Singlet Oxygen as a Reagent in Organic Synthesis

In this chapter we review the synthesis of organic peroxides from singlet molecular oxygen [102 )] via dye-sensitized photooxygenations. The chapter comprises four 

Whilst this chapter is not comprehensive, attention is focused on those reports of photooxygenation where peroxide yields approached or exceeded 50%. The isolation of peroxides involves meticulous and potentially dangerous work [1]. Thus, percentage yields are not always reported in the same way, and may relate to the feasibility of purification and safety and, perhaps because of this issue, safety information is often incomplete. Analytical methods such as low-temperature nuclear magnetic resonance (NMR) spectroscopy has allowed the characterization of unstable peroxides in reaction mixtures. Some peroxides have been isolated in traps under vacuum or by low-temperature silica gel chromatography, while others were recrystallized at room temperature [2—4]. 

Singlet oxygen is conveniently generated by sensitization and, in view of the low energy of this species, dyes are effective and can be used in low concentrations due to the high absorptivity. 

Suitable light sources for exciting the sensitizer include halogen or mercury lamps equipped with a 400 nm cut-off filter to transmit visible light. The sensitizers methylene blue (MB), meso-tetraphenylporphine (TPP), sulfonated aluminum phtha-locyanine, and Rose Bengal (RB) are widely used in homogeneous solutions. The main appeal of heterogeneous sensitizers is that they are easy to separate from 

---