J. Org. Chem. 1989,54, 3215-3216 Registry No. 1, 61-19-8; 2-2NHS,120311-44-6; KHS05, 10058-23-8;Poly A (potassium salt), 26763-19-9.
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Comparison of the Relative Rates of Radical Addition versus Diradical Intermediate Formation in [2 21 Cycloaddition Reactions of Similarly Substituted Alkenes and Alkynes
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Daniel J. Pasto* and Wei Kong Department of Chemistry, University of Notre Dame, Notre Dame, Indiana 46556
AH
Received January 9, 1989
Numerous studies have focused on the determination of the relative reactivities of substituted alkenes and alkynes toward free-radical addition. The available data indicates that free-radical additions occur more rapidly to the substituted alkenes than to the similarly substituted alkynes. The relative reactivities for trapping R (R = n-butyl or tert-butyl generated by the reduction of RHgCl with NaBH4) are H2C=CHC02Et(1.0) and H C 4 C 0 2 E t (0.19), and H&=CHCeH5 (0.15) and H C 4 C 6 H 5 (0.02).' In a similar type of study the relative reactivities for the trapping of the cyclohexyl radical were found to be H2C=CHC02Et (6.7) and HC=tCO,Et (2.1), and H2C= CHC6H5(1.0) and HCrCC6H5 (0.25).2 The addition of substituted benzenethiyl radicals to H,C=CHCO,Et and HC=CC02Et favored the alkene by factors of 24-47.3 And finally, the rates have been measured for the gasphase addition of the methylthiyl radical to ethylene and acetylene (2.8 and
