Sequential two electron photooxidation of t-amines: Generation of aregiospecific iminium cation and its application in organic synthesis

Abstract

PET activation of cyclic t-amines, utilizing 9, 10-dicyanonaphthalene (DCN) as light absorbing electron acceptor in aqueous acetonitrile solution, leads to the generation of iminium cation intermediate involving electron - proton - electron (E-P-E) transfer sequence. Iminium cation generation is found to be highly regiospecific and depends upon the kinetic acidity which is subject to the stereoelectronic factor of the α -C-H proton of the unymmetrical t-amines. Tetrahydro-1, 3-oxazines (6) are synthesized in complete regio-and stereoselective manner from the PET activation of the substrates of type 4. Nucleophilic alkylation of 6 by alkyl Grignard reagents provides cis- α, α'-dialkyl cyclic amines (8). Similarly, chiral perhydropyrido[2,1-b][1, 3, 4]-oxadiazinone (11) is synthesized as a precursor for the synthesis of optically active α-alkyl piperidines. Both enantiomers of hemlock alkaloid coniine (13) are also synthesized. Furthermore, to broaden the scope of these reactions, precursor 16 is designed for the synthesis of various α -amino acids and their N-alkyl derivatives.