Efficient syntheses of 2-(2,6-dichloro-4-trifluoromethyl-phenyl)tetrahydrocyclopenta, tetrahydrothiopyrano, hexahydrocycloheptapyrazoles and tetrahydroindazoles

Two methods are described for the regiospecific synthesis of 3,4-fused-cycloalkyl-1-arylpyrazoles; the key step is the reaction between aryl hydrazines and cyclic α-(dimethoxymethyl)ketones. The latter are obtained by BF3-promoted alkylation of ketones with trimethylorthoformate.