TRANSFER HYDROGENATION OF P-SUBSTITUTED ALPHA-METHYLSTYRENES AND OF 9-METHYLENEFLUORENE AS A CRITERION OF MECHANISM

The uncatalyzed transfer hydrogenation of substituted alpha-methylstyr enes with 9,10-dihydroanthracene (DHA), xanthene (XAN), or 9,10-dihydr oacridine (DHAC) was studied mechanistically. The three hydrogen donor s react at very similar rates and with similar activation parameters a nd with little discrimination between the various substituted styrenes . The kinetic isotope effects are also similar and the solvent effect is small. A hydrogen atom transfer mechanism (retrodisproportionation) is, therefore, preferred to a hydride transfer mechanism. This is sup ported by the very similar reactivity of the hydrogen transfer reactio n of DHA and XAN with 9-methylenefluorene. The product yields in all r eactions investigated in this project were >90%.