Flash Vacuum Pyrolysis of Isopropylidene Aminomethylenemalonates

Flash vacuum pyrolysis (at 10 5-10 3 torr and 370-800°C) of isopropylidene aminomethylenemalonate gave a wide variety of products, and the mechanism of this reaction was investigated by several authors. 

Wentrup et al. demonstrated the formation of imidoylketene (1214), methyleneketene (1215), and ethynamine (1216) during the flash vacuum pyrolysis (10-5 torr) of isopropylidene aminomethylenemalonate by collision activation mass spectroscopy and 1R spectroscopy (88JA1337). The imidoylketene (1214) appeared first at a pyrolysis temperature of 390°C. As the temperature was increased, the imidoylketene (1214) was rapidly converted into methyleneketene (1215). The formation of ethynamine (1216) was prominent in the temperature range 680-740°C, and it was accompanied by a sharp decrease in the signal of methyleneketene (1215), whereas the imidoylketene (1214) was less affected. Compounds 1214-1216 were stable at -196°C, but they polymerized on warm-up. 

McNab and his co-workers reported that the pyrolysis of monosubsti- 

Wentrup and co-workers also studied the flash vacuum pyrolysis of isopropylidene (monosubstituted amino)methylenemalonates (84JOC-2772). The pyrolysis of isopropylidene phenylaminomethylenemalonates (1223) between 400 and 600°C under a pressure of 10 5-10 3 torr afforded 4-hydroxyquinolines (1226) in 57-66% yields. The intermediates (1224 and 1225) of the pyrolysis of isopropylidene phenylaminomethylenemalonates (1223) could be isolated at - 196°C on KBr or BaF2 windows in a special apparatus allowing direct IR spectroscopic examination of the pyrolysates 

The preparative pyrolyses of aliphatic and cycloaliphatic aminomethy-lenemalonates (1231) afforded enaminoacroleins (1232) in 44-91% yields (84JOC2772). 

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