Gerhard Hojas

Malonates in Cyclocondensation Reactions

The use of malonates such as diethyl malonates 9, (chlorocarbonyl)ketenes 15 and bis(2,4,6-trichlorophenyl) malonates 18 as reagents for cyclocondensation with 1,3-dinucleophiles to give six-membered heterocycles is described. Further attempts to use malonates such as bis(trimethylsilyl) malonates 19 and bis(carbamimidoyl) malonates 29 as new cyclocondensation agents are described .

Study of the thermal behavior of azidohetarenes with differential scanning calorimetry.

Thermal properties of azidohetarenes without reactive ortho-substituents, obtained by DSC analysis, were compared with the DSC data of ortho-phenyl and ortho-acyl substituted azidohetarenes, which give ring closure reactions either to indoles or to five-membered heterocycles such as isoxazoles. The reaction temperatures and reaction enthalpies give both information to prepare the reaction conditions and important safety information and were, in addition, used to find out relations between the temperatures or enthalpies with the three different reaction mechanisms.

Synthesis of 4-azido-3-diazo-3H-pyrazolo[3,4-b]quinoline from 3-amino-4-hydrazino-1H-pyrazolo[3,4-b]quinoline

The reaction of 3-amino-4-hydrazino-1H-pyrazolo[3,4-b]quinoline 8 with nitrous acid did not give 2,4-diazidoquinoline-3-carbonitrile 5 as reported previously, but afforded in 60% yield 4-azido-3-diazopyrazolo[3,4-b]quinoline 10, which gave by azo coupling with 2-naphthol 4-azido-3-(2-hydroxy-1-naphthylazo)-1H-pyrazolo[3,4-b]quinoline 11.

Thermal Cyclization of 3‐Acyl‐4‐azidopyridines to Isoxazolo[4,3‐c]pyridines

4-Azidopyridines such as 3-acetyl-4-azido-2-pyridones 3 or 4-azido-3-ethoxycarbonylpyridine 7 with reactive ortho-acyl substituents were obtained from the 4-hydroxy-2-pyridones 1, resp. 5via 4-tosyloxy-2-pyridones 2 or the 2,4-dichloropyridine 6. DSC-assisted thermolysis of the azides 3 and 7 resulted in electrocyclization and elimination of nitrogen to the isoxazolo[4,3-c]pyridines 4 and 8.