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Laser-flash photolysis methods were used to determine Arrhenius functions for cyclizations of the 4,4-diphenyl-3-butenyl (2) and trans-4-phenyl-3-butenyl (5) radicals to the 1,1-diphenylcyclopropylcarbinyl (1) and 1-phenylcyclopropylcarbinyl (4) radicals, respectively. At 20 °C, the cyclization rate constants are 1.7 × 107 and 5.4 × 106 s-1. Equilibrium constants for the two processes were estimated and evaluated with thermochemical data and via computational methods, and Arrhenius functions for the ring-opening reactions of the cyclopropylcarbinyl radicals were calculated. The cyclization reactions of 2 and 5 are strongly enthalpy controlled. Production of radicals 1 and 2 from the corresponding tert-butylperoxy esters in the presence of Et3SnH gave diphenylcyclopropylmethane and 1,1-diphenyl-1-butene from H-atom trapping of radicals 1 and 2 and 4-phenyl-1,2-dihydronaphthalene which derives from the product radical formed by addition of the radical moiety in 2 to the cis-phenyl group. Rate constants for the latter cyclization of 2 and for reactions of radicals 1 and 2 with Et3SnH were obtained from the indirect kinetic studies.

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PTOC oxalates (anhydrides of an oxalic acid monoester and N-hydroxypyridine-2-thione) were used in laser flash photolysis (LFP) kinetic studies. Irradiation of the PTOC oxalates gave the following alkoxycarbonyl radicals ROC(·)O:  2a, R = PhCH2; 2b, R = (trans-2-phenylcyclopropyl)methyl; 2c, R = (2,2-diphenylcyclopropyl)methyl. Rate constants for decarboxylation of radical 2a measured by LFP were in agreement with those obtained previously by indirect kinetic methods. Rate constants for decarboxylation of radical 2c were measured by LFP over the temperature range 3−48 °C; the reaction is described by log k = 12.2−9.6/2.3RT (kcal/mol). Reactions of Bu3SnH with radical 2c produced from the corresponding phenylseleno carbonate gave inconsistent kinetic results apparently due to the production of small amounts of PhSeH that reacted rapidly with 2c. An approximate rate constant at 2 °C for reaction of Bu3SnH with 2c produced from the PTOC oxalate was obtained. Tin hydride reacts with the alkoxycarbonyl radical approximately 1 order of magnitude less rapidly than it reacts with alkyl radicals. Rate constants for 5-exo cyclizations of simple alkoxycarbonyl radicals were estimated from previous results and the approximate rate constant for tin hydride trapping; the cyclizations are slightly faster than 5-exo cyclizations of structurally related alkyl radicals.