Ketone alkenation

When pyrolyzed, P-hydroxy alkenes cleave to give alkenes and aldehydes or ketones. Alkenes produced this way are quite pure, since there are no side reactions. The mechanism has been shown to be pericyclic, primarily by observations... 

As stoich. [Ru(0)((N 0)p7CH3CN it oxidised primary alcohols to aldehydes, secondary alcohols to ketones, alkenes to aldehydes, tetrahydrofuran to y-butyrolactone. Styrene, cis- and tran -stilbenes gave benzaldehyde and adamantane gave 1-adamantol exclusively, while cyclohexanol gave cyclohexanone, suggesting that the complex is an effective oxidant for unactivated C-H bonds [636]. Immobilisation of the catalyst within Nation films on a basal plane pyrohtic graphite electrode was achieved, but the... 

Notes A useful reagent in that one can titrate the oxidation. Primary alcohols are converted to acids secondary alcohols to ketones alkenes and alkynes are resistant. Related reagents ... 

Table 1 Palladium(II)-catalyzed Oxidation of Functionalized Terminal Alkenes to Methyl Ketones Alkene Product...

When the enthalpies of reaction between branched ketones and the corresponding 1,1-disubstituted alkenes are calculated using the multiple enthalpies of formation available for the latter, the following ranges are obtained Me/i-Pr, 196.6 to 200.5 Et/i-Pr, 201.2 to 206.6 and Me/t-Bu, 200.5 to 205.1 kJmol-1. Perhaps it is reasonable to conclude that the reaction enthalpies for the branched compounds either will be approximately constant, as for the unbranched ketone/alkene conversions, or will be more endothermic with branching, as in the branched aldehyde/alkene conversions. In either case, the least endothermic reaction enthalpy for the Me/i-Pr conversion above seems inconsistent and therefore the enthalpies of formation for 2,3-dimethyl-l-butene from References 16 or 26, which are essentially identical, should be selected. These enthalpies were also selected in a previous section. However, there is too much inconstancy, as well as too much uncertainty, in the replacement reactions of carbonyls and olefins to be more definitive in our conclusions. 

Organic electroreductions at mercury cathodes in tetraalkylammonium (TAA+) electrolyte solutions at the limit of the cathodic potential window are described. Aromatic hydrocarbons, fluorides, ethers and heterocycles, as well as aliphatic ketones, alkenes and alkynes have been studied, using both aqueous and non-aqueous solvents. At these very negative potentials neither the TAA+ cation nor the mercury cathode are inert, instead they combine to form TAA-mercury. It is hypothesized, and supporting evidence is presented, that TAA-mercury serve as mediators in the organic electroreductions. The mediated reactions show remarkable selectivity in certain cases and it is shown that this selectivity can be improved by the choice of the TAA +. 

Reduction is an important reaction for the metabolism of compounds that contain reducible groups, such as aldehydes, ketones, alkenes, nitro groups,... 

Nevertheless, the use of chirally modified Lewis acids as catalysts for enantioselective aminoalkylation reactions proved to be an extraordinary fertile research area [3b-d, 16]. Meanwhile, numerous publications demonstrate their exceptional potential for the activation and chiral modification of Mannich reagents (generally imino compounds). In this way, not only HCN or its synthetic equivalents but also various other nucleophiles could be ami-noalkylated asymmetrically (e.g., trimethylsilyl enol ethers derived from esters or ketones, alkenes, allyltributylstannane, allyltrimethylsilanes, and ketones). This way efficient routes for the enantioselective synthesis of a variety of valuable synthetic building blocks were created (e.g., a-amino nitriles, a- or //-amino acid derivatives, homoallylic amines or //-amino ketones) [3b-d]. 

The hydrides are reactive and readily react with halogenocarbons, alcohols, and ketones alkenes afford alkyls. 

Although the Wittig reaction (section 4.3.1) and its modified versions provide highly effective and general methods for the aldehydes and ketones alkenation, there are several drawbacks in their use. To overcome these drawbacks, new methods which employ the transition metal complex reagents " as catalysts have been developed. A variety of catalytic aldehyde alkenation reactions have been reported with Mo catalyst other metals such as Re, Ru, Rh and Fe are also established as useful catalysts. Very mild conditions are required for catalytic alkenation short reaction times and high selectivities are generally observed. 

Oxidation of alcohols and aldehydes. Primary alcohols and aldehydes are oxidized to the corresponding acids in good yield by this reagent, which can be used in catalytic amounts in the presence of excess oxidant for regeneration. Secondary alcohols afford ketones alkenes and tertiary alcohols do not react. ... 

When pyrolyzed, p-hydroxy alkenes cleave to give alkenes and aldehydes or ketones." Alkenes produced this way are quite pure, since there are no side reactions. The mechanism has been shown to be pericyclic, primarily by observations that the kinetics are first order" and that, for ROD, the deuterium appeared in the allylic position of the new alkene." This mechanism is the reverse of that for the oxygen analog of the ene synthesis (16-54). p-Hydroxyacetylenes react similarly to give the corresponding allenes and carbonyl compounds." " The mechanism is the same despite the linear geometry of the triple bonds. 

A much more highly diastereoselective process results when alkenic 3-keto ester and 3-ketoamide substrates can be utilized in the ketone-alkene reductive coupling process. Both electron deficient and unactivated alkenes can be utilized in the reaction (equations 65 and 66). In such examples, one can take advantage of chelation to control the relative stereochemistry about the developing hydroxy and car-boxylate stereocenters. Favorable secondary orbital interactions between the developing methylene radical center and the alkyl group of the ketyl,and/or electrostatic interactions in the transition state account for stereochemical control at the third stereocenter. 

Curiously, the relative stereochemistry between the carboxylate and the adjacent hydroxy group in the Sml2-mediated intramolecular pinacolic coupling reaction is opposite to that observed in the intramolecular Barbier reactions and ketone-alkene reductive coupling reactions discussed previously (compare... 

A further, more complicated example of the stereoselective reductive ketone-alkene coupling is shown in the samarium diiodide promoted cyclization of unsaturated ji-oxo estersl2, giving 1.2,3-trialkyl-2-hydroxycyclopentanecarboxylates. The configuration of the two newly formed stereogcnic centers is determined by chelation of the intermediate radical by samarium(III). 

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