Thermal pericyclic tandem reactions

Gas phase thermal isomerizations of twelve acetylenic systems, all of which can in principle undergo two successive pericyclic steps, are described. T he substrates, the syntheses and spectroscopic properties of which are pres ented, are formal derivatives of but-2-yne, with different functional group s in the 1- and the 4-positions. The Cope, Claisen, Claisen ester, retro-en e, 1,5-hydrogen shift, and 1,5-homo hydrogen-shift processes were employed as the pericyclic steps from which the tandem processes were composed. The compositions of the pyrolysates obtained were determined over broad tempera ture ranges, and the mechanisms of the individual steps producing the pyrol ysis products are discussed.