McMurry reactions

Product 117 is a convenient starting compound for the subsequent modification of photochromes. Publication (09TL1614) gives an efficient synthetic route to both symmetrical 118 and unsymmetrical 119 phenyl-substituted dihetarylethenes bearing amino, hydroxy, or carboxy groups based on a Suzuki reaction of dichloride 117 with commercially available substituted boronic acids (or their pinacol esters) in a dimethyl ether (DME)-H20 mixture (4 1). For the symmetrical products, the yields are 85-95% for the unsymmetrical products, they are 60%. 

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Carbonyl Coupling Reactions (McMurry Reaction) (Smith Ch. 13.7.F)... 

Among the appHcations of lower valent titanium, the McMurry reaction, which involves the reductive coupling of carbonyl compounds to produce alkenes, is the most weU known. An excellent review of lower valent titanium reactions is available (195). Titanium(II)-based technology is less well known. A titanium(II)-based complex has been used to mediate a stetio- and regio-specific reduction of isolated conjugated triple bonds to the corresponding polyenes (196). 

Stoichiometric closure of furan and pyrrole cycles on McMurry reaction induced by low-valent transition metals 98PAC1071. 

Among the more recent name reactions in organic chemistry, the McMurry reaction is of particular importance as a synthetic method. It permits the... 

The intermolecular McMurry reaction is first of all a suitable method for the synthesis of symmetrical alkenes. With a mixture of carbonyl compounds as starting material, the yield is often poor. An exception to this being the coupling of diaryl ketones with other carbonyl compounds, where the mixed coupling product can be obtained in good yield. For example benzophenone and acetone (stoichiometric ratio 1 4) are coupled in 94% yield. ... 

As already discussed, low-valent titanium can be generated in situ from catalytic amounts of TiCls, by use of excess Zn powder and TCS 14 in acetonitrile, to cy-clize reductively 2-benzoylaminoacetophenone 2091 to the indole 2092, in 80% yield, in an elegant version of the McMurry reaction [23, 64]. Replacement of the Zn metal powder by Ti powder and TCS 14 is very effective - 2092 is obtained in 97% yield [64]. In these reactions the intermediate Ti(0)Cl is apparently recycled by MesSiCl 14 into TiCh [64]. In these Fiirstner versions of the McMurry reaction... 

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... 

Numerous furan-based porphyrins have been reported, such as tetraoxa[4n+2]porphyrin dications with 18ji-, 22n-, or 26ti-electron systems <00AG(E)1101>. The McMurry reaction... 

The proposed catalytic mechanism for intramolecular McMurry reaction begins with the reduction of TiCl3 by zinc metal to generate the activated titanium species A-19. Reductive cyclization of the dicarbonyl substrate forms the McMurry coupling product, along with titanium oxide complex B-15. To close the catalytic cycle, the oxide complex B-15 is converted to TiCl3 by Me3SiCl (Scheme 63).8d,8e... 

Scheme 12.13. Filrstner s McMurry reaction that is catalytic in titanium.

Metal alkylidene complexes find application in the metathesis of alkenes, the cvclopropanation of alkenes (Grubbs, Schrock), Wittig type reactions, and the McMurry reaction. In suitable complexes a-elimination can occur twice yielding alkylidync complexes. See Figure 2.21 for an example with tungsten. 

The McMurry reaction (the reductive dimerization of carbonyl compounds giving olefins after treatment with the low-valent titanium reagents TiCla/Mg and TiCla/Zn in THF at 40°C) (CR891513) is a key step in the synthesis of photochromic cyclopentene derivatives. Later, it has been shown that TiCU, which is easier to handle than TiCls, can be used. The cyclization products are formed in 50-60% yields (98S1092,03EJO155). The advantages of this method are that the reactions can be scaled and inexpensive starting materials can be used. 

The McMurry reaction also gave new multiphotochromic dithieny-lethenes 145 and 146 containing an N-substituted dihydropyrrole bridge... 

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