Coupling reactions McMurry

Highly strained cyclic compounds are accessible by an intramolecular variant. An instructive example for the synthetic potential of the McMurry coupling reaction is the synthesis of 3,3-dimethyl-1,2-diphenylcyclopropene 8 ... 

Oda et al. recently reported the synthesis of the highly strained trimeric meta-PAM 139 (Scheme 32) [82]. The required triene 140 was prepared from a,m-dial-dehyde 141 by an intramolecular McMurry coupling reaction. Bromination/dehy-drobromination of 140 furnished 139 as moderately stable, colorless crystals which decomposed above 180°C. The greater degree of strain in 139 compared to... 

Covalent attachment of adamantane molecules is a key strategy to string them together and construct molecular rods. The McMurry coupling reaction was employed to obtain polyadamantane molecular rods (see Fig. 35) [170]. As another example, synthesis of tetrameric 1,3-adamantane and its butyl derivative has been reported [171] (see Fig. 36). 

McMurry coupling reaction. The mechanism of the McMurry coupling reaction consists of two defined steps the reductive dimerization of the... 

A McMurry coupling reaction involving 3-aza-1,5-dicarbonyl compounds gave 2,5-dihydro-3,4-diarylpyrroles <06SL490>. The latter were converted into the corresponding 3,4-diarylpyrroles by irradiation (Hg lamp, 500 W) in acetonitrile. 

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>. 

McMurry coupling. Reaction of TiCl3 with C8K at 150-160° provides a finely dispersed form of the metal on graphite, which effects coupling of aldehydes or... 

Disubstituted cyelopropenes. The McMurry coupling reaction is convenient for preparation of 3,3-disubstituted cyclopropenes of type 3 and 4, even, though these products are considerably strained (equation I). 

The McMurry reaction involving low-valent titanium species accomplishes coupling of two carbonyl groups to furnish aUcenes. The low-valent titanium species is generated either from TiCls/LAH , TiCls/Mg or TiCU/Zn-Cu. When one or both carbonyl substrates carry one or more additional double bonds, dienes or polyenes result from this reaction (equation 109) . The McMurry coupling reaction is remarkably selective and a wide variety of functionalities are tolerated. This reaction can be carried out in both inter- and intramolecular modes to furnish a variety of dienes and polyenes. Synthesis of dienes and polyenes where McMurry coupling has been a key reaction is given in Table 21 . 

Table 2 Preparation of Sterically Hindered Alkenes by the McMurry Coupling Reaction...

Poly(ferrocenylene vinylene) derivatives 68 with values of 3,000-10,000 and polydispersities of ca. 2.2-2.8 (determined by GPG) were synthesized in 1995 in high yields via a titanium-induced McMurry coupling reaction of the corresponding alkylferrocenyl carbaldehyde monomers (Equation (26)). " Gharacterization of these soluble polymers by NMR and IR revealed the presence of trans-Yinylcnc units. The UV-VIS spectra of the polymers are similar to those of the monomers and this indicates a fairly localized electronic structure in the former. The relatively limited electron localization is also reflected in the electrical and optical properties. For example, the values for iodine-doped conductivity a= 10 Scm ) and non-linear third-order optical susceptibility (x = 1-4 x 10 esu) are lower than those of linear conjugated polymers such as poly(l,4-phenylene-vinylene) (a = 2.5x 10 Scm" = 8 X 10 esu). 

McMurry coupling of the appropriate ketones gave the alkenes which are converted into amines by treatment with dimethylamine at 60 °C. The McMurry coupling reaction gives a mixture of (Z) and ( )-isomers that can be separated by semipreparative HPLC. 

The /3-phenyl ring of OH-Tam has also been substituted by a ferrocenyl group to give complexes 3a-e, called ferrocifens (see Figure 2). The synthesis of these complexes employs McMurry coupling reactions, similar to... 

Figure 13.7. Mechanism of the McMurry coupling reaction. [Reprinted with permission from McMurry, J.E. Fleming, M.P. Kees, K.L. Krepski, L.R. J. Org. Chem., 1978, 43, 3255. Copyright 1978 American Chemical Society.]...

Alkenes can be obtained from aldehydes or ketones on reductive dimerization by treatment with a reagent prepared from titanium(III) chloride and zinc-copper couple (or L1A1H4), or with a species of active titanium metal formed by reduction of titanium(III) chloride with potassium or lithium metal. This McMurry coupling reaction is of wide application, but in intermolecular reactions generally affords a mixture of the E- and Z-alkenes (2.99). 

A combination of alkali metal salts, particularly potassium chloride, with low-valent titanium reagents generated from titanium chlorides with lithium or magnesium in either THF or DME are effective reagents for stereoselective McMurry coupling reactions of aldehydes and ketones to substituted alkenes (Figure 1.11). 

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). 

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