Ketones alkene derivatives

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]. 

Aromatic aldehydes and ketones react with carbanions to yield aryl-suhstituled alkene derivatives. 

Similarly, for alkenes derived from saturated methyl ketones the regioselectivity is determined by starting hydrazone ( ) (Z) ratios in some solvents but not in others. Thus 2-octanone trisylhydrazone, which is an inseparable 85 15 mixture of ( )- and (Z)-isomers, gives an 85 15 ratio of l-octene 2-octene if vinyllithium formation is carried out in THF, but a 98 2 ratio of the same products when 10% TMEDA-hexane is the solvent. The implication of this observation is that in THF the regioselectivity is determined by azomethine stereochemistry but that in TMEDA-hexane it is not. Note, however, that in this case a iyn-directing effect does not occur in TMEDA, whereas in the previous example it does. Thus more than 10 years after it was asserted that a detailed explanation of the observed solvent dependencies...await further studies owing to the complexities of the reaction system. , little headway has been made. 

Ketones and 1,2-diketones are readily converted into alkynes, which can subsequently be reduced to alkenes. Since there are a number of methods to reduce alkynes stereoselectively, this route offers a method of controlling the stereochemistry of acyclic alkenes derived from ketone starting materials. The most common approach for the ketone to alkyne transformation has been conversion of the starting ketone into a vicinal dichloride and subsequent bis elimination induced by strong base. ... 

Reduction of organic substrates to dianions can be divided into (a) reductions of polycyclic aromatics, (b) reductions of aryl-substituted alkenes or alkynes, (c) reductions of 4n 7i-electron systems, and (d) reduction of aryl ketones and derivatives. 

Tosylhydrazones of aliphatic aldehydes and ketones react with a base in an aprotic solvent at 90-180 C to give diazo compounds which undergo thermal decomposition with loss of nitrogen to yield alkenes derived from hydrogen migration and cyclopropanes from intramolecular insertion. In proton donor solvents decomposition of y-tosylhydrazones by base occurs primarily by a cationic mechanism involving diazonium and/or carbenium ion intermediates. 

Conversion of 1-Cyciopropyl-l-hydroxy-l-alkene Derivatives to Cyclopropyl Ketones... 

Compound I is a ketone, II is a primary alcohol, III is a primary alcohol of alkene derivation and IV is an ether derivative. 

Ketone-Alkene Coupling Reactions. Ketyl radicals derived fromreduction of ketones or aldehydes with Sml2 may be coupled both inter- and intramolecularly to a variety of alkenic species. Excellent diastereoselectivities are achieved with intramolecular coupling of the ketyl radical with Q ,/3-unsaturated esters. In the following example, ketone-alkene cyclization took place in a stereocontrolled manner established by chelation of the resulting Sm(III) species with the hydroxyl group incorporated in the substrate (eq 22). ... 

In connection with studies on the synthesis of complex cell wall glycans, we have developed effective syntheses of the novel branched sugar aceric acid and its C-2 epimer. Control of asymmetry in the installation of the key tertiary centers was effected by either asymmetric dihydroxylation of an appropriate alkene derivative or by thiazole addition to the corresponding ketone. 

The asymmetric a-sulfenylation of ketones is a particularly challenging reaction, as demonstrated by the poor success reported in the stereoselective variants via classical enolate/azaenolate reaction with an electrophilic sulfur reagent [71]. An umpolung approach has been devised by Coltart and co-workers [72] to effect the first asymmetric a-sulfenylation of ketones with arene thiols. Nitroso alkene derivatives, in i/tM-generated under basic conditions from a-chloro oximes, reacted with arene thiols in the presence of cinchona thiourea 27, which promoted the conjugate addition of thiophenol (Scheme 14.25). The chiral nonracemic a-sulfenylated oximes were directly hydrolyzed by IBX to ketones in high yield and good enantioselectivity. 

