Ketones, methyl vinyl hydrogenation

CH2 CH C CH. Colourless gas with a sweet odour b.p. 5°C. Manufactured by the controlled low-temperature telomerization of ethyne in the presence of an aqueous solution of CuCI and NH Cl. Reduced by hydrogen to butadiene and, finally, butane. Reacts with water in the presence of HgSO to give methyl vinyl ketone. Forms salts. Forms 2-chloro-butadiene (chloroprene) with hydrochloric acid and certain metallic chlorides. 

A more eflicient and general synthetic procedure is the Masamune reaction of aldehydes with boron enolates of chiral a-silyloxy ketones. A double asymmetric induction generates two new chiral centres with enantioselectivities > 99%. It is again explained by a chair-like six-centre transition state. The repulsive interactions of the bulky cyclohexyl group with the vinylic hydrogen and the boron ligands dictate the approach of the enolate to the aldehyde (S. Masamune, 1981 A). The fi-hydroxy-x-methyl ketones obtained are pure threo products (threo = threose- or threonine-like Fischer formula also termed syn" = planar zig-zag chain with substituents on one side), and the reaction has successfully been applied to macrolide syntheses (S. Masamune, 1981 B). Optically pure threo (= syn") 8-hydroxy-a-methyl carboxylic acids are obtained by desilylation and periodate oxidation (S. Masamune, 1981 A). Chiral 0-((S)-trans-2,5-dimethyl-l-borolanyl) ketene thioketals giving pure erythro (= anti ) diastereomers have also been developed by S. Masamune (1986). 

Cyclic g-haloacetals and -ketals have been prepared by variations on two basic methods. The most frequently used method involves the combination of an a,B-unsaturated carbonyl compound (acrolein, methyl vinyl ketone, croton-aldehyde, etc.) a diol, and the anhydrous hydrogen halide. All possible sequences of combining these three have been used. In most cases the... 

Aryl radicals are produced in the decomposition of alkylazobenzenes and diazonium salts, and by f)-scission of aroyloxy radicals (Scheme 3.73). Aryl radicals have been reported to react by aromatic subsitution (e.g. of Sh) or abstract hydrogen (e.g. from MMA10) in competition with adding to a monomer double bond. However, these processes typically account for <1% of the total. The degree of specificity for tail vs head addition is also very high. Significant head addition has been observed only where tail addition is retarded by sleric factors e.g. methyl crotonate10 and -substituted methyl vinyl ketones 79, 84). 

The reaction of crotonaldehyde and methyl vinyl ketone with thiophenol in the presence of anhydrous hydrogen chloride effects conjugate addition of thiophenol as well as acetal formation. The resulting j3-phenylthio thioacetals are converted to 1-phenylthio-and 2-phenylthio-1,3-butadiene, respectively, upon reaction with 2 equivalents of copper(I) trifluoromethanesulfonate (Table I). The copper(I)-induced heterolysis of carbon-sulfur bonds has also been used to effect pinacol-type rearrangements of bis(phenyl-thio)methyl carbinols. Thus the addition of bis(phenyl-thio)methyllithium to ketones and aldehydes followed by copper(I)-induced rearrangement results in a one-carbon ring expansion or chain-insertion transformation which gives a-phenylthio ketones. Monothioketals of 1,4-diketones are cyclized to 2,5-disubstituted furans by the action of copper(I) trifluoromethanesulfonate. ... 

An ab initio MO calculation by Jorgensen revealed enhanced hydrogen bonding of a water molecule to the transition states for the Diels-Alder reactions of cyclopentadiene with methyl vinyl ketone and acrylonitrile, which indicates that the observed rate accelerations for Diels-Alder reactions in aqueous solution arise from the hydrogenbonding effect in addition to a relatively constant hydrophobic term.7,76 Ab initio calculation using a self-consistent reaction field continuum model shows that electronic and nuclear polarization effects in solution are crucial to explain the stereoselectivity of nonsymmetrical... 

The catalytic system employing (2 - Fur)3P as ligand was applied to the coupling of methyl vinyl ketone and ethyl vinyl ketone to aromatic, aliphatic, acetylenic, and olefinic aldehydes (Scheme 23) [37]. Despite the hydrogenation conditions, alkyne and alkene moieties, as well as benzylic ether and nitro functional groups all remained intact. Furthermore, extremely high lev-... 

FIGURE 2.27 Two possible mechanisms to explain deuterium distributions resulting from deuteriumation and exchange of methyl vinyl ketone. Deuterium is assumed to move subsurface and to attack adsorbed carbons from threefold hollows. Path A multiple exchange by repeated addition-rotation-abstraction at the [3-carbon (classic mechanism) path B I -A hydrogen shift followed by desorption as enol. 

