Ketones, a-mercurio

Next to the cyclopropane formation, elimination represents the simplest type of a carbon-carbon bond formation in the homoenolates. Transition metal homoenolates readily eliminate a metal hydride unit to give a,p-unsaturated carbonyl compounds. Treatment of a mercurio ketone with palladium (II) chloride results in the formation of the enone presumably via a 3-palladio ketone (Eq. (24), Table 3) [8], The reaction can be carried out with catalytic amounts of palladium (II) by using CuCl2 as an oxidant. Isomerization of the initial exomethylene derivative to the more stable endo-olefin can efficiently be retarded by addition of triethylamine to the reaction mixture. 

Condensation of aldehydes with a-mereurio ketones. In the presence of BF3 elhcrate, a-mercurio ketones condense with aldehydes with moderate to high erylhro-sclection. 

In contrast to intermolecular photoaldols, which can be manipulated with facility, intramolecular cycloadducts undergo retro-[2 + 2] cycloaddition when subjected to hydrolytic conditions. In an alternative protocol, oxymercuration of (229) afforded a-mercurio ketone (230 42%) which was acetylated under standard conditions to provide 1,4-diketone (231) quantitatively. Similarly, epoxidation of (229) provided functionalized photoaldol (232), which was hydrolyzed and acetylated to form a-acetoxy derivative (233). Finally, hydrolysis of (234) (4 1 THF/0.1 N HCl) gave lactol (235) in nearly quantitative yield, illustrating the utility of the intramolecular furan carbonyl photocycloaddition in spirocycle formation. 

Table 8 SynxAnti Selectivity in the BFs OEtj-catalyzed Aldol Reactions of a-Mercurio Ketones with Aldehydes...

Palladium homoenolates readily undergo p-elimination to give a,P-unsaturated carbonyl compounds. Treatment of a mercurio ketone with a catalytic amount of palladium(II) in the presence of CuCh results in the formation of an enone via a 3-palladio ketone (Scheme 3). Treatment of a silyloxycyclopropane (8) with PdCh also generates in situ a palladium homoenolate which then undergoes -elimination (Scheme 3). Heating a mixture of a 3-trichlorostannyl ketone or aldehyde with DMSO results in the formation of an enone or an enal in excellent yield (Scheme 4). ... 

The reaction of a mercurio ketone with NaBRt produces a radical species which can be trapped in situ by a reactive acceptor such as a vinyl ketone. - Treatment of a mixture of a mercurio ketone and an electron-deficient terminal alkene (or fumarate) in CH2Q2 with concentrated aqueous NaBH4 gives a conjugate adduct (Scheme 19). Isomerization of such a homoenolate radical, presumably via an intermediate cyclopropanoxy radical, has been observed in the reaction of a mercurio aldehyde (Scheme 20).37.38 direction of the isomerization is opposite to that observed in the reactions of anionic ho-moenolates. Such a rearrangement has been used for a ring expansion reaction. ... 

The reaction of a mercurio ketone and carbon monoxide in the presence of a palladium catalyst in methanol (Scheme 26) results in the formation of a 1,4-keto ester with incorporation of one molecule of carbon monoxide. Treatment of a mercurio ketone with [Ni(CO)4] results in symmetrical coupling with incorporation of one molecule of carbon monoxide to give a triketone, presumably via a 3-nickel-sub-stitut ketone (Scheme 27) Such symmetrical coupling reactions are general for alkylmercury compounds. If silyloxycyclopropane (8) is heated in CHCb in the presence of a catalytic amount of a palladium-phosphine complex under CO, symmetrical coupling with incorporation of one molecule of CO takes place to give a 4-ketopimelate (Scheme 27). ... 

Enol stannanes of cyclohexanone and propiophenone have been indicated to take part in r/treo-selective aldol reactions with benzaldehyde at low temperatures e.g. —78 °C), but to be erythro-seAsciiwe at higher temperatures ca 45 °C). Two complementary methods have been described for stereoselection in aldol-type reactions. Whilst a-mercurio-ketones show eryr/wo-selection in their reactions with aldehydes in the presence of boron trifluoride diethyl etherate, pre-formed lithium enolates and aldehydes, in the presence of simple trialkyl-boranes, lead to mixtures that are rich in the more stable threo-d do product. Aldol-type products arise from 1,3-alkyl migrations of alk-l-enyl alkyl acetals and ketals, in a reaction that is catalysed by boron trifluoride diethyl etherate (Scheme 52). Diastereoselection is possible, since (.E)-alkenyl acetals give the... 

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