Formation of Santonide and Parasantonide in the Pyrolysis of Santonic Acid. A new insigth of an old reaction

MOYANO, E. L., N. M. CEBALLOS, J. ZINCZUK, E. A. RÚVEDA AND G. I. YRANZO

Arkivoc

ARKAT-USA

Año: 2005 vol. XII p. 352 - 362

1424-6376

Thermal reactions of santonic acid (1) in solution and flash vacuum pyrolysis were carried out in order to study the mechanism of formation of parasantonide (3) and santonide (4). Heating an acetic acid solution of 1 in a sealed tube at 200ºC led to 3, while heating at 175 ºC afforded 4. Flash vacuum pyrolysis of 1 was carried out between 300 and 550 ºC, 10-2 torr and contact times of 10-2s. Results showed that 1 decomposed by at least two different mechanisms. One involving isomerization and lactonization affording 4 which affords 3 and the other involving radical scission and formation of aromatic and conjugated products. A mechanism involving isomerization to isosantonic acid (6) previous to lactonization is proposed for formation of 4.