A method for the flash vacuum thermolysis of non-volatile compounds

Flash (Vacuum) Pyrolysis Apparatus and Methods

The history of pyrolysis equipment, methods, and reactions is narrated in the Introduction. Detailed descriptions of flash vacuum pyrolysis (FVP) (or thermolysis, FVT) apparatus for preparative and spectroscopic (UV, IR, electron spin resonance) purposes with product isolation at 77 K or in Ar matrices at ~10 K are presented. Very low pressure pyrolysis (VLPP), laser pyrolysis, and pulsed pyrolysis (jet flash pyrolysis) are also described together with illustrations of apparatus. The solvent spray flash vacuum pyrolysis (SS-FVP) of liquids or solutions of compounds of low volatility is described together with methods for the addition of solids to a pyrolysis tube, in particular details of pipto-pyrolysis (‘falling solid pyrolysis’). Methods used for catalytic vacuum gas–solid reactions (VGSR) are also summarised.

Intramolecular Diels-Alder Reaction of N-Alkyl-2-cyano-1-azadienes: A Study of the Eschenmoser Cycloreversion of Dihydrooxazines as a Route to N-Alkyl-2-cyano-1-azadienes

In connection with the development of the intramolecular Diels-Alder reaction (IMDA) of 1-azadienes, the 5,6-dihydro-4H-1,2-oxazine 12has been evaluated as a synthon equivalent of the 2-cyano-1-azadiene system. It was found that the dihydrooxazonium salt 27, generated in situ from the cyclic hydroxamic acid derivative 26, is converted directly to azadiene 4a via tautomerization to the corresponding enamine and a particularly facile Eschenmoser type cycloreversion process. Conditions were subsequently found for the preparation of synthon 12. N-Alkylation of this intermediate with alkyl bromides in the presence of Ag(+) ion also resulted in direct formation of the 2-cyano-1-azadiene products 38a-dand 4a. Microwave irradiation of a benzene solution of azadiene 4a proved to be a convenient means to effect its IMDA conversion to indolizidine 5a. To avoid decomposition of azadiene 38c, its intramolecular cycloaddition giving 40 (60%) was achieved by flash vacuum thermolysis.