Condensation of silylhydrazines and esters into silylhydrazones and pyrazolones

Acetoacetic- and 4-oxopentanoic-acid-ethylester-N-tri(organyl)silylhydrazon es (1-4), R2R'Si-NH-N=CMe-(CH2)(n)-COOEt; 1: R = CMe3, R' = C6H5, n = 1; 2: R = CMe3, R' = Me, n = 1; 3: R = CHMe2, R' = CMe3, n = 1; 4: R = CMe3, R' = C6H5, n = 2) are obtained as cis/trans isomers by condensation of tri(org anyl)silylhydrazines and acetoacetic (1-3)- or 4-oxopentanoic-acid-ethylest ers (4). Heating 1-3 form ethanol and O-silylpyrazolones (5-7) by a 1,3-N,O -silyl group migration. Complex 7 reacts with ClSiMe3 in the presence of Et 3N in a substitution of the NH group to give 5-siloxy-3-methyl-2-trimethyls ilyl-pyrazolone, 8. In a molar ratio 2:1 the analogous reaction of 1 and Cl 2SiMe2 leads to the formation of the bis(5-siloxy-3-methy1)-1,2-diaza-3,5-c yclopentadienyl)dimethylsilane 9. The crystal structures of 5 and 9 are rep orted.