CONFORMATION OF 2-ALKOXYTETRAHYDROPYRAN-2-YL RADICALS

Molecular conformation has a profound effect on the rates of hydrogen atom abstraction from 2-alkoxytetrahydropyrans.4, 5 For example,4 hydrogen abstraction from the conformationally biased6-8 (anancomeric9) 2-methoxy-4-methyl-tetrahydropyrans by triplet benzophenone at ambient temperature occurs ~8 times as rapidly from the cis isomer as from the trans isomer. Since both isomers gave the same product distribution it was concluded4 that a common free radical was formed.10 We now report an EPR study which establishes that 1 and 2 yield a common radical even at temperatures as low as -120 °C and that this radical is probably cis-2-methoxy-6-methyltetrahydropyran-2-yl (3). Similarly, hydrogen abstraction from cis-and frans-2-ethoxy-4-methyltetrahydropyrans (4 and 5, respectively) yields a common radical which is probably cis-2-ethoxy-4-methyltetrahydropyran-2-yl (6). © 1979, American Chemical Society. All rights reserved.