Singlet tandem reactions

The reactions in this section proceed through stepwise tandem additions of singlet oxygen. The overoxidation of unsaturated hydrocarbons 15 (in Freon-11 oracetone-d6),... 

Patil, S.N., Stephens, B.E. and Liu, F. (2008) A tandem Baylis-Hillman-singlet oxygen oxidation reaction for facile synthesis of "/-substituted y-hydroxy-butenolides. Tetrahedron, 64 (48), 10831-10836. 

Considerable information is available on electronic states of NO and 2 and their lifetimes. Because tandem experiments have an intrinsic time delay of tens of microseconds between ion formation and reaction, excited singlet states will undergo radiative decay to the ground state, either directly or via cascade processes, before the reactant ions reach the... 

Irradiation of cyclohexenone 32 with the tertiary a-silylamine EtjNCHjSiMej in methanol solution in the presence of the electron acceptor 9,10-dicyanoanthracene (DCA) yields predominantly the desi-lylated adduct 32b. The product ratios depend on amine concentration. " The mechanism proposed for adduct formation is outlined in Scheme 24. Oxidation of the tertiary amine by singlet DCA yields the amine cation radical, which undergoes desilylation upon nucleophilic reaction with the solvent. Addition of the a-aminoalkyl radical to the neutral enone affords the radical adduct, which is reduced by DCA and protonated by solvent. " Intramolecular trapping of the radical adduct can compete with reduction by DCA"-, as seen in the reaction of 32 with an a-silylanihne, which yields the tandem addition product 32c (Scheme 24). ... 

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