Flash Vacuum Pyrolysis in the Synthesis of O- and N-Heterocycles.

YRANZO, G. I.; MOYANO, E. L.

Modern Approaches to the Synthesis of O- and N-Heterocycles

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Lugar: India; Año: 2006;

Flash vacuum pyrolysys (FVP) consist in applying a molecule high temperature in a short time (~10-2 s). This important feature allows getting kinetic as well as unstable products. This is an interesting methodology to study reaction mechanisms and for synthesis. Flash vacuum pyrolysis is used as a single step synthetic procedure as well as a complement of a multistep route; these reactions are normally clean, without solvent, so they normally involve carbenes, nitrenes, radicals and concerted reactions. In the first part of this chapter the main principles and applications of FVP will be described. In the second part of this chapter different reactions affording O- and N- heterocyclic compounds will be described. These reactions will be grouped by ring size and by the number of heteroatoms present in the molecules involving monocyclic and fused rings. The effect of different substituents and some kinetic results will also be described. The most common reactions that afford heterocycles are cyclisations of unsaturated compounds, ring fragmentations including Retro Diels Alder reactions, isomerisations, extrusion of small neutral molecules (SO2, CO2, N2, etc.). Flash vacuum pyrolysis of Meldrum´s acid will have a special attention as this is one of the most important routes to heterocycles.