Photochemical Addition of Tertiary Amines to Stilbene. Free-Radical and Electron-Transfer Mechanisms for Amine Oxidation

Article abstract of DOI:10.1021/ja00371a022

Several amines of structure Me2NCH2R, where R = CH=CH2, CO2Et, CCCH3, and CCH, but not Ph, react with the singlet state of trans-stilbene in hexane solution to yield adducts of structure PhCH2CHPhCHRNMe2.In acetonitrile solutions, these adducts are accompanied by variable amounts of adducts of structure PhCH2CHOPhCH2NMeCH2R.Both types of adduct are formed by cross combination of 1,2-diphenylethyl-α-aminoalkyl radical pairs.The mechanism of radical pair formation is concluded to be solvent dependent.In nonpolar solvents, hydrogen atom transfer selectively yields a merostabilized α-aminoalkyl radical.In polar solvents, a sequential electron-transfer, proton-transfer mechanism yields both α-aminoalkyl radicals.