Other Unsaturated Aldehydes and Ketones

Other Unsaturated Aldehydes and Ketones.—A full paper has been published describing the preparation of /3y-unsaturated aldehydes from allyl halides through 

Reagents i, R COCHN2 ii, MeaSiCl, EtsN iii, HIO4, MeOH, H2O 

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Welti (9). The quality of the spectra is uniformly good as exemplified retention times are C02, H20, formaldehyde, acetaldehyde, methanol, propylene, isobutylene, acetone, hexene, and other unsaturated aldehydes and ketones. The actual chemical structures of these ketones and of several other products are being determined by mass spectrometry. 

IV. Reduction of Other Unsaturated Aldehydes AND Ketones with Ethyl Alcohol... 

An uncertainty of 40% should be attached to these measurements. Sato et al. (2004) compared the experimental results for these and other unsaturated aldehydes and ketones with results of conventional transition state theory, based on ab initio and density functional electronic structure calculations. They found that the differences in the rate coefficients derived from differences in activation energies, rather than significant changes in the A factors. 

When unsymmetrical ketones were used in this reaction (with BF3 as catalyst), the less highly substituted carbon preferentially migrated. The reaction can be made regioselective by applying this method to the a-halo ketone, in which case only the other carbon migrates. The ethyl diazoacetate procedure has also been applied to the acetals or ketals of a, P-unsaturated aldehydes and ketones. ... 

Aluminium isopropoxide is a specific reagent for the reduction of carbonyl group to hydroxyl group. Since it reduces the carbonyl group in presence of other reducible groups like nitro or a double bond which remain unaffected, aluminium isopropoxide is largely employed for the reduction of unsaturated aldehydes and ketones. 

Double bonds conjugated with aromatic rings and with carbonyl, carboxyl, nitrile and other functions are readily reduced by catalytic hydrogenation and by metals. These reductions are discussed in the appropriate sections aromatics, unsaturated aldehydes and ketones, unsaturated acids, their derivatives, etc. 

Over the last five years, we have designed, synthesized, and applied new ligands for asymmetric 1,2- and 1,4-addition reactions. Suitable ligands were found for the addition of alkyl-, aryl-, and alkenylzinc reagents to a,(3-unsaturated aldehydes and ketones, a-branched and unbranched aliphatic aldehydes, and imines. Although some substrates such as ketones and other carbonyl compounds have remained a challenge, we believe that this system provides an excellent entry into various classes of chiral intermediates. Application of these synthesized complex molecules is the current pursuit in our laboratories. 

Ge, Sn) double-bond compounds, while benzaldehyde or benzophenone react with M=N double bonds to give the corresponding [2 -f 2] adducts regioselectively with the formation of M-O bonds. In addition, the [4 + 2] cycloaddition reaction of azametaUenes and phosphametallenes with a,/3-unsaturated aldehydes and ketones have been reported to give the six-membered ring compounds. Other cycloaddition using 1,3-dipoles such as nitrileoxide and azide derivatives were reported. The reactivities of M=E double bond are summarized in Scheme... 

On the other hand, unsaturated aldehydes and ketones were obtained using allylic alcohols as alkene components [68]. Similarly, allyl f-butyldimethylsilyl ether and N-allylamides gave silyl enol ethers [69] and enamides [70], respectively. The ruthenium-catalyzed alkene-alkyne coupling was successfully combined with the palladium-catalyzed intramolecular asymmetric allylic alkylation [71] to provide a novel one-pot heterocyclization method [72]. 

Indeed, a combination of tributyltln hydride, Pd° catalyst and a weak acid, such as ammonium chloride, forms an effective, yet mild tool for conjugate reduction of a, -unsaturated aldehydes and ketones. Similar results are obtained with other acidic cocatalysts, such as zinc chloride, acetic acid and tributyltln triflate. With this system, reductions occur with high regloselectivity, providing a useful approach for deuterium incorporation into either the P- or a-position by using either tributyltln deu-teride or D2O, respectively (Scheme 57). ... 

Scheme 6.26. Auxiliary-based asymmetric cyclopropanations (addition of CH2 ) of a, 3-unsaturated aldehydes and ketones, (a) [98] (b) [99,100] (c) [101-104] (d) Proposed transition structures [104]. Only one zinc and the transfer methylene are shown other atoms associated with the Simmons-Smith reagent are deleted for clarity.

The use of ethyl alcohol for the selective reduction of the carbonyl group in unsaturated aldehydes and ketones other than acrolein is illustrated in Table V. Here also, the data listed are the best obtained in a limited number of runs with each compound and do not necessarily represent optimum conditions. As previously stated, in the acrolein-allyl alcohol reaction a small amount of propyl alcohol is found in the products. This side reaction appears to be considerably more important with crotonaldehyde, since the C4 alcohol fraction here contained 27 % butyl alcohol. The relatively high conversion to saturated alcohol is believed to be due in part to unfavorable reaction conditions. With methacrolein and with methyl isopropenyl ketone the saturated alcohol amounted to 5 % of the imsaturated alcohol produced. 

Even in the presence of other silicon reagents like PhjSiHj, Michael acceptors are totally unaffected. The addition of catalytic amounts of zinc chloride to the Pd(0)/silane system, however, creates a three-component mixture that allows rapid conjugate reduction of a,p-unsaturated aldehydes and ketones. The conjugate reduction was shown to be both regio- and stereoselective. The use of dideuterodiphenylsilane in the reduction of unsaturated ketones yielded satmated ketones containing one deuterium atom at the P-position. On the other hand, when traces of D2O were added to the nondeuterated mixture, incorporation of deuterium occurred in the a-position (Scheme 16). ... 

First, in common with other conjugated rr-electron systems that we have seen, a,p-unsaturated aldehydes and ketones are more stable than their nonconjugated isomers. Under conditions chosen to bring about their interconversion, for example, the equilibrium between a p,y-unsaturated carbonyl and its a,p-unsaturated analog favors the conjugated isomer. 

Chemically, the diminished rr-electron density in the double bond makes a,P-unsaturated aldehydes and ketones less reactive than alkenes toward electrophilic addition. Nucleophilic addition the other hand, can involve either the carbonyl group or the a,p double bond. 

Unsaturated Dithioketene Acetals. The reaction of anion (1) with various o ,/3-unsaturated aldehydes and ketones occurs in a 1,2-fashion and provides vinyl thioketene acetals that are acceptable dienes for Diels-Alder reactions (eq 11) dienes of this type are difficult to access using other protocols. This method is also convenient for the introduction of a protected carbonyl group. 

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