Markéta Svobodová

Structure and tautomerism of azo coupling products from N-alkylenaminones derived from acetylacetone and benzoylacetone in solid phase and in solution

A series of azo coupling products have been prepared by reaction of substituted benzenediazonium tetrafluoroborates with N-alkyl 4-aminopent-3-en-2-ones or 3-amino-1-phenylbut-2-en-1-ones. The structure and tautomerism of the reaction products were studied by means of single-crystal X-ray study and by NMR spectroscopy in deuteriochloroform solution. The azo coupling products obtained from 4-methylaminopent-3-en-2-ones (3a–i) exist in CDCl3 solution as E/Z isomer mixtures with the Z isomer strongly predominating. The major isomer is a mixture of enamino–azo and imino–hydrazo tautomers with the former predominating. The proportion of the azo form depends on substitution of the benzene ring of the diazonium salt and decreases in the order of MeO > Me > Br > NO2. The position of tautomeric equilibrium is practically unaffected by switching from 4-methylaminopent-3-en-2-ones to 3-methylamino-1-phenylbut-2-en-1-ones. In the solid phase, the azo form always predominates; substitution of diazonium salt and at N3 nitrogen does not significantly affect the position of the tautomeric equilibrium. The azo coupling products always exist in the form of a single Z isomer. All determined structures, in the solid state, consist of a mixture of the two tautomeric forms, amino–diazenyl and imino–hydrazone, in ratios ranging from 82/18 to 91/9%. The weighed superimposition of both the hydrogen-bonded N1N2–C1C2–N3H/ HN1–N2C1–C2N3 heterodienic fragments, however, do not allow to clarify the effects of the para-substituents at the N1-phenyl ring both on the N1⋯N3 hydrogen-bond distances and on the bond lengths in the heterodienic systems within the series 3a–c,f and 4a–c,e,f.

A simple, enaminone-based approach to some bicyclic pyridazinium tetrafluoroborates

Summary Easily obtainable cyclic enaminones (piperidin-2-ylidenealkanones) can be transformed into substituted bicyclic pyridazinium tetrafluoroborates upon treatment with corresponding diazonium salts. The transformation can be performed either in a one-pot way or in a two-step process with the isolation of single azo-coupled enaminone as the intermediate. The former method is superior. Under the optimized conditions, a number of pyridazinium salts substituted with both electron-donating and electron-withdrawing substituents was easily synthesized. A mechanism of the formation of the pyridazinium salts is suggested. A partial drawback is the possibility of the formation of a mixture of products when using a different diazonium salt in each step due to a reversibility of the azo coupling. This can be suppressed by using a more reactive diazonium salt before a less reactive one.

Coordination Compounds Based on 1,2,3,4-Tetrahydro-isoquinoline-3-carboxylic Acid

Syntheses of 2,6-bis[((3S)-3-(methoxycarbonyl)-1,2,3,4-tetrahydroisoquinolin-2-yl)carbonyl]pyridine and its coordination compounds with Cu2+, Co2+, Co3+, or Fe3+ are described. By means of 1H- and 13C-NMR spectra it was proved that 2,6-bis[((3S)-3-(methoxycarbonyl)-1,2,3,4-tetrahydroisoquinolin-2-yl)carbonyl]pyridine as well as its coordination compound with Co3+ exist in the form of a mixture of three conformers, differing in the conformations at the two amide groups present. The prepared coordination compounds were tested in the enantioselective catalysis of the nitroaldol addition of nitromethane with 2-nitrobenzaldehyde or 4-nitrobenzaldehyde, and in the Michael addition of ethyl 2-oxocyclohexanecarboxylate to but-3-en-2-one.