Chiral N-alkyl-2,4,6-triphenylpyridiniums as enantioselective triplet photosensitizers. laser flash photolysis and preparative studies.
Three N-alkylpyridinium photosensitizers having chiral alkyl groups have been prepared by reacting 2,4,6-triphenylpyrylium tetrafluoroborate ion with (1R,2S)-(-)-norephedrine, (S)-(+)-2-(aminomethyl)pyrrolidine, and (R)-(-)-1-cyclohexylethylamine. Laser flash photolysis allows detection of the corresponding triplet excited states that are quenched by hydrogen atom donors and electron donors. Asymmetric quenching of the chiral triplet excited state was observed using enantiomerically pure 1,2-diamino cyclohexane as quencher. Low enantiomeric excess values (up to 7%) were measured for the photochemical cyclization of 5-methyl-4-hexenoic acid to its corresponding gamma-lactone using these chiral N-alkylpyridinium as photosensitizers.
Alvaro
Mercedes
M
Instituto de Tecnología Química UPV-CSIC and Departamento de Química, Av. Los Naranjos s/n, 46022 Valencia, Spain.
Formentín
Pilar
P
García
Hermenegildo
H
Palomares
Emilio
E
Sabater
María J
MJ