Mechanistic analysis of oxidative C-H cleavages using inter- and intramolecular kinetic isotope effects

A series of monodeuterated benzylic and allylic ethers were subjected to oxidative carbon-hydrogen bond cleavage to determine the impact of structural variation on intramolecular kinetic isotope effects in DDQ-mediated cyclization reactions. These values are compared to the corresponding intermolecular kinetic isotope effects that were accessed through subjecting mixtures of non-deuterated and dideuterated substrates to the reaction conditions. The results indicate that carbon-hydrogen bond cleavage is rate determining and that a radical cation is most likely a key intermediate in the reaction mechanism. (c) 2009 Elsevier Ltd. All rights reserved.