Trapping of Cyclopentanediyl and Trimethylenemethane Triplet Diradicals with the Nitroxide 1,1,3,3-Tetramethyl-1,3-dihydroisoindolin-2-yloxyl

Article abstract of DOI:10.1021/jo00029a036

Nitroxide trapping constitutes a convenient and effective alternative to dioxygen for the detection of triplet diradical intermediates.Thus, photolysis of the azoalkanes 1a-c in the presence of the nitroxide 1,1,3,3-tetramethyl-1,3-dihydroisoindolin-2-yloxyl produced the bisalkoxyamines 3a-c by trapping of the transient triplet diradicals 5a-c.The resulting bis-adducts 3a-c were fully characterized, and their regio- and stereochemistry were established on the basis of spectral and X-ray data for trans-3a and trans-3b.The novel bis-azoalkane 1d was prepared andits photochemical loss of nitrogen studied in the presence of the above nitroxide or dioxygen as scavengers.In the case of the nitroxide, the tetrakis adduct 3d was obtained, tentatively assigned in view of its thermal instability, while with dioxygen the stable bis-peroxide 4d was isolated and rigorously characterized.Instead of concurrent double denitrogenation to afford the high-spin non-Kekule species 5d or its low-spin quinoid diradical 5d', stepwise loss of dinitrogen and trapping is proposed to be the pathway to these products.