Acetaldehyde → 1-(2-Chloropyridin-3-yl)ethanol

Participants

Reaction Steps

Scheme 1 describes a method for preparation of 1H-pyrazolo[3,4-b]pyridine derivatives (XVI) by reacting the 3-anion of 2-chloropyridine (I) with acetaldehyde to form 1-(2-chloropyridin-3-yl)ethanol (II). The alcohol is then oxidized to (III) before cyclizing in the presence of hydrazine to 3-methyl-1H-pyrazolo[3,4-b]pyridine (IV). The methyl is oxidized and esterified to methyl 1H-pyrazolo[3,4-b]pyridine-3-carboxylate (VI). The ester (VI) is treated with bromine to form methyl 5-bromo-1H-pyrazolo[3,4-b]pyridine-3-carboxylate (VII) before hydrolyzing the ester to acid VIII. Acid VIII was reacted with N,O-dimethylhydroxylamine to form the Weinreb amide (IX). After protection of the 1H-pyrazolo[3,4-b]pyridine NH, the Weinreb amide is reduced to aldehyde XI. 5-substituted 1H-pyrazolo[3,4-b]pyridine-3-carbaldehyde derivatives (XIII) are prepared by Suzuki Coupling of 5-bromo-1-(tetrahydro-2H-pyran-2-yl)-1H-pyrazolo[3,4-b]pyridine-3-carbaldehyde (XI) with various boronic acid derivatives (XII). Aldehyde XIII is reacted with various substituted and unsubstituted aryl/heteroaryl-3,4-diamines (XIV) to form XV. Final deprotection of the pyrazolone nitrogen yields the desired 1H-pyrazolo[3,4-b]pyridine derivative (XVI).

Provenance & Evidence