ABSTRACT
Dialkyl 5,5'-dioxo-4,4'-bipyrazole-4,4'-dicarboxylates are readily obtained by the reaction of 5-hydroxypyrazole-4-carboxylates in refluxing thionyl chloride. The obtained diesters can be transformed into the corresponding 4,4'-bipyrazoles via alkaline hydrolysis and subsequent decarboxylation. Detailed NMR spectroscopic investigations (1H, 13C, 15N) were undertaken with all products prepared. Moreover, the structure of a representative 5,5'-dioxo-4,4'-bipyrazole-4,4'-dicarboxylate was confirmed by X-ray crystal structure analysis.
ABSTRACT
A synthesis of tetrasubstituted pyrazoles containing two, three or four pyridinyl substituents is described. Hence, the reaction of 1,3-dipyridinyl-1,3-propanediones with 2-hydrazinopyridine or phenylhydrazine, respectively, affords the corresponding 1,3,5-trisubstituted pyrazoles. Iodination at the 4-position of the pyrazole nucleus by treatment with I2/HIO3 gives the appropriate 4-iodopyrazoles which served as starting materials for different cross-coupling reactions. Finally, Negishi cross-coupling employing organozinc halides and Pd catalysts turned out to be the method of choice to obtain the desired tetrasubstituted pyrazoles. The formation of different unexpected reaction products is described. Detailed NMR spectroscopic investigations (1H, 13C, 15N) were undertaken with all products prepared. Moreover, the structure of a condensation product was confirmed by crystal structure analysis.
ABSTRACT
A synthesis of ß-oxonitriles is reported via the generation of R(1)R(2)CLiCN species followed by the trapping with variously decorated Weinreb amides. The optimization study revealed that lithiation of acetonitriles is best accomplished by deprotonation with MeLi-LiBr at low temperature. The protocol can be conveniently adapted to the synthesis of α-mono or α,α-disubstituted cyanoketones. (15)N- and (17)O-NMR data are reported for selected compounds.
