deprotonation at position-3 of 5-bromo-2-fluoropyridine (XVII) with LDA followed by N-formylpiperidine quench to produce 5-bromo-2-fluoronicotinaldehyde (XVIII). Aldehyde XVIII was condensed with pinacol followed by nucleophilic aromatic substitution by hydrazine to give 5-bromo-2-hydrazinyl-3-(4,4,5,5-tetramethyl-1,3-dioxolan-2-yl)pyridine (XIX). XIX was then cyclized under acidic conditions to yield 5-bromo-1H-pyrazolo[3,4-b]pyridine (XX). The 1H-pyrazolo[3,4-b]pyridine NH was THP protection followed by reaction of the bromide (XXI) with bis(pinacolato)diboron to form the borate ester (XXII). Suzuki coupling with various bromides (XVIII) or chlorides yields 1H-pyrazolo[3,4-b]pyridine derivatives (XXIII). Iodization of position-3 of 1H-pyrazolo[3,4-b]pyridine (XXIII) with N-iodosuccinimide followed by Suzuki Coupling with various Boc-protected 1H-indol-2-ylboronic acids (XXV) to produce (XXVI). Final deprotection of the pyrazole and indole nitrogens yields the desired 3-(1H-indol-2-yl)-1H-pyrazolo[3,4-b]pyridine derivatives (XXVII).

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