Singlet molecular oxygen synthesis

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

Silylenes 1 are highly reactive homologues of the carbenes, and we have been interested to compare the reactivity and primary products of the oxidation of these divalent species. In principal one can expect two different primary adducts of a silylene and molecular oxygen the formal "end-on" adducts silanone 0-oxide 2 or "side-on" adducts dioxasilirane 3 (Scheme 1). It was shown by numerous matrix studies [8-12], experiments in solution using time resolved spectroscopy [13-16], and a preparative scale synthesis in solution [17] that triplet as well as singlet carbenes yield carbonyl 0-oxides as the primary oxidation products, while dioxiranes are products of secondary photolysis. Ando et al. reported on the synthesis of the silanone 0-oxide 2e by the reaction of dimesitylsilylene le and O2 in solid argon [1]. This is so far the only experimental evidence for a silanone O-oxide. 

Having optimised the synthetic strategy for synthesis of tridachiahydropyrone (9), its conversion into the related natural product oxytridachiahydropyrone (10) was next conducted. This was achieved by irradiation of a methanolic solution of 9 in the presence of molecular oxygen and the photosensitiser methylene blue. The [4 -I- 2] cycloaddition of singlet oxygen to 9 proceeded smoothly, generating the desired product 10 in 97 % yield (Scheme 2.17). 

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