Epoxidation of a,p-unsaturated ketones

9a linker = 1,4-phenylene 9b linker = 1,3-phenylene 9c linker = single bond 

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The N-anthracenylmethyl ammonium catalysts 11 and 12 also proved to be very effective in the asymmetric epoxidation of a,p-unsaturated ketones utilizing aqueous sodium165,661 or potassium1671 hypochlorite solution as an oxidant. Protection of the hydroxyl group in the N-anthracenylmethyl ammonium salts may be essential to attain high enanti-oselectivities in the epoxidation165"671, and use of... 

S. Arai, H. Tsuge, T. Shioiri, Asymmetric Epoxidation of a,p-Unsaturated Ketones under Phase-Transfer Catalyzed Conditions , Tetrahedron Lett. 1998,39,7563-7566. 

Epoxidation of a,p-unsaturated ketones using sodium perborate... 

It is worth noting that use of unprotected diarylprolinol 33 provides an effective platform for the epoxidation of a,P-unsaturated ketones [148, 149]. Within these reports it was proposed that an alternative mode of activation of the substrate could be taking place. Hydrogen bonding catalysis, rather than iminium ion formation, could explain the results and would be consistent with the non-polar reaction medium adopted within these reactions. 

In conjunction with the chiral anion TRIP (156) (10 mol%), diamine 157 (10 mol%) can be used in the catalytic asymmetric epoxidation of a,p-unsaturated ketones (>90% ee) [196], while the secondary amine 158 (10 mol%) can be used for the epoxidation of both di- and trisubstituted a,P-unsaturated aldehydes (92-98% ee) (Fig. 15) [211], The facile nature of these reactions, using commercially available peroxides as the stoichiometric oxidant, together with the synthetic utility of the epoxide products suggests application in target oriented synthesis. 

Benzylquininium chloride has shown good to excellent selectivity in the epoxidation of a,p-unsaturated ketones. Oxidation of quinone (2) in the presence of (1) with aqueous t-Butyl Hydroperoxide and Sodium Hydroxide in toluene gave rise to a 95% chemical yield of epoxide (3) in 78% ee (eq 1). Recrystallization improved the ee to 100% with 63% mass recovery. Aqueous Hydrogen Peroxide decreased both the yield (89%) and enantioselectivity (50% ee). 

Conjugated dienes can be epoxidized (1,2-addition), although the reaction is slower than for corresponding alkenes, but a,p-unsaturated ketones do not generally give epoxides when treated with peroxyacids.The epoxidation of a,p-unsaturated ketones with hydrogen peroxide under basic conditions is known as the Waits-Schejfer epoxidation, discovered in 1921. This fundamental reaction has been extended to a,()-unsaturated ketones (including quinones), aldehydes, and... 

Epoxidation of a,p-Unsaturated Ketones Using Alkaline Hydrogen Peroxide... 

C. Bassin, A. Gusso, F. Pinna, G. Strukul, Platinum-catalyzed oxidations with hydrogen peroxide The (enantioselective) epoxidation of a,p-unsaturated ketones, Organometallics 14 (1995) 1161. 

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). 

Epoxides of a,p-unsaturated ketones can undergo a ring opening/arylation reaction under Heck conditions <05JOC4720>. Epoxide 62 undergoes an initial Pd-catalyzed rearrangement to a 1,2-cyclohexanedione which then undergoes a Heck arylation reaction to... 

The use of optically resolved PTC catalysts for the synthesis of enantiomerically pure compounds is no doubt an attractive field. Asymmetric PTC has become an important tool for both laboratory syntheses and industrial productions of enantiomerically enriched compounds. Recently, Lygo and coworkers [207-216] reported a new class of Cinchona alkaloid-derived quaternary ammonium PTC catalysts, which have been applied successfully in the enantioselective synthesis of a-amino acids, bis-a-amino acids, and bis-a-amino acid esters via alkylation [207-213] and in the asymmetric epoxidation of a/p-unsaturated ketones [214-216]. 

Naturally occurring peptides can also be used to catalyze reactions other than hydrolytic. Although the present survey is not exhaustive one can note, for example, that in the epoxidation of a,P-unsaturated ketones by basic hydrogen peroxide (eq. 6) that the polypeptide (14) acts as an efficient catalyst producing enantiomeric excesses of (75) of up to 93%... 

Inexpensive sodium percarbonate can be used, both as oxidant and base [135], for the asymmetric epoxidation of a,p-unsaturated ketones using silica-grafted PLL 93 [136]. Tang and co-workers [136] have described the best results with a silica-grafted PLL with = 45. Under these conditions, the epoxidized products were obtained with 70-93% ee and 40-94% yield (Scheme 12.19). The catalyst can be recovered and reused with no erosion in the observed ee s. 

On the other hand, an enantioselective epoxidation of a,p-unsaturated ketones was developed by Zhu et al. by using easily aceessible and recoverable fluorous a,a-diaryl-L-prolinol as an organocatalyst and tert-butyl hydro-genperoxide (TBHP) as an oxidant. As shown in Scheme 7.5, the corresponding epoxides have been obtained for a number of substrates with moderate to good enantioselectivities of up to 84% ee. 

Fioroni, G., Fringuelli, F., Rizzo, F. Vaccaro, L. (2003). Epoxidation of a,P-Unsaturated Ketones in Water. An Environmentally Benign Protocol, Green Chemistry, 5, pp. 425-428... 

The Zhao group recently disclosed an enantioselective epoxidation of a,P-unsaturated ketones promoted by primary-secondary diamine catalyst 13c the corresponding epoxides were obtained with excellent enantioselectivities (Scheme 3.19) [55],... 

Scheme 1.47 Lattanzi s amine epoxidation of a,p-unsaturated ketones 1.2.2.5 Amine Catalysis...

Table 5.10 Enantioselective epoxidation of a,p-unsaturated ketones 36 with heterogenized Shibasaki s catalysts 35. ...

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