Competition studies and the relative reactivity of enol ether and allylsilane coupling partners toward ketene dithioacetal derived radical cations

The relative reactivity of enol ether and allylsilane trapping groups toward a ketene dithioacetal derived radical cation has been examined with the use of competition and cyclic voltammetry studies. The competition studies pit the olefinic trapping groups against an alcohol trapping group under conditions of both kinetic and thermodynamic control. With the enol ether trapping group, the chemoselectivity of the competition study favored C-C bond formation under all conditions. With the allylsilane trapping group, the chemoselectivity of the competition study favored C-O bond formation under all conditions. Cyclic voltammetry data was used to show that allylsilane trapping of the radical cation is much slower than enol ether trapping of the radical cation. However, the inefficiency of the allylsilane trapping reaction could not be attributed solely to a slow cyclization. Rather, it appears that a slow second oxidation step plays a role in determining the yield of the reaction. (C) 2015 Elsevier Ltd. All rights reserved.