Dihalodiazirines and the photochemical generation of dihalocarbenes: new light on old problems

The Graham oxidation of amidines to halodiazirines, coupled with the diazirine exchange reaction, makes available many new diazirine precursors of carbenes. Nitration of the phenoxy moieties of phenoxychloro- or phenoxyfluorodiazirine converts them to leaving groups, ultimately permitting the preparations of CCl2, CCIF, and CF2. Absolute rate constants and activation parameters are measured for the additions of these carbenes to several alkenes. The comparative contributions of Delta H double dagger and Delta S double dagger to Delta G double dagger are assessed for these reactions, as are the dependences of Delta H double dagger and Delta S double dagger on the structures and reactivities of the carbenes and alkenes. Copyright (C) 2009 John Wiley & Sons, Ltd.