760175-72-2Relevant academic research and scientific papers
α- and β-thujone radical rearrangements and isomerizations. A new radical clock
He, Xiang,Ortiz De Montellano, Paul R.
, p. 5684 - 5689 (2004)
Radical clocks have been extensively used in chemical and biochemical mechanistic studies. The C4 radicals of α- and β-thujone can undergo two distinct rearrangement reactions that could, in principle, serve as simultaneous but independent radical clocks. We have therefore generated these C4 radicals by photolysis of the corresponding N-hydroxypyridine-2-thione ester precursors and have investigated their fates and lifetimes. Photolysis of either α- or β-thujone generates the same 6:100 mixture of α- and β-thujone when the radicals are quenched by thiophenol. Hydrogen atom transfer from thiophenol to the radical thus occurs preferentially from the less sterically hindered α-face to give β-thujone. The third product formed in the photolysis via opening of the cyclopropyl ring is 2-methyl-5-isopropylcyclopent-2-enone. The ratio of ring opened to unopened products gives very similar values of krα = 4.4 × 10 7 S-1 and krβ = 1.0 × 108 S-1 for ring opening of the radicals generated from α- and β-thujone, respectively. If the C4 cation rather than radical is generated, it is converted to carvacrol, a phenol that is not obtained in the radical reactions. Thujone therefore differentiates between radical and cation pathways and provides a measure of the radical lifetime.
