Aldehydes McMurry coupling

R2 = Et) have been prepared15 by McMurry coupling of the corresponding tetrapyrroledicarb-aldehydes and subsequent oxidation of the dihydro intermediates which were, as in the por-phycene series, initially formed. 

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... 

Scheme 1.5.7 McMurry-coupling of aldehyde 2 yielding olefinic products.

Condensation of the allyl silane 4 with 3 proceeded to give exclusively the desired trans dihydropyran 5. McMurry coupling of the derived keto aldehyde gave the diol 13 as a mixture of diastereomers. Oxidation of the mixture gave 2 and its C-8 diastereomer in a ratio of 8 1. 

Porphycenes with fused aromatic rings between 3,6 and 13,16 positions of 61 (Scheme 29) have been prepared through McMurry coupling of aldehyde 60, followed by DDQ oxidation of the nonaromatic N,N -dihydroporphycene intermediate (05ACI4053,1993PAC143). 

To date, only the simplest member of the oligo(phospholylenevinylidene) family, namely derivative 62 (Scheme 4.17), is known [47b]. This compound can be obtained in high yield, as the E-isomer, by a McMurry coupling with aldehyde 61 (Scheme 4.17) [47b]. Note that the use of Ti salts is compatible with the presence of g3-P centers. No photophysical data for the orange mixed phosphole-ethenyl derivative 62 have been reported. 

Stereoselective McMurry coupling. Clive and co-workers1 report that a modified McMurry reagent prepared in DME with C8K and TiCl3 ( 2 1) can effect highly stereoselective coupling of keto aldehydes. Thus the key step in a synthesis... 

McMurry coupling, Tebbe reagent, Petasis reagent and Takeda reagent) and catalytic alke-nation of aldehydes and ketones plus the related reactions in each case. 

Stuhr-Hansen has reported on a microwave-induced high yielding synthesis of alkenes by McMurry coupling of aldehydes and ketones. With microwave heating, the corresponding alkenes have been produced much faster with higher yields (>80%) as compared to conventional heating. 

The McMurry coupling is most useful for the intramolecular reduction of aldehydes and ketones to form cycloalkenes with ring size varying from 3 to 36. The medium and large rings are usually formed with the -configuration . 

In the laboratory of T. Nakai, the asymmetric tandem Claisen-rearrangement-ene reaction sequence followed by a modified McMurry coupling was used to access (+)-9(11)-dehydroestrone methyl ether. The Claisen-ene product was subjected to ozonolysis and epimerization to the 8,14-anf/ configuration. The C-ring was constructed by treating the tricyclic diketo aldehyde with TiCl3-Zn(Ag) in DME to afford the desired final product in 56% yield. 

A one-pot synthesis of phenanthrenes from ortho-alkoxy a re ne aldehydes and ketones has been accomplished using TiCl3-Li-THF [103]. The 2,2 dialkoxystil-benes, resulting from a classical McMurry coupling [80], are subjected to a reductive dealkoxylation and under the reaction conditions applied [103] form the intramolecular CC coupling products in moderate overall yields (25-38%). 

The method for conversion of benzylic bromide to aldehyde with IBX and DMSO has been applied to a molecule containing six such structural units, to deliver a precursor of the belt-shaped [6.8]3cyclacene by a threefold intramolecular McMurry coupling. ... 

An ingenious approach to racemic estrone has used two reactions in a combined tandem Cope-Claisen rearrangement (ref. 130). 1-Bromomethyi-3,4-dihydro-6-methoxynaphthalene is used to alkylate 1-methoxycarbonyl-2-methylcyclopent-2-ene and the ester group in the product converted to a vinyloxymethyl substituent. Thermolysis afforded a mixture of diastereoisomeric aldehydes (2 1) containing a majority of the trans compound. Ozonolysis and epimerisation at the 8-position succeeded by McMurry coupling gave the required tetracyclic structure from which racemic estrone methyl ether was obtained. 

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). 

McMurry coupling of aldehydes and ketones for the formation of heter-ocyles via olefination 12COC2097. 

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). 

Pinacolization sometimes occurs when undesired, but it is difficult or unsatisfactory when needed. A few attempts to improve this reaction by sonication (Fig. 18) have met with limited success, and a general solution to this problem remains to be found. Aromatic aldehydes and ketones pinacolize when sonicated with low-valent titanium in DME.57 The reaction is highly sensitive to the nature of the solvent. In apolar media, the reduction of titanium trichloride does not occur, and in THF, the McMurry coupling to olefinsHO is preferred. 

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