1,4-C,H INSERTION OF VINYL VINYLIDENE TO INTERMEDIATE CYCLOBUTADIENE DOES NOT OCCUR DURING FLASH VACUUM PYROLYSIS OF 1-BUTEN-3-YNE

1-Buten-3-yne (1) and [4-D]1-buten-3-yne (1a) have been treated between 800 and 1000 degrees C under flash vacuum pyrolysis as well as under gas phase pyrolysis in nitrogen and the effluents thoroughly analyzed by GC, GC/MS, GC/FTIR H-1- and H-2-NMR spectroscopy. Since no evidence for a D-shift in In from the acetylenic to the olefinic position could be detected, the formation of cyclobutadiene as a highly reactive species from the intermediately generated vinyl vinylidene has to be excluded.