Ketone enones from

The fragmentation is stereospecifically anti as shown by complementary geometry obtained in the cleavage of the epimeric pair of epoxycyclobutanones 91 and 92 (Eq. 110). The fragmentation product 93 of cyclobutanone 91 is transformable into the dimethyl ester of the pheromone of the Monarch butterfly. Considering the availability of the starting epoxy ketones from enones, the oxasecoalkylation serves to reorient the oxidation pattern with chain extension as summarized in Eq. 111. 

Another preparative method for the enone 554 is the reaction of the enol acetate 553 with allyl methyl carbonate using a bimetallic catalyst of Pd and Tin methoxide[354,358]. The enone formation is competitive with the allylation reaction (see Section 2.4.1). MeCN as a solvent and a low Pd to ligand ratio favor enone formation. Two regioisomeric steroidal dienones, 558 and 559, are prepared regioselectively from the respective dienol acetates 556 and 557 formed from the steroidal a, /3-unsaturated ketone 555. Enone formation from both silyl enol ethers and enol acetates proceeds via 7r-allylpalladium enolates as common intermediates. 

Notably, some substrates possess enough steric bias to exert sterospecificity for the Bucherer-Bergs reaction. For instance, ketone 21, derived from enone 20 via a Corey-Chaykovsky reaction, underwent a Bucherer-Bergs reaction to fashion spirohydantoin 22 as a single isomer. 

Through a short sequence of functional group manipulations, compound 6 could be elaborated from allylic alcohol 7, the projected product of a Wharton fragmentation4 of epoxy ketone 8 (vide infra). In turn, compound 8 could be derived from enone 9. In the synthetic direction, a Michael addition5 of hydroperoxide anion to enone 9 would be expected to take place from the less hindered side of the molecule. Epoxy ketone 8 would fhen form upon collapse of the intermediate enolate with concomitant expulsion of hydroxide ion (see arrows, Scheme 2). 

There are many possibilities and I shall simply analyse the published synthesis. Removal of the methyl group from (50) gives ketone (51) which can be made from enone (52) by Michael addition of an ethyl group. Unambiguous cross-condensation between enolisable (54) and reactive (53) gives (52). 

In the case of 3-substituted cyclopentanones or cycloheptanones, derivatization with diamine is slower, and the reaction time ranges from a few minutes to several hours. This method is not applicable to acyclic ketones and enones. 

Judging from their reduction potentials, ET should be a feasible process between Me2CuLi and alkyl aryl ketones or enones. In order to detect the occurrence of ET, House... 

Lithium-ammonia reduction of a,/ -unsaturated ketones (entry 6, Scheme 1.4) provides a very useful method for generating specific enolates.26 The desired starting materials are often readily available, and the position of the double bond in the enone determines the structure of the resulting enolate. This and other reductive methods for generating enolates from enones will be discussed more frilly in Chapter 5. Another very important method for specific enolate generation, the addition of organometallic reagents to enones, will be discussed in Chapter 8. 

Mixed homocuprates.7 Mixed cuprates (1) in which the nontransferable ligand is an a-sulfonyl carbanion are easily prepared from dimethyl sulfone or methyl phenyl sulfone (equation I), and are effective for conjugate addition to enones and for a synthesis of ketones from acid chlorides. 

Why does the stabilized ylid prefer to react with the double bond In order to understand this, let s consider first the reaction of a simple, unstabilized ylid with an unsaturated ketone. The enone 1 has two electrophilic sites, but from Chapters 10 and 23, in which we discussed the regioselectivity of j attack of nucleophiles on Michael acceptors like this, you would expect that direct 1,2-attack on the i ketone is the faster reaction. This step is irreversible, and subsequent displacement of the sulfide i leaving group by the alkoxide produces an epoxide. It s unimportant whether a cyclopropane prod- uct would have been more stable ihe epoxide forms faster and is therefore the kinetic product. 

The reagent forms the expected adducts with aldehydes and ketones in high yield. It can be used for preparation of t-butoxymethyl ketones from acid chlorides (equation 1). In combination with CuBr, it undergoes conjugate addition to a,p-enones (equation II). 

The oxidation of ketones to enones via the reaction of their silyl enol ethers with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) has been suggested originally to proceed via allylic hydride abstraction [195-198]. A recent reinvestigation, however, [199] has established the intermediate formation of a substrate-quinone adduct 96 which was presumably formed from a geminate radical ion pair after electron transfer. Decomposition of the adduct then finally afforded the observed enone product 97. Recently, the critical role of solvent polarity in the formation of 97 from the PET reaction of 93 and chloranil has been identified by time-resolved spectroscopy [200]. 

Ylides derived from the salts obtained by A. A -dialkylation of sulfoximines and anions derived from A -tosylsulfoximines are useful reagents for the synthesis of epoxides or cyclopropanes from aldehydes and ketones or enones. ... 

Cyclization of Divinyl Ketones from p(-Substituted Enones... 

Cyclization Divinyl Ketones from of-Hydroxy Enones... 

The formation of epoxy ketones from sterically crowded enones is often difficult. Avoiding the epoxi-dation step, fragmentation to give the alkynone (137 Scheme 47) occurs on treatment of the unsaturated hydrazones (145) (from 135) with an excess of NBS in methanol. Ohloff and Buchi used this sequence for a further synAesis of exaJtone (118) and muscone (119). 

Conjugate additions. p-Silyl ketones are formed from enones by their reaction with disilanes in the presence of Cu(OTf)j and BUjP. The ethyl transfer from EtjZn is accelerated by catalytic amounts of Cu(OTf)2 and/or triethyl phosphite. ... 

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