Olefination of Ketones

In contrast to aldehydes, simple ketones are poor substrates for Fe-catalyzed olefinations due to their weak electrophilicity. Decreasing the electron density of carbonyl group can facilitate olefination of ketones with diazo compounds. 

Despite the rich chemistry of 288 that may be anticipated, " " synthetic methods for this type of compounds are limited to the one involving oxidation of the corresponding alcohols. In contrast, 288 is readily derived from 287 by a simple and one-pot operation. Since propargylic alcohols are readily accessible from ketones or aldehydes, the straightforward transformation from 70 to 288f provides a novel method for carbonyl olefination of ketones and aldehydes. For example, ethisterone, 301, is tolerable to this transformation (route 2, Scheme 16) without any protection of the functional groups to give 302 (Equation (51))." ... 

Marko, I. E., Murphy, F., Kumps, L., Ates, A., Touillaux, R., Craig, D., Carballares, S., Dolan, S. Efficient preparation of trisubstituted alkenes using the Sml2 modification of the Julia-Lythgoe olefination of ketones and aldehydes. Tetrahedron 2001,57, 2609-2619. 

A new method for generating aldehydic enol ethers and enamines, which has some advantages over the large number of methods already available has been developed7 Although based on phosphonate olefination of ketones, the method involves use of dimethyl diazomethylphosphonate to generate a diazoalkene in the presence of alcohols or secondary amines (Scheme 15). Dimethyl diazomethyl-... 

Warren showed that olefination of ketones and aldehydes, or even esters, with phosphine oxide carbanions allows some control of stereochemistry in the alkene products. Reaction with an aldehyde or ketone generates diastereomeric P-hydroxyphosphine oxide products, which can be isolated and then chromatographically separated. Reaction of 573 with n-butyllithium was followed by addition of 3,4-methylenedioxy-benzaldehyde (574, known as piperonal) to give a 9 1 mixture of 575/576, the syn and anti alcohol, respectively.514 7i,e pyre syn alcohol 575 was isolated in 75% yield by chromatography on silica gel. 

Olefination Complexes of type (1) effect the olefination of ketones. Direction by a hydroxy group separated from the ketone by 2- or 3-carbons is observed. The reaction overwhelmingly favors the (EJ-isomers. 

The Nysted reagent, cyclo-dibromodi-g.-methylene(g-tetrahydrofuran)trizinc, is used for the olefination of ketones and aldehydes. 

The NHC-copper complexes were also compared to simple copper salts. Sometimes, Cu(I) salts surpassed or equaled NHC systems. However, for styrene derivatives or the olefination of ketones, the carbene species proved to have a better reactivity. 

A highly convenient method of generating trimethylsilylmethyl-lithium, a reagent for methylenation (Peterson olefination) of ketones and aldehydes, has been discovered. Transmetallation between the readily available (trimethylsilyl-methyl)tributyltin and n-butyl-lithium in a mixture of hexane and THF furnishes the reagent in quantitative yield at 0 °C in 30 min. ... 

Wittig olefination of ketone 49 with cyclopropylidenephosphorane afforded methylenecyclopropane 50. Subsequent cyclopropanation with dibromocarbene followed by debromination with zinc gave spiropentane 51. When 51 was treated with a rhodium catalyst under an atmospheric pressure of carbon monoxide, carbonylative skeletal rearrangement took place to give rise to the cyclopen-tenone 56. Mechanistically, the C4-C5 bond of spiropentane 51 adds oxidatively... 

Tab. 4.12. Olefination of ketones and aldehydes with a thioacetal-titanocene(ll) system.

The olefination of ketones to prepare trisubstituted alkenes employing Na-Hg affords moderate yields, unpredictable stereoselectivities and large amounts of retro-aldol products from the intermediate jS-alkoxy sulfones. High yields and moderate stereoselectivities of trisubstituted alkenes are obtained by a modification of the Julia-Lythgoe olefination reaction, involving the in situ capture of the intermediate y6-alkoxy sulfones with a... 

Simple unfunctionalized ketones such as aryl alkyl ketones 36 can be olefinated by ynolates to provide tetrasubstituted olefins 37-42 in good to excellent yield (Fig. 12) [56]. While the Wittig and the Horner-Emmons reagents are not suitable reagents for this type of olefination, especially for ferf-butyl phenyl ketone (43), the ynolate affords the corresponding olefin 41 in 74% yield (Fig. 13). Ynolates are actually much better reagents for the olefination of ketones than the conventional... 

Kiihn and coworkers [19] extended the MTO catalytic system to ketone substrates. Benzoic acid additive was needed to activate the ketones, a strategy that was first developed by Zhang and coworkers [20] in their investigation of olefination of unactivated ketones using an iron-based catalyst In contrast to the -selectivity observed for the iron-based system, MTO-catalyzed olefination of ketones favored Z-olefin products (Scheme 4). Up to 89/11 Z/ selectivity... 

Scheme 10 Acid-promoted olefination of ketones with EDA catalyzed by Fe(TPP)Cl...

A variety of pentacoordinated spirophosphoranes undergo olefination with aldehydes in the presence of t-BuOK to give a,p-unsaturated esters, amides, and nitriles with high Z selectivity (Scheme 46) [212, 217], This method has recently been extended to the Z selective olefination of ketones by modifying the pentacoordinated spirophosphoranes, which are readily prepared through the reaction of the corresponding P-H phosphoranes with a-halo carbonyl compounds in the presence of DBU [218],... 

Marko IE, Murphy F, Dolan S. Efficient preparation of tri-substituted alkenes using the Julia-Lythgoe olefination of ketones. On the key-role of Sml2 in the reductive ehmination step. Tetrahedron Lett. 1996 37(12) 2089-2092. 

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