New development of reactive intermediate chemistry: A case study of singlet biradicals

Singlet biradicals are key intermediates in processes involving homolytic bond-cleavages and bond formations. In general, the reactive intermediates are quite short-lived, and thus, largely elusive. To understand experimentally the reactivity, it is dispensable to pull down the singlet state below the triplet state and elongate the lifetime of singlet states. This paper describes that (1) substituent and atom effects on the ground state spin-multiplicity of cyclopentane-1, 3-diyls, (2) generation of long-lived singlet 2, 2-dialkoxycyclopentane-1, 3-diyls, and (3) the intermolecular reactivity of the singlet biradicals.