Rapid Photoracemization of Chiral Alkyl Aryl Sulfoxides

The photoracemization of chiral alkyl aryl sulfoxides with a photosensitizer has not been sufficiently investigated thus far. Therefore, in this study, a rapid photoracemization reaction of enantiopure alkyl aryl sulfoxides using 1 mol % 2,4,6-triphenylpyrylium tetrafluoroborate (TPT+) was developed. Various substitution patterns were tolerated and every racemization reaction proceeded extremely fast (k(2) = 1.77 x 10(4)-6.08 x 10(1) M-1 s(-1), t(1/2) = 0.4-114 s). Some chiral sulfoxides with easily oxidizable functional groups are not appropriate for this photo-isomerization. The electrochemical potentials of the functional groups, determined via cyclic voltammetry, are useful for predicting the reactive or nonreactive groups in this photoracemization reaction. A theoretical study was conducted to clarify the sp(2)-like nature of S of the sulfoxide cation radical, which makes photoracemization easier.