Synthesis of 1-hetaryl-2,2-difluorocyclopropane-derived building blocks: the case of pyrazoles

An approach to 1-hetaryl-2,2-difluorocyclopropane building blocks compatible with the current criteria of lead-oriented synthesis was developed and implemented for the case of 3-, 4- and 5-subsituted pyrazole derivatives. The method implied 6–9 synthetic steps, including difluorocyclopropanation with the TMSCF₃–NaI system as the key transformation, and provided the title compounds on up to gram scale. The scope of the procedures towards substitution in the pyrazole ring and typical functional groups (i.e. COOH, NH₂, CH₂NH₂, CH₂OH) was established. The results obtained allowed formulation of preliminary guidelines for the synthetic feasibility of various functionalized 1-hetaryl-2,2-difluorocyclopropanes.