PHOTOCHEMICAL REARRANGEMENTS OF DIAZIRINES AND THERMAL REARRANGEMENTSOF CARBENES

Trans-3-(2-tert-butylcyclopropyl)-3H-diazirine was decomposed both the rmally and photochemically to give the anticipated ring-expanded 3-ter t-butylcyclobutene product, along with azine and products of trapping by solvent. In the presence of tetramethylethylene (TME), a bicyclopro pane adduct was formed The yield of 3-tert-butylcyclobutene product, h owever, is only very slightly (0-7%) decreased upon increasing the con centration of TME. Thus there must be two product-forming pathways. On e pathway is a relaxed carbene intermediate, the second with the excit ed singlet state of the diazirine precursor. It is posited that upon a ctivation diazirines open to form a diazirinyl diradical which undergo es the following processes: a) ring closure to reform the diazirine, b ) formation of the linear diazo compound, c) cleavage to form carbene and dinitrogen, d) rearrangement Ito cyclobutene in concert with nitro gen extrusion.