Other examples have been given of the preparation of branched-chain and extended-chain alkenes by application of Wittig reagents to sugar aldehydes and ketones,and the mass spectra of alkenes derived from 1,2 5,6-di-O-iso-propylidene-D-r/Z o-hexos-3-ulose have been described.Compound (25) was... 

Only one previous method exists for the replacement of a -hydrogen atom of a conjugated enone by an electrophilic substituent. Now treatment of aj8-unsaturated aldehydes and ketones with triphenylthioborate has been shown to provide 1,3-bis(phenylthio)alkene derivatives, the anions of which are effective /S-acyl vinyl anion equivalents (Scheme 51). ... 

In 1996 Yang first reported the asymmetric epoxidation of olefins mediated by a symmetric dioxirane generated from the corresponding ketone [22]. The chiral ketone was derived from BINAP, and exhibited enantioselectivities typically between 5% and 50% ee under stoichiometric conditions, and 87% ee in the epoxidation of trans-4,4 - diphenylstilbene. With modification of the original C2 symmetric ketone and development of the reaction to run catalytically, Yang was able to increase the enantioselectivity of the process [23, 24], With very hindered alkenes, such as frans-4,4 -diterf-butylstilbene, enantioselectivities of up to 95% ee were achieved (Scheme 1.9). 

Thallium(III) acetate reacts with alkenes to give 1,2-diol derivatives (see p. 128) while thallium(III) nitrate leads mostly to rearranged carbonyl compounds via organothallium compounds (E.C. Taylor, 1970, 1976 R.J. Ouelette, 1973 W. Rotermund, 1975 R. Criegee, 1979). Very useful reactions in complex syntheses have been those with olefins and ketones (see p. 136) containing conjugated aromatic substituents, e.g. porphyrins (G. W. Kenner, 1973 K.M. Smith, 1975). 

The isoflavone 406 is prepared by the indirect a-phenylation of a ketone by reaction of phenylmercury(II) chloride with the enol acetate 405, prepared from 4-chromanone[371]. A simple synthesis of pterocarpin (409) has been achieved based on the oxypalladation of the oriho-mercurated phenol derivative 408 with the cyclic alkene 407[372,373]. 

Thallation of aromatic compounds with thallium tris(trifluoroacetate) proceeds more easily than mercuration. Transmetallation of organothallium compounds with Pd(II) is used for synthetic purposes. The reaction of alkenes with arylthallium compounds in the presence of Pd(Il) salt gives styrene derivatives (433). The reaction can be made catalytic by use of CuCl7[393,394], The aryla-tion of methyl vinyl ketone was carried out with the arylthallium compound 434[395]. The /9-alkoxythallium compound 435, obtained by oxythallation of styrene, is converted into acetophenone by the treatment with PdCh[396]. 

The trisannulation reagent 7-acetoxy-l,l l-dodecadien-3-one (134) is derived from the bisannulation reagent 124 in four steps. This reagent is a synthetic equivalent of l-dodecene-3,7,11-trione, and the two ketone groups of the trione are masked as an acetoxy and a terminal alkene. The synthesis of optically active D-homo-19-norandrosta-4-en-3-one (135) by the trisannulation reaction... 

Raw Material and Energy Aspects to Pyridine Manufacture. The majority of pyridine and pyridine derivatives are based on raw materials like aldehydes or ketones. These are petroleum-derived starting materials and their manufacture entails cracking and distillation of alkanes and alkenes, and oxidation of alkanes, alkenes, or alcohols. Ammonia is usually the source of the nitrogen atom in pyridine compounds. Gas-phase synthesis of pyridines requires high temperatures (350—550°C) and is therefore somewhat energy intensive. 

Various methods have been employed to overcome this difficulty. For example, a method used by Chemical Abstracts involves naming the dihydro derivative of the heterocyclic ketone (or imine or exocyclic alkene) form, and adding the words mesoionic didehydro derivative (example 131). A similar approach, favoured by Ollis (76AHQ19)1), involves naming the corresponding cation hydroxide, with the prefix anhydro (indicating removal of the elements of water) (example 132). 

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