Practical multigram synthesis of 4- and 5-pyrazolylacetic acids

A practical synthesis of pyrazolylacetic acids has been developed using oxalic acid derivatives as C2 building blocks, followed by Wolff-Kishner-Huang Minlon reduction. Two complementary approaches were optimized: H/Li exchange at the 5-position with diethyl oxalate addition, and direct electrophilic acylation at the 4-position with ethyl 2-chloro-2-oxoacetate. The protocols were scaled to 300-500 g, affording products in ca. 20% overall yield. A simplified "fast" protocol sacrifices yield for practicality, delivering products without the need for intermediate purification. The scope includes various alkyl-, phenyl-, pyridyl-, and bromo-substituted pyrazoles, as well as N-Boc-protected derivatives. Extension to 1-methyl-1H-1,2,3-triazole demonstrates potential applicability to other heterocyclic systems. These methods offer preparative advantages over previously employed approaches for multigram-scale synthesis.