Synthetic Accesses to 3/5-pyrazole Carboxylic Acids

This review attempts to sum up all the synthetic accesses to 3/5-pyrazole carboxylic acids or esters published, or patented, in the last 120 years. Many of them have demonstrated their robustness as well as quite large scopes. However, a majority are relying on the regioselectivity of reactions such as ketones deprotonations, cyclocondensations or [2+3] cycloadditions. For this reason, the preparation of original 3/5-carboxypyrazoles featuring a structure departing from the inherent regioselectivity of these synthetic accesses could be problematic. Moreover, a large scale synthesis of some 3/5-carboxypyrazoles could be a real challenge. It is thus reasonable to forecast that even more synthetic methodologies should be reported in the future in attempts to meet such requirements.