Highly Efficient Dehydrogenation of 5-Benzyl-3-phenyl-2-thioxoimidazolidin-4-one: Microwave versus Flash Vacuum Pyrolysis Conditions

5‐Benzyl‐3‐phenyl‐2‐thioxoimidazolidin‐4‐one underwent thermal dehydrogenation to afford 5‐benzylidene‐2‐thioxoimidaxolidin‐4‐one under microwave and flash vacuum pyrolysis conditions. A high predominance of the Z‐isomer over the E‐isomer of the imidazolidinone product was achieved. By using DFT and NBO calculations, the mechanism of the dehydrogenation and the selectivity were also explored. In this article we report the dehydrogenation reaction of a benzylthioxoimidazolidinone derivative by using two unconventional and solvent‐free methodologies: flash vacuum pyrolysis and microwave‐induced pyrolysis. DFT calculations were performed to understand the dehydrogenation mechanism and to explain the high selectivity achieved towards the formation of the Z‐isomer.