Karel Huml

A study of photochromic sydnones: structure of the sydnone ring

Abstract The chemical structure of the sydnone ring O(1)-N(2)-N(3)-C(4)-C(5) is discussed using X-ray structural data and results of theoretical calculations obtained by the INDO method. The ring is semiaromatic, the N(2)-N(3)-C(4)-C(5) part being conjugated. The exocyclic C(5)-0(6) bond is close to a double bond and participates in the conjugation.

Studies in quinoxaline series. Part 18. Structure of products of a new reaction of tetrazolo[1,5-a]quinoxaline 5-oxide with carbanions. X-Ray molecular structure of 4-acetyl-4-methyl-3b,4-dihydroazirino[1,2-a]tetrazolo-[5,1-c]quinoxaline

Tetrazolo[1,5-a]quinoxaline-5-oxide 4 reacts with the carbanions of β-diketones and β-keto esters to give enaminoketones and enamino esters, respectively. The N-oxide 4 reacts with 3-methyl- and 3-ethyl-pentane-2,4-dione under similar conditions to give a racemic mixture of the derivatives of aziridinotetrazoloquinoxaline 10 and 11. Their structure and the trans configuration of hydrogen atom and methyl group on the aziridine ring of compound 10 were estimated by means of 1H and 13C NMR spectroscopy, and were in accord with the results of X-ray diffraction measurements, which also provided bond lengths, and valence, torsion, and dihedral angles.