Radical clock reactions under pseudo-first-order conditions using catalytic quantities of diphenyl diselenide. A Se-77- and Sn-119-NMR study of the reaction of tributylstannane diphenyl diselenide

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 Bu(3)SnH. Using this method the rate constant for cyclization of the 6,6-diphenyl-5-hexenyl radical was found to be 6.8 x 10(7)s(-1) at 20 degrees C, in fair agreement with the literature value of 4 x 10(7)s(-1). An extension of the method was used to determine the rate of quenching of the 2,3,4,6-tetra-O-acetoxy-l-glucosyl radical by PhSeH as 3.6 x 10(6)s(-1) at 78 degrees C. The reaction of Bu(3)SnH and PhSeSePh was studied by a combination of Se-77- and Sn-119-NMR spectroscopy.