A,/3-ethylene ketones

Owing to their particular interest two individual reactions will now be discussed separately. The reaction of methoxycarbonylhydrazine and 3-bromo-2,4-pentanedione affords, in addition to the expected pyrazole (608), a pyrazolium salt (609), the structure of which was established by X-ray crystallography (74TL1987). Aryldiazonium salts have been used instead of arylhydrazines in the synthesis of pyrazolines (610) and pyrazoles (611) (82JOC81). These compounds are formed by free radical decomposition of diazonium salts by titanium(n) chloride in the presence of a,/3-ethylenic ketones. 

The reaction of 1,4-bis-zinc derivatives with CuCN-2LiCl allows the preparation of a range of new polyfunctional zinc-copper reagents.309 They undergo selectively 1,4-additions on a,/3-ethylenic ketones in the presence of TMSC1 providing a new zinc-copper reagent, which can react with another electrophile (Equation (175)). 

Condensation of a-/3 ethylenic ketone enolates. We started this work79 independently and simultaneously with Sammes and Wallace80 on ketones enolisable on the side, relative to the ketonic group, where the insaturation is. In those cases, use of complex base NaNH2-f-BuONa is needed. Mechanisms are rather complicated as may be seen in Scheme 44 where we have collected our own results79 and those of Sammes and Wallace81. ... 

Reaction with afi-unsaturated ketones. 1-Siloxy-l-vinylcyclopropanes can be prepared easily by cyclopropanation of cisoid or labile a,/3-ethylenic ketones. It has already been shown that 1-vinylcyclopropanols undergo ring expansion to cyclobutanones on treatment with acid and to cyclopentanones on thermolysis. Two examples of this useful new cyclopropanation sequence are shown in... 

In the absence of activation, the carbonyl group (aliphatic ketones and aldehydes) is too weak an electrophore to exhibit a specific reduction in aqueous media. Moreover, aldehydes may lead to hydrates, the reduction of which is even more difficult. On the contrary, activation by a double bond(s) or an aromatic ring in the a position allows one to reduce carbonyl groups. Thus, in acidic media one observes a one-electron step (reduction of the protonated form of carbonyl) that affords the formation of dimers a mixture of pinacols with aromatic ketones or coupling in -diketones with a,/3-ethylenic ketones. 

HS(CH2) SH, BF3-Et20, CH2CI2, 25°, 12 h, high yield, n = 2, n = 3. In a,/3-unsaturated ketones the olefin does not isomerize to the /3,7-position as occurs when an ethylene ketal is prepared. Aldehydes are selectively protected in the presence of ketones except when steric factors force the ketone to be protected as in the example below." A TBDMS group is not stable to these conditions. ... 

Ethylenimines may also be prepared by the reaction of 1,2-dihaloalkanes with amines or ammonia. For example, ethylenimine may be prepared in the laboratory or on an industrial scale by the reaction of ethylene dichloride with ammonia [42]. The reaction of amines with a,/3-dibromo ketones yields imines as described in Eq. (18) [43]. 

One of the features of a,/3-unsaturated ketones is the presence of two electrophilic centers. Because of this feature, reactions with binucleophiles can proceed as a 1,2-addition or as a 1,4-addition. Regarding three-membered nitrogen-containing heterocycles formed from a,/3-unsaturated ketones and their derivatives, the unsaturated ketone acts either as a 1,2-bielectrophile (substituted ethylene), which leads to the formation of ethyleneimines, or as a 1,4-bielectrophile, giving rise to either bi- or tricyclic aziridines. Hence, the present chapter is divided into two parts, one which is entirely dedicated to aziridinyl ketones and the other to bi- and tricyclic aziridines. 

Some assumptions about a sequence of reactions of unsaturated ketones and cyanoacetic acid derivatives can be drawn from the results of [146], which described several reaction products 134-140 and their isolation (Scheme 3.43). In the same publication it was also established that the presence of an excess of a, 3-unsaturated ketone 24 in the reaction mixture led to the addition of the initially formed tetrahydropyridine to the ethylene bond of the enone system. 

