A,0-epoxy ketones

The a, /3-epoxy ketone 119 and esters are hydrogenolyzed with triethylam-monium formate or H2 chemoselectively to aldols[116]. 

The opening of a, (3-epoxy ketones, as recently reported by Doris et al., can also be carried out with catalytic amounts of titanocene dichloride [16]. Thus, the relatively sensitive (3-hydroxy ketones are also readily tolerated under the catalytic conditions. 

Both enantiomers of a, (3-epoxy ketones can be synthesized essentially at the same cost since both (R)- and (5)-BINOLs are sold at almost the same price. 

The cyclic a-chloro ketone 81 which forms the (Z)-enolate only also underwent the asymmetric Darzens condensation with various aldehydes by use of the Merck catalyst 7 (R=4-CF3, X=Br) under analogous conditions to furnish the a,(3-epoxy ketones 82 with up to 86 % ee,160611 as shown in Scheme 25. It should be noted that this high enantioselectivity was attained by the reaction at room temperature. 

Reduction of a,(3-epoxy ketones by hydrazine to allylic alcohols. 

On addition of S04 to the triple bond in the lO-member cycloalkyne 24 and cyclo-aUcynone 27, a nonchain, and anionic, self-terminating radical cyclization cascade is induced. In the former reaction (equation 22) the bicyclic ketones 25 and 26 are formed, and in the latter reaction (equation 23) the a,/3-epoxy ketones 28 and 29 are formed in good yields. Because of the difficulty of oxidizing isolated triple bonds, 804 does not react as an electron-transfer reagent in these reactions but acts as a donor of atomic oxygen. 

For other methods of fragmentation of a,3-epoxy ketone derivatives, sec Mac Alpine Warkcntin Can. J. Chem. 1978, 56. 308, and references cited therein. 

The opening of epoxides with neighboring keto groups, accompanied by vinylogous / -elimination, has already been mentioned (section V). This is an extension of the -elimination reactions which occur when a,(3- or j8,y-epoxy ketones are opened with acid or base. a,/3-Epoxy ketones give a-substituted a,j8-unsaturated ketones [(162), for example], and j8,y-epoxy ketones give -substituted a,/3-unsaturated ketones [(163), for example] ... 

A stereospecific and stereoselective synthesis of 2-(l-hydroxyalkyl)-l-alkylcyclo-propanols (46) has been realized from a,/3-epoxy ketones and bis(iodozincio)methane (Scheme 22).127 The diastereoselective reaction has been explained by chelation (g) effects. 

Reduction.1 a, 3-Epoxy ketones are selectively reduced to (3-hydroxy ketones, even when the substrate (2) also contains an enone group. Reduction of 2 with Zn/Cu also results in the same product (3), but in low yield as well as a number of products including the fully saturated ketone 4. 

Cleavage of a,[i-epoxy ketones.1 The reagent (1), possibly (CH3)2SC1, formed from DMSO and ClSi(CH3)3, cleaves a,(3-epoxy ketones to 2-chloro-3-hydroxy ketones with high regioselectivity (equation I). If the epoxide has a phenyl substituent, 3-chloro-2-hydroxy ketones are formed (equation II). 

The reduction of a, (3-epoxy ketones using Sml2 is also possible. A range of acyclic and cyclic epoxides with different substitution patterns underwent reduction to give the desired aldol products in good yields (Scheme 4.26).31... 

These reactions become more realistic if derivatives of a,/3-epoxy ketones are used. These can be easily prepared by oxidation of the corresponding a,/3-unsa-turated ketones with peracids or hydrogen peroxide (Scheme VIII/13). The driving force in studying this kind of reactions is the importance of the economic synthesis of the natural 15-membered ketones, muscone and cyclopentadeca-none, from cyclododecanone, an easy available and inexpensive starting material (Scheme VIII/14) [35] [36]. 

Pyrolysis, photolysis, and electronolysis of ethylene oxide (128) yielded similar products (P. Brown et al., 1966). Electron impact-induced fragmentation (129) of the epoxide (51) (P. Brown et al., 1966) was similar to the photochemical behaviour (130) of the epoxide (52) (Kristinsson and Griffin, 1966). Rearrangement of the a,/3-epoxy-ketone to the diketone after ionization (131) has been suggested to account for... 

Mai and co-workers have reported that the deoxygenation of cyclic a,/3-epoxy ketones (and acyclic a,/3-epoxy esters) is accomplished in high yields under mild and neutral conditions by the use of Mo(CO)6 (Table 14) <2003TL2355>. 

Other halogenated compounds have been substituted for the halo esters. Aromatic a-halo ketones have been condensed with aromatic aldehydes to give a,/3-epoxy ketones. ... 

Under irradiation conditions, imidazolines are excellent hydrogen donors. For example l,3-dimethyl-2-phenylben-zyimidazoline 639 reduces a,(3-epoxy ketones in the presence of proton donors (Scheme 152) <2001S1248>). 

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