Titanium Compounds couple

Formation o( oleltns by coupling or cross coupling of ketones, mediated by low valent titanium Also coupling ol enol ethers of 1,3-dicarbonyl compounds. 

Organic titanium compounds, 25 71-158 See also Titanium compounds in adhesives, 25 122 alkoxides, 25 72-86 as catalysts, 25 122 as coupling agents for polymer composites, 25 129-130... 

Titanium compounds are used very frequently in organic synthesis, however, often stoichiometrically [8]. [Cp2TiCl]2 is the most frequently applied titanium reagent to mediate radical reactions (reviews [123, 124]). Radicals are also often invoked in McMurry couplings mediated by low-valent titanium species (reviews [125-127]) and in the related pinacol coupling (reviews [128-130]). 

Dams, R., Malinowski, M., Geise, H. J. Reductive couplings with low-valent titanium compounds (McMurry reaction). An ESR investigation into the TiCl3/LiAIH4/ROH system. Transition Metal Chemistry (Dordrecht, Netherlands) 1982, 7, 37-40. 

Mukaiyama has described a total synthesis of taxol wherein pinacol cyclization of a diketone was employed to construct the A ring in good yield (Eq. 3.13) [31J. In this work, partially reduced alcohols and rearranged compounds were the major side products of the titanium-mediated coupling process. 

Titanium complexes derived from ethylene-bridged 2-indenyl ligands (Scheme 650) have been prepared by reductive dehydroxy coupling of 2-(hydroxymethyl)indenes with low-valent titanium compounds. Alkyl substitution of the indene ring at C(3) improves the regioselectivity of the reductive coupling.1671... 

The McMurry35 uses low-valent titanium to couple two carbonyl groups together and works very well when the two compounds are the same the symmetrical stilbene -174 can be made in 95% yield and in almost perfect (99.92 0.04 E Z) -selectivity from 3-fluorobenzaldehyde 173. The low-valent titanium is produced by reduction of Ti(III) with lithium metal.36... 

Reductive cross-coupling of carbonyl compounds. The low-valent titanium species couples ketones to nitriles and carboxylic acid derivatives such as esters and acid chlorides. The products represent reductive acylation products of ketones. ... 

Several other methods for the synthesis of PPVs have been described in the literature. The McMurry reaction, which consists of the deoxygenative coupling of aromatic dialdehydes in the presence of titanium compounds, has been employed to obtain 2,5-dihexyl-PPVs [69], para- and meta-FFV (20) [70], Scheme 11, the latter very unlikely to be prepared by the Wessling-Zinmerman or electrochemical routes, since there is no possibility of forming the required quinodimethane intermediate. Nevertheless, a drawback of this method is the somewhat tedious workup needed for the isolation of insoluble PPVs from the elementary metal powder (Ti and/or Zn), which is also produced. 

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