Regioselectivity allylic hydroperoxide formation

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... 

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

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... 

E. Regioselectivity with Twisted 1,3-Dienes Allylic versus Allene Hydroperoxide Formation... 

Stratakis, M. and Orfanopoulos, M. (1993) Regioselective formation of cyclic and allylic hydroperoxides. Synthetic Communications, 23 (4), 425-430. 

In contrast to oxidation in water, it has been found that 1-alkenes are directly oxidized with molecular oxygen in anhydrous, aprotic solvents, when a catalyst system of PdCl2(MeCN)2 and CuCl is used together with HMPA. In the absence of HMPA, no reaction takes place(100]. In the oxidation of 1-decene, the Oj uptake correlates with the amount of 2-decanone formed, and up to 0.5 mol of O2 is consumed for the production of 1 mol of the ketone. This result shows that both O atoms of molecular oxygen are incorporated into the product, and a bimetallic Pd(II) hydroperoxide coupled with a Cu salt is involved in oxidation of this type, and that the well known redox catalysis of PdXi and CuX is not always operalive[10 ]. The oxidation under anhydrous conditions is unique in terms of the regioselective formation of aldehyde 59 from X-allyl-A -methylbenzamide (58), whereas the use of aqueous DME results in the predominant formation of the methyl ketone 60. Similar results are obtained with allylic acetates and allylic carbonates[102]. The complete reversal of the regioselectivity in PdCli-catalyzed oxidation of alkenes is remarkable. 

Regioselective [4-1-2] cycloadditions to Cjq are also possible with 2,3-dimethyl-buta-1,3-diene (4) and with the monoterpene 7-methyl-3-methylideneocta-l,6-diene (5, myrcene) [22]. These monoadduct formations proceed under mild and controlled conditions. Most of these addition products of 1,3-butadiene derivatives (e.g. 4, 5, 8-12) are unstable against air and light [25]. The dihydrofuUerene moiety in the Diels-Alder adducts act as a 02-sensitizer and promotes the oxidation of the cyclohexene moiety to the hydroperoxide. Reduction of the hydroperoxide with PPhj yields the corresponding allylic alcohols [25]. 

In 1996, Li and Ramamurthy reported the use of zeoHtes to enhance the regioselectivity in the O2 ene-reaction. In contrast to the reaction in solution, in which the cis effect applies, a remarkable twin selectivity is observed in zeolites. This was mechanistically rationalized in terms of coordination of the double bond to the Na+ ion in the zeoHte (cation-ti interaction), which polarizes the double bond for Markovnikov selectivity and induces conformational constraint in the allylic cis substituents (Figure 8.8). The latter effect disfavors stericaUy the formation of the cis perepoxide-like structure or prevents a perpendicular orientation of the ds-hydrogens for coordination and abstraction. Complications may arise from the formation of tertiary hydroperoxides from /one-hydrogen abstraction, which may selectively decompose on prolonged irradiation this falsifies the regioselectivity. ... 

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