McMurry olefination reaction / coupling

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. ... 

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... 

McMurry olefin synthesis. Lenoir has published a variation of the McMurry reaction for reductive coupling of ketones (6, 589). The actual reagent presumably is also TiCl2, but is produced by reduction of TiCU in THF or dioxane with zinc. This reagent in the presence of pyridine converts ketones into tetrasubstituted alkenes. The reaction is most satisfactory with symmetrical ketones mixtures of (E)- and (Z)-isomers obtain from unsymmetrical ketones, with the latter predominating. Strongly hindered ketones are reduced by the reagent to the secondary alcohol. 

The olefin metathesis of 3-hydroxy-4-vinyl-l,2,5-thiadiazole 112 and a McMurry coupling reaction (Ti3+ under reductive conditions) of the aldehyde 114 were both unsuccessful <2004TL5441>. An alternative approach via a Wittig reaction was successful. With the use of the mild heterogenous oxidant 4-acetylamino-2,2,6,6-tetramethyl-piperidine-l-oxoammonium perfluoroborate (Bobbitt s reagent), the alcohol 113 was converted into the aldehyde 114. The phosphonium salt 115 also obtained from the alcohol 113 was treated with the aldehyde 114 to give the symmetrical alkene 116 (Scheme 16) <2004TL5441>. 

It is difficult to obtain cross-coupling products of two different carbonyl compounds by an intermolecular version of the McMurry reaction. Examples that use excess amounts of one carbonyl component are few. "" When one carbonyl component is replaced by a 1,1-dihalo compound or dithioacetal and the alternative is reduced with a low-valent metal such as low-valent titanium or chromium(ii), cross-coupling products, that is, Wittig-type olefins, are produced in high yields. Because the alternative approach is described elsewhere, we concentrate on only its important features here. 

Ephritikhine, M. Villiers, C. The McMurry Coupling and Related Reactions. In Modem Carbonyl Olefination-, Takeda, T., Ed. Wiley-VCH ... 

In 1973 Mukaiyama, Tyrlik, and McMurry discovered a remarkably simple reaction that couples aldehydes or keto compounds reductively to olefins [1, 2]. This methodology following eq. (1) differs from that of Section 3.2.10 in that no extra methylene or alkylidene transfer reagent is required. The stereochemistry of the product depends on the nature of the substituents R and whether an open-chain or a cyclic olefin results. 

The twofold extrusion of nitrogen and sulfur and selenium and sulfur from 1-thia- and l-selena-3,4-diazolines(77), readily available from the reaction of diazoalkanes with thio- and selenaketones, respectively, as well as from the reductive coupling of carbonyl compounds such as 78, is the preferred method for preparation of olefins of type I and II (98,99). Examples of the extrusion method, developed by Barton (100), and the McMurry reaction (101) are given in Scheme 1. 

Beller et al. have shown for the first time that palladium colloids are effective catalysts for the olefination of aryl bromides (Heck reaction). Reetz et al. have studied Suzuki and Heck reactions catalyzed by preformed palladium clusters and palladium/nickel bimetallic clusters and further progress was achieved by Reetz and Lohmert using propylene carbonate stabilized nanostructured palladium clusters as catalysts in Heck reactions. In addition, the use of nanostructured titanium clusters in McMurry-type coupling reactions has been demonstrated by Reetz et... 

The preparation of the PPV skeleton can be generally classified into two main strategies (i) olefinations methods to prepare the vinylene double bond and (ii) transition-metal-catalyzed single bond formation between the arene and vinylene components. The former includes Wittig-, Wittig-Horner- and Knoevenagel-type condensations, whereas the latter approach was demonstrated via Heck, Stille, Suzuki Miyaura and McMurry coupling reactions (Scheme 7.5). 

W. J. Scott and J. E. McMurry, Acc. Chem. Res., 1988, 21, 47-54. Olefin Synthesis Via Organometallic Coupling Reactions of Enol Triflates. 

A titanium(Il) species formed from titanium trichloride and lithium aluminum hydride is a useful reagent for the reductive coupling of carbonyl compounds to olefins (McMurry, 1974 McMurry and Fleming, 1974). Both aliphatic and aromatic ketones can be converted to tetrasubstituted olefins in excellent yields. Reductive dimerization of retinal (CCLXXFV) affords j6-carotene (CCLXXV) in 85% yield. The course of the reaction can be accounted for by assuming pinacol formation followed by loss of titanium dioxide. 

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