Olefination of ketones and aldehydes

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. 

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. 

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

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. ... 

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

Small chiral organic molecules may catalyze the asymmetric addition of ketones, and aldehydes to electron-deficient olefins, such as vinylidene acetones, nitroole-fins, enones, and vinyl sulfones. In this chapter we will describe the inter- and intramolecular reactions in which activation of the carbonyl compound takes place via enamine formation. 

Another synthetically important photochemical reaction is the Paterno-Buchi reaction, i.e., the photocycloaddition of ketones and aldehydes to olefins. This is a milestone in organic photochemistry and involves attack of the n,ji triplet of the carbonyl compounds to an alkene in the ground state, mostly in the triplet multiplicity, although reactions via the singlet are well known. With nucleophilic olefins, the reaction occurs through the initial formation of a CO bond, in the opposite case, formation of a C-C bond occurs first. The use... 

A useful relative of the acyloin condensation is the McMurry olefination reaction. l in this reaction, ketones or aldehydes are treated with Ti(0) (TiCls + LiAlH4 TiCls + K TiCl3 + Li)2i5 to give alkenes.2 6 Reductive coupling is possible with a wide variety of ketones and aldehydes. i 3,217 Retinal (276), for example, was coupled with this reagent to give P-carotene (277) in 85% yield. ... 

Wang and coworkers synthesised recyclable and reusable pyrrolidine-fluorosulfonamide organocatalysts 3b,c. The fluorous sulfonamide organocatalyst 3b was used for the Michael addition of ketones and aldehydes to nitro-olefins in water, and the reaction gave products with high enantio- and diastereomeric purity. Robust organocatalyst 3b was easily separated from... 

Palladium-catalyzed oxidation of olefins to ketones, and aldehydes in certain cases. 

Catalytic oxidation of olefins to ketones and aldehydes 3.2.1. Wacker type oxidation of olefins... 

New C2-symmetric but axially unfixed organocatalysts (103) derived from L-proline catalyse Michael addition of ketones and aldehydes with nitro-olefins, in the presence of acidic additives such as benzoic acid. The excellent performance of up to 99/98/96% 0 on yiddldelee is ascribed to their likely bifunctional nature. (fA... 

A few years later, Tebbe and co-workers found that the methylene-bridged metallacycle 3, which has become known as the Tebbe reagent, is useful for the methylenation of ketones and aldehydes [5]. Titanocene-methylidene 4, the active species of this olefination, also transforms carboxylic acid derivatives into heteroatom-substituted olefins. Because the carbene complex 4 is much less basic than conventional olefination reagents such as phosphorus ylides, it can be employed for the olefination of carbonyl compounds possessing highly acidic a-protons or of highly hindered ketones, and has become an indispensable tool in organic synthesis. Various methods for the preparation of titaniumcarbonyl olefination. This chapter focuses on the use of metal-carbene complexes and some related species in carbonyl olefination (Scheme 4.2). 

In contrast to kinetic models reported previously in the literature (18,19) where MO was assumed to adsorb at a single site, our preliminary data based on DRIFT results suggest that MO exists as a diadsorbed species with both the carbonyl and olefin groups being coordinated to the catalyst. This diadsorption mode for a-p unsaturated ketones and aldehydes on palladium have been previously suggested based on quantum chemical predictions (20). A two parameter empirical model (equation 4) where - rA refers to the rate of hydrogenation of MO, CA and PH refer to the concentration of MO and the hydrogen partial pressure respectively was developed. This rate expression will be incorporated in our rate-based three-phase non-equilibrium model to predict the yield and selectivity for the production of MIBK from acetone via CD. 

The synthetic method leading to Nb-alkylidenes and Nb-alkylidynes was particularly successful, due to a quite remarkable difference in the reaction rate of 29 with ketones or aldehydes, vs the subsequent reaction of the alkylidene with ketones and aldehydes (see Scheme 37). The former reaction takes a few minutes at -40°C, while the latter one occurs in hours at room temperature.88 The reaction between 178 and benzaldehyde led to triphenylethylene and the niobyl derivative 184. Due to the difference in reaction rates between a and b in Scheme 37, it was found that the sequential addition of two different ketones or aldehydes to a THF solution of 29 produced a nonsymmetric olefin in a stepwise McMurry-type reaction.84 This is exemplified in the coupling shown in reaction c (Scheme 37). The proposed reaction pathway does not involve the intermediacy of a pinacolato ligand and therefore differs from the mechanism of the McMurry reaction and related reductive couplings at activated metal sites.89... 

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