Allylic hydroperoxide formation

Cyclic hydrocarbons, diastereoselective allylic hydroperoxide formation, 861-3, 864 Cyclic olefins, final ozonides, 718 Cyclic peroxides... 

Risk labels, lATA/ICAO, 751-3 Risk phrases, 621, 748, 749 River water, peroxide determination, 642 RNA, ozone disinfection, 616 ROS see Reactive oxygen species Rose Bengal sensitized photooxidation, 890 Rotational barriers, regioselective allylic hydroperoxide formation, 836, 847-9 Rotational isomers, peroxynitrous add, 8-9 Rotational spectra, ozonides, 721, 722-3 RP-HPLC, hydrogen peroxide determination, 627... 

A number of hindered and relatively unreactive alkenes such as adamanty-lideneadamantane (30) undergo reaction with 02(1Ag) to yield the corresponding dioxetane. This clearly reflects the fact that, for non-activated alkenes of this type, allylic hydroperoxide formation is sterically impossible. Several papers [139-142] have reported the concomitant formation of the corresponding epoxide and this has been assumed [143] to indicate the intermediacy of a perepoxide (Eq. (53)). 

Fignre 14. Potential energy curves for dioxetane and allylic hydroperoxide formation. For dashed line see text. From [198] with permission. Copyright 1985, Pergamon Press. 

The allylic hydroperoxides generated by singlet oxygen oxidation are normally reduced to the corresponding allylic alcohol. The net synthetic transformation is then formation of an allylic alcohol with transposition of the double bond. 

Alternatively the allylic hydroperoxide can undergo the so called Hock-type fragmentation621 under acid-catalyzed hydrolysis with formation of two carbonyl compounds (or moieties). The sesquiterpene (—)-geijerone has been obtained from the triene (+)-y-elemene by such a sequence (6.15) 622>. 

In 1993, Blatter and Frei [34] extended the Aronovitch and Mazur [28] photo-oxidation into zeolitic media, which resulted in several distinctive advantages as described below. Irradiation in the visible region (633 nm) of zeolite NaY loaded with 2,3-dimethyl-2-butene, 16, and oxygen resulted in formation of allylic hydroperoxide, 17, and a small amount of acetone. The reaction was followed by in situ Fourier-transform infrared (FTlR) spectroscopy and the products were identified by comparison to authentic samples. The allylic hydroperoxide was stable at - 50°C but decomposed when the zeolite sample was warmed to 20°C [35]. In order to rationalize these observations, it was suggested that absorption of light by an alkene/Oi charge-transfer complex resulted in electron transfer to give an alkene radical cation-superoxide ion pair which collapses... 

The crosslinking process is different depending on whether the unsaturation is an unconjugated double bond as in oleic acid or a conjugated double bond as in linoleic acid. Unconjugated double bonds undergo crosslinking by the initial formation of an allylic hydroperoxide... 

Selective formation of allylic hydroperoxides via singlet oxygen ene reaction... 

II. REGIOSELECTIVE FORMATION OF ALLYLIC HYDROPEROXIDES A. Site Selectivity... 

---