Mechanistic studies on PET-oxidative cyclization of unsaturated silyl enol ethers:: dependence of the regioselectivity on alcohol addition and pressure effects

Unsaturated silyl enol ethers are irradiated in the presence of electron transfer sensitizers. The efficiency of the cyclization reaction using different sensitizers is investigated. The endolexo regiochemistry of the ring closure reaction can either be controlled by variation of the silyl group or by addition of alcohol. Furthermore, a dependence of the regiochemistry on pressure is revealed and it seems that it can be related to acetonitrile acting as a nucleophile at 1500 bar. As key intermediates radical cations and radicals are involved.