Photooxygenation allylic hydroperoxide formation

IV. SELECTIVE FORMATION OF ALLYLIC HYDROPEROXIDES BY DYE-SENSITIZED INTRAZEOLITE PHOTOOXYGENATION... 

Selective formation of allylic hydroperoxides via singlet oxygen ene reaction 837 TABLE 2. Syn/anti regioselectivity in the photooxygenation of allylic alcohols 10-2s and 10-Z... 

Possible side-reactions, such as the formation of allyl hydroperoxides from compounds having an allylic hydrogen (a competitive ene reaction Section 6.7.3) or 1,4-endoperoxides from 1,3-dienes, may be suppressed by changing the experimental conditions.1359,1438 For example, the extent of [2 + 2] and [4 + 2] photooxygenation in styrenes, such as the propenylanisole 522 (Scheme 6.253), is controlled by solvent polarity and pH, possibly due to protonation of a perepoxide/zwitterion intermediate.1421,1439 The [4 + 2] product 523 is preferentially produced in non-polar benzene or chloroform, whereas the 1,2-dioxetane 524 is almost exclusively formed in methanol or acidified non-polar solvents. 

The photooxygenation of y- and 6-pyronenes produces the expected hydroperoxides and endoperoxides (Scheme 10), further reaction of which (thermolysis, acid and base heterolysis, etc.) leads to the formation of materials with potential as perfumery or therapeutic agents. An endoperoxide hemiacetal and two allylic hydroperoxides were obtained from the methylene blue sensitized photo-oxidation of racemic phythol (Scheme 11). °... 

Geijerone (237), which was found in the fruit oil of Juniperus communis L., is probably a metabolite of an elemene 643). The biogenetic formation of (—)-geijerone (237) can be simulated by dye-sensitized photooxygenation of (-h)-Y-elemene and subsequent fragmentation of the corresponding allyl hydroperoxides 460). Nor-compounds (240) 663) and (241) 664) as well as the two C-12 derivatives (242) and (243) 363) were isolated from vetiver oil which is an important perfumery material. 

The photooxygenation of a,(i-unsaturated esters 15 with a stereogenic center at the y-position leads to allylic hydroperoxides with > 99% regiocontrol ( gem effect operates) and the preferred formation of... 

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