Photoaddition Reactions of Acenaphthylenedione with α-Silyl n-Electron Donors via Triplet Single Electron Transfer-Desilylation and Triplet Hydrogen Atom Abstraction Pathways

Article abstract of DOI:10.1021/jo00031a020

Studies have been conducted to explore single electron transfer (SET) induced photoaddition reactions of acenaphthylenedione (ACND) with the n-electron donors Et2NCH2SiMe3, n-PrSCH2SiMe3, EtOCH2SiMe3, EtCO2CH2N(CH2Ph)CH2SiMe3, and EtCO2CH2N(CH2Ph)CH3.Photoaddition of α-silyl amine Et2NCH2SiMe3 to ACND occurs in CH3OH and CH3CN to produce 2-hydroxy-2-<(diethylamino)methyl>acenaphthylen-1-one.In contrast, photoaddition of n-PrSCH2SiMe3 to ACND generates two photoadducts, 2-hydroxy-2-<(n-propylthio)methyl>acenaphthylen-1-one and 2-hydroxy-2-<(n-propylthio)(trimethylsilyl)methyl>acenaphthylen-1-one, along with a ACND photoreduction dimer.Photoaddition of EtOCH2SiMe3 to ACND produces two diastereomers of 2-hydroxy-2-acenaphthylen-1-one along with the reduction dimer.The formation of all photoproducts in these photoreactions is quenched by oxygen, indicating that the triplet of ACND is the reactive excited state.Based on a consideration of the oxidation potentials of the α-silyl n-electron donors, and the nature of photoproducts, mechanisms for these photoadditions involving triplet SET-desilylation and triplet H atom abstraction pathways are proposed.Photoaddition of EtCO2CH2N(CH2Ph)CH2SiMe3 to ACND provides two major products, 2-hydroxy-2-<methyl>acenaphthylen-1-one and 2-hydroxy-2-<amino>carbethoxymethyl>acenaphthylen-1-one along with several minor products.The formation of the major products via sequential SET-deprotonation pathways shows that the electron-withdrawing carbethoxy substituent serves to control the regioselectivity for deprotonation of the amine radical cation intermediate.Results obtained from the study of the photoaddition of the non-silicon-containing amino ester, EtCO2CH2N(CH2Ph)CH3, also demonstrate the effect of electron-withdrawing carbethoxy substitutent on amine radical cation deprotonation regiochemistry.