SINGLE ELECTRON-TRANSFER PROMOTED PHOTOCYCLIZATION REACTIONS OF (AMINOALKYL)CYCLOHEXENONES - MECHANISTIC AND SYNTHETIC FEATURES OF PROCESSES INVOLVING THE GENERATION AND REACTIONS OF AMINE CATION AND ALPHA-AMINO RADICALS

Mechanistic and synthetic aspects of the SET-induced photocyclization reactions of a series of alpha-, beta-, and gamma-(aminoethyl) cyclohexenones have been explored. These investigations have provided results that demonstrate that both direct (in MeOH) and SET-sensitized photocyclization reactions of members of this series containing N-(trimethylsilyl)methyl substituents serve as highly efficient methods for preparation of both fused and spiro N-heterobicyclic systems. In addition, as observed earlier, the solvent has been shown to play an important role in governing the chemoselectivity (i.e., amine cation radical desilylation vs deprotonation) of these photocyclizations. Specifically, desilylation is preferred in the polar protic solvent MeOH while deprotonation is favored in the aprotic MeCN. The results also show that the kinetic acidities of amine cation radicals, as judged by photoproduct distributions from reactions conducted in MeCN, are governed in a predictable way by substituents that control the stabilities of the resulting alpha-amino radical intermediates. Finally, the SET-sensitized reactions of these (aminoethyl)cyclohexenones that proceed via the radical cyclization mechanism are shown to display modest-to-low degrees of stereoselectivity.