Trost et alJ2 also explored the compatibility of di-, tri-, and tetrasubstituted allenes with their intermolecular Alder-ene protocol. Multiple substituents present the opportunity for a mixture of products to arise from differing regio- and chemoselectivity. 1,1-Disubstituted allenes were coupled to methyl vinyl ketone with excellent chemo-selectivity only when one set of /3-hydrogens was activated by an cy-ester or amide (Equation (69)). If the /3-hydrogens were of similar acidity, a mixture of products was obtained, as in the coupling of allenol 103 with methyl vinyl ketone dienes 104 and 105 are produced in a 1.3 1 mixture (Equation (70)). 

Stoichiometric ionic hydrogenation of the C=C bond of a,/ -unsaturated ketones by HOTf and [Cp(CO)3WH] results in the formation of -ketone complexes of tungsten [32]. As exemplified in Eq. (17), hydrogenation of methyl vinyl ketone gives a 2-butanone complex of tungsten. The bound ketone is displaced by the triflate counterion, giving the free ketone. Similar reactions were reported for hydrogenation of the C=C bond of a,/ -unsaturated aldehydes. 

In the case of methyl vinyl ketone (MVK), similar reactivity is observed. Exposure of MVK (150 mol%) and p-nitrobenzaldehyde to basic hydrogenation conditions provides the corresponding aldol product in good yield, though poor dia-stereoselectivity is observed [24a]. Remarkably, upon use of tris(2-furyl)phos-phine as ligand and Li2C03 as basic additive, the same aldol product is formed with high levels of syn-selectivity [24 e]. Addition of MVK to activated ketones such as l-(3-bromophenyl)propane-l,2-dione is accomplished under similar con-... 

Scheme 22.8 Use of methyl vinyl ketone (MVK) in intermolecular hydrogen-mediated reductive aldol coupling.a)...

Only Cram (36) has published a rationale for the very high (99%) enantiomeric excess achieved in the reaction of methyl vinyl ketone and the hydrindanone in the presence of the chiral crown ether. This mechanism envisions a bimolecular complex comprising the potassium cation and chiral host as one entity and the enolate anion of the hydrindanone as the counterion. Methyl vinyl ketone lies outside this complex. The quinine-catalyzed reaction appears to have a termo-lecular character, since the hydroxyl of the alkaloid probably hydrogen bonds with the methyl vinyl ketone—enhancing its acceptor properties—while the quin-uclidine nitrogen functions as the base forming the hydrindanone—alkaloid ion pair. 

Kelly and colleagues91 explored the use of bisphenylenediol 103 as a catalyst in Diels-Alder reactions of a,/i-unsaturated carbonyl compounds. Activation of the dieno-phile occurred through double hydrogen bonding of the two hydroxyl functions on 103 to the carbonyl group on the dienophile. The reaction of cyclopentadiene with methyl vinyl ketone (equation 31) at ambient temperature showed, after a reaction time of 10 minutes, 3% of product formation in the absence of 103 against 90% of product formation in the presence of 0.4 equivalents of 103. 

Polymerizations of vinyl ketones such as methyl vinyl ketone are also complicated by nucleophilic attack of the initiator and propagating carbanion at the carbonyl group although few details have been established [Dotcheva and Tsvetanov, 1985 Hrdlovic et al., 1979 Nasrallah and Baylouzian, 1977]. Nucleophilic attack in these polymers results in addition, while that at the ester carbonyl of acrylates and methacrylates yields substitution. The major side reaction is an intramolecular aldol-type condensation. Abstraction of an a-hydrogen from a methyl group of the polymer by either initiator or propagating carbanion yields an a-carbanion that attacks the carbonyl group of the adjacent repeat unit. 

M. Shi and Y.-L. Shi reported the synthesis and application of new bifunctional axially chiral (thio) urea-phosphine organocatalysts in the asymmetric aza-Morita-Baylis-Hillman (MBH) reaction [176, 177] of N-sulfonated imines with methyl vinyl ketone (MVK), phenyl vinyl ketone (PVK), ethyl vinyl ketone (EVK) or acrolein [316]. The design of the catalyst structure is based on axially chiral BINOL-derived phosphines [317, 318] that have already been successfully utilized as bifunctional catalysts in asymmetric aza-MBH reactions. The formal replacement of the hydrogen-bonding phenol group with a (thio)urea functionality led to catalysts 166-168 (Figure 6.51). 

Raspberry ketone is prepared by alkali-catalyzed condensation of the alkali salt of 4-hydroxybenzaldehyde and acetone, followed by selective hydrogenation of the double bond in the resulting 4-hydroxybenzalacetone. Other syntheses start from phenol which is converted into 4-(4-hydroxyphenyl)-2-butanone with methyl vinyl ketone (e.g., in the presence of phosphoric acid) [179] or with 4-hydroxy-2-butanone in the presence of concentrated sulfuric acid [180]. 

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