Ketones, 7,8-epoxy reduction

Conversion of a-haloketones to olefins using hydrazine (via enedlitnides C-C-N NH). Also reduction of o,3-epoxy ketones to allyl alcohols. 

Borohydrides reduce a-substituted ketones to the corresponding a-substituted alcohols, and such products can be further reduced to olefins (see section VIII). Other reagents serve, through participation of the carbonyl group, to remove the substituent while leaving the ketone intact. The zinc or chromous ion reduction of a-halo ketones is an example of this second type, which is not normally useful for double bond introduction. However, when the derivative being reduced is an a,jS-epoxy ketone, the primary product is a -hydroxy ketone which readily dehydrates to the a,jS-unsaturated ketone. Since... 

Hydriodic acid at low concentration in acetic acid will also effect the reduction of a,j5-epoxy ketones to a,jS-unsaturated ketones ... 

Wohf-Kishner reductions of a,jS-epoxy ketones give allylic alcohols, thus providing a means of reversing the arrangement in a,jS-unsaturated ketones or allylic alcohols. The reaction as first described by Wharton proceeds very readily (at room temperature in some instances) and the addition of strong base is unnecessary for example, the reduction of the epoxy ketone 143. 

Rearrangement of a,/B-epoxy ketones to ftdicarbonyl isomers, 307 Reductive alkylation, 97 Reductive cleavage of halo ethers, 264 Reductive degradation of 19-substitutional steroids, 277, 278 Reformatsky reaction, 139 Removal of the C-10 substituent in steroids. 272... 

Silanes And Base. In the presence of bases, certain silanes can selectively reduce carbonyls. Epoxy-ketones are reduced to epoxy-alcohols, for example with (MeO)3SiH and LiOMe. ° Controlling temperature and solvent leads to different ratios of syn- and anti- products.Silanes reduce ketones in the presence of BF3-OEt2 ° and transition metal compounds catalyze this reduction. ... 

This reduction of epoxy ketones has been used to prepare a number of santan-olides from the diepoxide (1) of a-santonin.2 Thus reduction of 1 is accompanied by dehydration of the intermediate tertiary alcohol to give dehydroisoerivanin (2) in 80% yield. 

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

Reduction of a, ji-epoxy ketones with NaHTe (typical procedure) ji-Epoxy ketonesP To a solution of NaHTe (prepared from Te (1.30 g, 10 mmol) and NaBH (0.90 g, 0.24 mmol)) in EtOH is added isophorone oxide (0.616 g, 4 mmol) in EtOH (4 mL). An instantaneous... 

The synthesis of the non-natural ( )-7,14-epz-l(15),8-dolastadien-7,14-ol (rac-7yl4-epi-l09) was published by Paquette in 1986 and is highlighted by a photochemical rearrangement of the 6,6,6-tricyclic a,yS-epoxy ketone 148 into the 5,7,6-tricyclic dolastane skeleton (149) (Scheme 23) [84]. The succeeding hydroxylation of carbon atom by photo oxygenation with singlet oxygen as well as a DIBAH reduction of a keto function proceeded with an undesired substrate-induced diastereoselectivity to provide the racemic 7,14-epimer of the natural dolastane 109. 

Additionally, 1,2-dihydroxyethylene dipeptide analogues without the C-terminal carboxylic acid have been used to obtain aspartyl proteases inhibitors.[641 These efforts include stereoselective alkylation of imines, one-pot reductive amination of epoxy ketones, ring opening of epoxides with sodium azide, diastereoselective dihydroxylation of allylic amines, and enzymatic resolution and stereocontrolled intramolecular amidation. 

Hydrogenation of the a -epoxy ketone shown in Eq. 365) over platinum in ethyl aoet te was found by Reese1441 to leave the epoxide ring intact. Tetrasubstituted ethylene oxides are notoriously unremaivc toward most reagents, and catalytic reduction proves to be unexceptional in this respect. 

Three a -epoxy ketones reported by Bodiuros1 188 to undergo reduction to the corresponding ccjS-unsaturated ketones on treatment with potassium iodide in. acetio acid are shown in Eqa. (407) and (403). 

The uac of OB - ion to effect reduction of various a./J-upnxA ketones to a 0-unsaturated ketones was explored by Cole and Julian 3 with several simple epoxides. Particular success has been encountered with this technique. (Eqa. 426a and 426b), however, in the sroroid field.277 A paper by Barton and co-workers also describes tliia method in connexion with the reduction of a tetrasubstituted < - epoxy ketone diterpene. ... 

Reduction of ot, -epoxy ketones chiral aldols.3 a,p-Epoxy ketones are reduced by Sml2 in THF/CH3OH at -90° to p-hydroxy ketones with retention of stereochemistry at the p-, but not at the a-position. 

Reduction of an optically active epoxy ketone gives a chiral p-hydroxy ketone (equation I). 

The method is a modification of one used by Barton and McCombie.8 Reduction of ketones.9 Ketones can be reduced to alcohols by Bu3SnH in the presence of either AIBN or a Lewis acid, but this reaction is limited to unhindered ketones. However, even sterically hindered ketones, such as f-butyl methyl ketone, can be reduced under high pressure (10 kbar) in the absence of a catalyst. This method is particularly useful in the case of cyclopropyl and a,p-epoxy ketones, which are reduced to the corresponding alcohols. Reduction of these ketones with Bu3SnH under radical conditions results in ring-opened products. 

Reduction of ttjl-epoxy ketones. These ketones arc reduced with high stereoselectivity to err/Aw-epoxy alcohols ( > 90% erythro) by Zn(Blt4), in ether, regardless... 

When dienones such as 55 are subjected to the epoxidation conditions the electron-poorer C=C double bond is selectively epoxidized. The other C=C bond can be functionalized further, for example, it can be dihydroxylated, as shown in the synthesis of the lactone 56 (Scheme 10.11) [82]. Stannyl epoxides such as 57 (Scheme 10.11, see also Table 10.8, R1 = n-Bu3Sn) can be coupled with several electrophiles [72], reduction of chalcone epoxide 58 and ring opening with alkyl aluminum compounds provides access to, e.g., the diol 59 and to phenylpropionic acids (for example 60). Tertiary epoxy alcohols such as 61 can be obtained with excellent diastereoselectivity by addition of Grignard reagents to epoxy ketones [88, 89]. 

Miyashita, M. Suzuki, T. Hoshino, M. Yoshi-koshi, A. The organoselenium-mediated reduction of a,fl-epoxy ketones, a,fl-epoxy esters, and their congeners to /J-hydroxy carbonyl compounds novel methodologies for the synthesis of aldols and their analogs. Tetrahedron 1997, 53, 12469-12486. 

Hardouin, C. Chevallier, F. Rousseau, B. Doris, E. Cp2TiCl-Mediated selective reduction of a, / -epoxy ketones./. Org. Chem. 2001, 66, 1046-1048. 

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. 

Hasegawa and colleagues recently reported the reductive ring opening of epoxy ketones 114 to 3-hydroxy ketones 116 catalyzed by 1 mol% of 110 (Fig. 29). Dihydrobenzimidazole 115 served as a reducing agent acting similarly to 112 [182]. 

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