Carbon-13 NMR study of 1-methyl-3-phenyl-4-diazo-5-benzoylamidopyrazole and other model pyrazole compounds
A 13C nmr study of a diazo, of two diazonium salts and of some other model pyrazole compounds is reported. It is found that the C-4 diazo carbon is more shielded than the normal sp2 pyrazole hybridized carbon, while its diazonium salt is more deshielded. The electron density on the C-4 of the diazopyrazole is probably due to the positive charge on the terminal nitrogen. Thus the 13C chemical shift values allowed us to understand the chemical behaviour of a compound of potential antitumor activity.
Spiro-compounds [e.g., (8), (13)] that resemble the four central rings of the antitumour agent fredericamycin A have been synthesized by methods that are based on (i) intramolecular acylation and high-pressure Diels–Alder chemistry [(5)→(8)] or (ii) radical spiro-cyclization [e.g., (11)→(13)].