Radical Clock Reactions under Pseudo-First-Order Conditions Using Catalytic Quantities of Diphenyl Diselenide. A ⁷⁷Se- and ¹¹⁹Sn-NMR Study of the Reaction of Tributylstannane and Diphenyl Diselenide

Abstract

A method for the trapping of alkyl radicals by constant, catalytic quantities of PhSeH as a clock reaction in radical kinetics is presented. PhSeH is introduced in the form of PhSeSePh and regenerated by slow addition of a stoichiometric quantity of Bu3SnH. Using this method the rate constant for cyclization of the 6,6-diphenyl-5-hexenyl radical was found to be 6.8 × 107 s-1 at 20 °C, in fair agreement with the literature value of 4 × 107 s-1. An extension of the method was used to determine the rate of quenching of the 2,3,4,6-tetra-O-acetoxy-1-glucosyl radical by PhSeH as 3.6 × 106 s-1 at 78 °C. The reaction of Bu3SnH and PhSeSePh was studied by a combination of 77Se- and 119Sn-NMR spectroscopy.