Bicyclic endoperoxides and synthetic applications

On the mechanism of the [4+2] cycloaddition of 1Ο2 with 1,3-dienes: Identifying the putative biradical/dipolar intermediate by employing the gem-diphenylcyclopropyl group as a mechanistic probe

“…In a final attempt to trap any involved endoperoxide intermediate, we performed the photooxygenation of dienes (E)/(Z)-1 and (Ε,Ε)/(Ζ,Ε)-2, in MeOH at 0 o C, in the presence of a mild reducing agent such as thiourea (1.1 equiv), and methylene blue (ΜΒ) as photosensitizer; endoperoxides can be reduced by thiourea to give 2-ene-1,4-diols. 15 In contrast to our initial expectations, the photooxygenation of (E)/(Z)-1 and (Ε,Ε)/(Ζ,Ε)-2 afforded (Ε)-13 and (Ε,Ε)-14, respectively, as major products (Scheme 4). 50 Control experiments in the absence of either thiourea or MB showed that both components were essential for this reaction to take place.…”

“…15 For example, the reaction of PPh 3 with endoperoxides affords stable epoxy olefins. 47,48 In the present case, the photooxygenation of…”

A New Method for the Synthesis of Stipitatic Acid Isomers: Photooxygenation of Ethyl 6H-Cyclohepta[d][1,3]dioxole-6-carboxylate

“…It is well established that thiourea reduces oxygenϪoxygen bonds to give a diol. [16] When the reduction of endoperoxide 14 with thiourea in methanol was carried out, the tropolone 16 was isolated in 57% yield as the sole product after chromatography and Scheme 2. Some transformations of endoperoxide 14: a) (H 2 N) 2 Cϭ S, MeOH, room.…”

Preparation and evaluation of a perhydroazulene intermediate for lactarane sesquiterpene synthesis

“…Lactaroruffin A (2) and several other lactarane sesquiterpenes have cis-hydroxyl groups at C-3 and C-8, and-an endoperoxide derivative of 6 seemed to be an ideal intermediate for the construction of such compounds (8). The desired endoperoxide, 13, should result from a [4+2] cycloaddition of singlet oxygen to the diene moiety of 6; however, competing ene reactions often occur at highly-substituted double bonds, and mav be a ~r o b l e m in this case.…”