Vinyl ketone complex

The complex OsH(OH)(CO)(P Pr3)2 also reacts with methyl acrylate, methyl vinyl ketone, and allyl alcohol.91 Reaction with methyl acrylate leads to OsH(OH) (COXrf-CH2=CHC02MeXP Pr3)2 containing the olefin trans to the hydride ligand. In solution, this complex releases the olefin to generate the starting complex. The thermodynamic magnitudes involved in the equilibrium have been determined in toluene-t/a by 31P 1H NMR spectroscopy. The values reported are AH° = 17.0 0.5 kcal-mor1 and AS° = 54.0 1.2 cal-K 1-mol 1. In the presence of the methyl vinyl ketone complex OsH(OH)(CO)(P Pr3)2 affords 0sH CHCHC(0) Me (CO)(P Pr3)2 and water, whereas in the presence of allyl alcohol the loss of... 

Similar Ru-O coordination has been observed in both the crystal structure of an r -methyl vinyl ketone complex [34] and in the DFT calculations of a ruthenium ester carbene by Parker, Sampson, and co-workers [35]. The stability of the ester carbene intermediate led to the inactivity of a 1-substituted cyclobutene ester in the formation of homopolymers via ROMP (ring-opening metathesis polymerization) (Scheme 7.2) [36]. 

Figure 1.2. Endo and exo pathway for the Diels-Alder reaction of cyclopentadiene with methyl vinyl ketone. As was first noticed by Berson, the polarity of the endo activated complex exceeds that of the exo counterpart due to alignment of the dipole moments of the diene and the dienophile K The symmetry-allowed secondary orbital interaction that is only possible in the endo activated complex is usually invoked as an explanation for the preference for endo adduct exhibited by most Diels-Alder reactions.

The carbopalladation of allylamine with malonate affords the chelating complex 510, which undergoes insertion of methyl vinyl ketone to form the amino enone 511[463]. The allylic sulfide 512 has the same chelating effect to give the five-membered complex 513 by carbopalladation[463.464]. 

The second group of reactions is called vicinal difunctionalization. They embrace the C2 and C3 positions of the furan ring simultaneously. Thus, complex 3 (X = O, R = R = R = H) reacts with benzaldehyde dimethyl acetal to give 4H-furanium cation (the product of electrophile addition at C4), which experiences further attack by the methoxide group with formation of the acetal 8 (950M2861). This reaction is possible in the presence of the Lewis acid (BF3—OEt2). Reaction with methyl vinyl ketone in methanol, when run in identical conditions. 

The rate of oxidation/reduction of radicals is strongly dependent on radical structure. Transition metal reductants (e.g. TiMt) show selectivity for electrophilic radicals (e.g. those derived by tail addition to acrylic monomers or alkyl vinyl ketones - Scheme 3.89) >7y while oxidants (CuM, Fe,M) show selectivity for nucleophilic radicals (e.g. those derived from addition to S - Scheme 3,90).18 A consequence of this specificity is that the various products from the reaction of an initiating radical with monomers will not all be trapped with equal efficiency and complex mixtures can arise. 

Seven-membered carbocycles are also available from the reaction of alkenylcarbene complexes of chromium and lithium enolates derived from methyl vinyl ketones [79b] (Scheme 65). In this case, the reaction is initiated by the 1,2-addition of the enolate to the carbene complex. Cyclisation induced by a [1,2]-migration of the pentacarbonylchromium group and subsequent elimination of the metal fragment followed by hydrolysis leads to the final cyclo-heptenone derivatives (Scheme 65). 

In principle, numerous reports have detailed the possibility to modify an enzyme to carry out a different type of reaction than that of its attributed function, and the possibility to modify the cofactor of the enzyme has been well explored [8,10]. Recently, the possibility to directly observe reactions, normally not catalyzed by an enzyme when choosing a modified substrate, has been reported under the concept of catalytic promiscuity [9], a phenomenon that is believed to be involved in the appearance of new enzyme functions during the course of evolution [23]. A recent example of catalytic promiscuity of possible interest for novel biotransformations concerns the discovery that mutation of the nucleophilic serine residue in the active site of Candida antarctica lipase B produces a mutant (SerlOSAla) capable of efficiently catalyzing the Michael addition of acetyl acetone to methyl vinyl ketone [24]. The oxyanion hole is believed to be complex and activate the carbonyl group of the electrophile, while the histidine nucleophile takes care of generating the acetyl acetonate anion by deprotonation of the carbon (Figure 3.5). 

Both MeMn(CO)5 and PhMn(CO)5 react with acetylenes to yield vinyl ketone tetracarbonyl complexes, most likely via a pathway involving CO insertion [Eq. (18)] 14, 36). Reactions of these same alkyls with 1,3-dienes may proceed similarly 16, 95, 96). The chelating ligand o-styryldiphenyl-phosphine (L—L) converts MeMn(CO)j into two products 25) whose structures (XXII and XXIII) were elucidated by X-ray crystallography 24). An unusual migration of COMe onto L—L occurs subsequently to the initial insertion step. 

