Epoxidation, basic hydrogen peroxide

Epoxidation of enones on treatment with basic hydrogen peroxide or /-butyl hydroperoxide, or with bleach, might be viewed as another form of trapping the initially produced anion.99 In this case the enol-ate, e.g. (425 Scheme 57), attacks the oxygen of the hydroperoxide to eject hydroxide and yield the epoxy ketone (426)." Finally, the initial anion can also be trapped by a sigmatropic rearrangement, as in... 

One can find quite a few cases of peroxy acids reacting for hours at elevated temperatures with simple alkenes in order to form regular epoxides. More deactivated olefins require lengthy treatment with strongly basic hydrogen peroxide solution. 

Hydration with boranes proved difficult due to extensive reductive cleavage of the epoxide (Scheme 45). The best results (54%) were achieved with borane in THF. The subsequent oxidation with basic hydrogen peroxide led to the primary alcohol as well as to saponification of the acetate. Selective protection of the primary alcohol 397 as trichloroethyl carbonate was followed by oxidation with RuCl3/NaI04, thereby producing not only the y-lactone but also the cyclic ketone. 

More recently, Grieco et at. have reported a successful epoxidation with basic /-butyl hydroperoxide in contrast to no reaction with basic hydrogen peroxide. Thus 1 can be epoxidized to 2 in 83% yield by a reaction conducted in THF at 25° for 15... 

Electron-poor double bonds can be epoxidized with basic hydrogen peroxide. See Chapter 23. 

The 1,2 dione and 1,2 diol were prepared starting from 2,4-dichlorobenzyl propyl ketone using a modification of the Mannich reaction and epoxidising the intermediate enone with basic hydrogen peroxide. Opening of the epoxide with 1,2,4-triazole followed by reduction completes the synthesis. (Figure 23). 

Another reaction where amino acids play a key role is the Julia-Golonna epoxidation of a,P-unsaturated ketones [52], which involves the use of a catalytic amount of polymeric amino acids, able to catalyze the Weitz-Scheffer epoxidation of chalcone using basic hydrogen peroxide, with high enantioselectivity (Scheme 8.17 Equation a). 

EPOXIDATION m-Chloroperbenzoic acid. Hydrogen peroxide, basic. Hydrogen peroxide—Phenylisocyanate. Hydrogen peroxide-Selenium dioxide. Iodine. Peracetic acid. Perlauric acid. Tetralin hydroperoxide. Vanadium oxyacetyl-acetonate. 

A sequence of several steps, first discussed in connection with Scheme 6.13, installs chlorine at Cg. Reaction of 23-8 with basic hydrogen peroxide starts by selective conjugate addition of peroxide anion to the distal end of the diene. That transient intermediate goes on to form the a-epoxide. Diaxial opening of the oxirane with chlorine gives chlorohydrin... 

Active epoxidizing agents can be generated in situ using basic hydrogen peroxide in combination with Af-arenesulfonylimidazoles and with phosphonic anhydrides. 

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