Kinetics and Mechanism of Criss-cross Cycloaddition of 1,4-Disubstituted 1,4-Diazabuta-1,3-dienes With Potassium Isocyanate and Isothiocyanate

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Authors

POTÁČEK Milan VERNER Jiří HANUSEK Jiří

Year of publication 2003
Type Article in Proceedings
Conference Book of Abstracts
MU Faculty or unit

Faculty of Science

Citation
Field Organic chemistry
Keywords criss-cross; cycloaddition; kinetic; glyoxalimine; aromatic
Description In our previous work we have dealt with the synthesis1 of 1,4-disubstituted-5-thioperhydroimidazo[4,5-d]imidazol-2-ones by one pot criss-cross cycloaddition of 1,4-disubstituted 1,4-diazabuta-1,3-dienes (glyoxalimines) with potassium isocyanate and isothiocyanate in glacial acetic acid (Scheme). Although the phenomenon of criss-cross cycloaddition reactions is known for a long time (first reported by Bailey2 in 1917) almost no kinetics study of this type of reaction have been done and only suggestions for reaction mechanism can be found in the literature3,4. Therefore we have focused our attention on kinetics and mechanism of reaction mentioned above. It was found that the observed rate constant increases linearly with the concentration of KNCX (X = O,S) and the slope is giving bimolecular rate constant k which varies from 6.7 to 36.6 l.mol.s-1 depending on substitution at benzene ring. From slopes of Hammett correlation (positive value for KNCS and negative for KNCO) it is evident that reaction is strongly affected by nucleophilicity of NCX anion.
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