Reactions of the hydrido(hydroxo) complex 2 with several substrates were examined (Scheme 6-14) [6]. The reactions are fairly complicated and several different types of reachons are observed depending on the substrate. Methyl acrylate and small Lewis bases such as CO, P(OMe)3, BuNC coordinate to the five-coordinated complex 2 affording the corresponding six-coordinate complexes. In reactions with the unsaturated bonds in dimethylacetylenedicarboxylate, carbon dioxide, phenylisocyanate indications for the addition across the O-H bond but not across the Os-OH bond were obtained. In reactions with olefins such as methyl vinyl ketone or allyl alcohol, elimination of a water molecule was observed to afford a hydrido metalla-cyclic compound or a hydrido (ethyl) complex. No OH insertion product was obtained. 

Trost et al 2 briefly explored using non-enone enophiles. Simple alkenes led to the formation of complex mixtures of isomers due to the presence of an additional set of /3-hydrogens. Many other types of substrates were incompatible with reaction conditions. Vinyl ketones were, therefore, the only coupling partners shown to be effective in the ruthenium-catalyzed Alder-ene couplings of allenes and alkenes. 

A closer examination by ex situ analysis using NMR or gas chromatography illustrates that intrazeolite reaction mixtures can get complex. For example photooxygenation of 1-pentene leads to three major carbonyl products plus a mixture of saturated aldehydes (valeraldehyde, propionaldehyde, butyraldehyde, acetaldehyde)38 (Fig. 33). Ethyl vinyl ketone and 2-pentenal arise from addition of the hydroperoxy radical to the two different ends of the allylic radical (Fig. 33). The ketone, /i-3-penten-2-one, is formed by intrazeolite isomerization of 1-pentene followed by CT mediated photooxygenation of the 2-pentene isomer. Dioxetane cleavage, epoxide rearrangement, or presumably even Floch cleavage130,131 of the allylic hydroperoxides can lead to the mixture of saturated aldehydes. 

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. 

Brown proposed a mechanism where the enolate radical resulting from the radical addition reacts with the trialkylborane to give a boron enolate and a new alkyl radical that can propagate the chain (Scheme 24) [61]. The formation of the intermediate boron enolate was confirmed by H NMR spectroscopy [66,67]. The role of water present in the system is to hydrolyze the boron enolate and to prevent its degradation by undesired free-radical processes. This hydrolysis step is essential when alkynones [68] and acrylonitrile [58] are used as radical traps since the resulting allenes or keteneimines respectively, react readily with radical species. Maillard and Walton have shown by nB NMR, ll NMR und IR spectroscopy, that tri-ethylborane does complex methyl vinyl ketone, acrolein and 3-methylbut-3-en-2-one. They proposed that the reaction of triethylborane with these traps involves complexation of the trap by the Lewis acidic borane prior to conjugate addition [69]. 

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. 

The activation of various reactions by Lewis acids is now an everyday practice in synthetic organic chemistry. In contrast, solvent effects on Lewis acid catalysed Diels-Alder reactions have received much less attention. A change in the solvent can affect the association step leading to the transition structure. Ab initio calculations on the Diels-Alder reaction of cyclopentadiene and methyl vinyl ketone in aqueous media showed that there is a complex of the reactants which also involves one water molecule119. In an extreme case solvents can even impede catalysis120. The use of inert solvents such as dichloromethane and chloroform for synthetic applications of Lewis acid catalysed Diels-Alder reactions is thus well justified. General solvent effects, in particular those of water, will be discussed in the following section. 

Figure 7.3 Standard Gibbs energies of transfer for reactants and activated complex for the Diels-Alder reaction of cyclopentadiene ( , ) with ethyl vinyl ketone (2, A) from 1-PrOH to 1-PrOH-water as a function of the mole fraction of water initial state (1 + 2, ) activated complex (o).

The dimerization of functional alkenes such as acrylates and acrylonitrile represents an attractive route to obtain bifunctional compounds such as dicarboxylates and diamine, respectively. The head-to-tail dimerizahon of acrylates and vinyl ketones was catalyzed by an iridium hydride complex generated in situ from [IrCl(cod)]2 and alcohols in the presence of P(OMe)3 and Na2C03 [26]. The reaction of butyl acrylate 51 in the presence of [IrCl(cod)]2 in 1-butanol led to a head-to-tail dimer, 2-methyl-2-pentenedioic acid dibutyl ester (53%), along with butyl propionate (35%) which is formed by hydrogen transfer from 1-butanol. In order to avoid... 

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