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Intermediates in the von Pechmann Reaction

Nowakowska E. M., Zaleski J., Kyzio J. B.

Polish Journal of Chemistry

2008

Vol. 82, nr 7

1399-1399

Condensation of meta-cresol with ethyl acetoacetate in dehydrated phosphoric acid is slow enough to observe formation and disappearance of the in termediates viz 1,2- di -hydro-4,7-dimethyl-4-(4-hydroxy-2-methylphenyl)-coumarin (3) and 1,2- di hydro- 4,7-dimethyl-4-(2-hydroxy-4-methylphenyl)-coumarin (4). GCMS analyses of the reaction mixtures indicated that 4,7-dimethylcoumarin (5) was formed from 3 and 4 by elimination of meta-cresol molecule. The compounds 3 and 4 were isolated by the column chromatography. Their structures were elucidated by the spectroscopic methods but unequivocal assignment of the structure to the particular isomer was not possible. The structures were resolved by X-ray diffraction studies.

Structure and Rearrangement of Ring Substituted N0Methyl-N-phenylnitramines

Daszkiewicz Z., Zaleski J., Nowakowska E. M., Kyzioł J. B.

Polish Journal of Chemistry

2002

Vol. 76 / nr 8

1113-1125

The mechanism of the acid catalyzed nitramine rearrangement must account for the unusual sensitivity of the reaction of N-methyl-N-phenylnitramine derivatives to the ring substituents. Spectral analyses indicate the lack of interaction between the nitramino group and the second substituent through the aromatic ring. X-ray analyses confirm the spectral data: there is no conjugation between the aromatic and nitramine sextets of _-electrons. X-ray structural data also indicate that the nitramino group cannot behave as the basic centre. A reconsideration of the rearrangement rate constants of the series of ring substituted N-methyl-N-phenylnitramines lead to the conclusion that migration of the N-nitro group precedes protonation. The influence of the substituents on the reaction rates is determined by their influence on the basicity of the imino nitrogen in an intermediate. The CIDNP effect, observed in the rearrangement, results from the transformation of mobile nitrito group into the stable nitro substituent.