When an oxidative coupling or addition takes place in the presence of carbon monoxide, CO insertion occurs leading to ketones. The Ru3(CO)12-catalyzed reaction of alkenylpyridyl or Af-(2-pyridyl)enamines and ethene performed under an atmosphere of carbon monoxide leads to the selective formation of a,/3-unsaturated ketones [16] (Eq. 11). After activation of the vinyl C-H bond, insertion of both carbon monoxide and ethylene takes place to give 25. 

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... 

Selective enone ketalization. The reaction of ethylene glycol catalyzed by pyri-dinium p-toluenesulfonate (PPTS) does not discriminate between saturated and a, 3-unsaturated ketones. In contrast, this hindered pyridinium salt (1) permits selective ketalization of enones in the presence of saturated keto groups. 2,6-Lutidinium p-toluenesulfonate (2) is as effective. 

On the other hand, 1,4-addition of saturated, vinylic and phenylic Grignard reagents may be catalyzed by Cu salts [for examples, see Refs. 1-4,10,11]. When the a,j -ethylenic ketones possess a j -electron-donor group (e.g., an ether or amine group), the reaction proceeds through a 1,4-addition-elimination process [3 Eq. (3)] ... 

When we draw a similar resonance structure for an ,/3-unsaturated carbonyl compound, however, the positive charge is allylic and can be shared by the jS carbon. In other words, the /3 carbon of an ,j8-unsaturated carbonyl compound is an electrophilic site and can react with nucleophiles. A comparison of electrostatic potential maps of ethylene with an a,/3-unsaturated ketone shows that the double-bond carbon atoms of the unsaturated ketone are more positive (more green) than those of the isolated alkene ethylene. 

Sodium and potassium borohydrides are above all used for reducing aldehydes and ketones (Sections 3.2.1, 3.2.2) a,p-ethylenic ketones are converted to mixtures [W3]. In alcoholic media or THF, they leave epoxides, esters and lactones, acids, amides, and most nitro compounds unreacted, but they reduce halides (Section 2.1), anhydrides (Section 3.2.6), quartemary pyridinium salts (Section 3.3), double bonds conjugated to two electron-withdrawing groups (Sections 3.2.9, 4.4), and CUPd... 

In general, synthesis of 4-isoxazolines is accomplished via three routes 1,3-dipolar cycloaddition of nitrones to alkynes or by the oximation of a,i -ethylenic ketones, a-alkynic ketones and aldehydes or from the selective reduction of isoxazolium salts. The nitrone (262) underwent tandem cyclo-addition-[2,3]sigmatropic rearrangement with allenyl sulfoxide (263). And it resulted in 4-isoxazoline (264) (Equation (46)) <89TL663>. 

COPPER-CATALYZED CONJUGATE ADDITION OF ORGANOMANGANESE CHLORIDES,3 RMnCI, to a.p-ETHYLENIC KETONES IN THF AT 0°C... 

Addition of Germylenes to Multiple Bonds. Addition reactions of germylenes to the C=0 of para quinones typically yield alternating 2 1 polymers. An exception was noted for Ge[N(SiMe3)2)2 which gave a 1 1 polymer upon reaction with 1,4-quinones. Cyclic a, /3-unsaturated ketones and ethylene and propylene sulfide have also been found to be excellent monomers for the formation of alternating copolymers. Recall that related reactions with quinones and phenones noted in the Ge-C bond formation Section (3.1.7) lead to the dearomatization of the ring and the isolation of molecular products. For 1,4-napthoquinone, both molecular and polymeric products have been observed (equation 8). 

Oxidation may then be assumed (71) to give the keto acid, in which the ethylenic linkage is conjugated with the carbonyl group this placing of the ethylenic linkage is purely speculative and not fully corroborated by the ultraviolet absorption spectrum (which, instead of the high-intensity maximum near 2350 a. expected for an isocyclic a,/3-unsaturated ketone. 

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