McMurry reagent reductive

The McMurry reagent reductively couples trifluoroacetophenones to the eorresponding stilbenes [67] (equation 55), and cross-coupling of ketones is also reported [68] (equation 56). 

Another well-known transformation of carbonyl derivatives is their conversion to pinacols (1,2-diols) via an initial one-electron reduction with highly active metals (such as sodium, magnesium, aluminum, samarium iodide, cerium(III)/ I2, yttrium, low-valent titanium reagents (McMurry coupling), etc.), amines, and electron-rich olefins and aromatics as one-electron donors (D).43 Ketyl formation is rapidly followed by dimerization44 (equation 22). 

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>. 

Crucially, it was found22 that upon reaction of the vinylketene complex 42.a with 1-pentyne, the same product distribution was seen as for the direct thermolysis of 1-pentyne with the precursor carbene 43.a. The analysis was simplified by reduction of the crude reaction mixture with McMurry s reagent to produce a mixture of the isomeric indanols 44-46. 

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. 

Another possibility for creating a new ligand structure is to connect two phos-phaferrocene molecules via their formyl functional groups. The reductive coupling of carbonyl compounds with low-valent Ti reagents - the McMurry reaction - is a technique that has found wide application in organic synthesis [18]. 

Wynberg studied stereochemistry of the McMurry reductive dimerization of camphor in detail (64). In Scheme 37, A and B are homochiral dimerization products derived by the low-valence Ti-promoted reduction, while C and D are achiral heterochiral dimers. The reaction of racemic camphor prefers homochiral dimerization (total 64.9%) over the diastereomeric heterochiral coupling (total 35.1 %). Similarly, as illustrated in Scheme 38, oxidative dimerization of the chiral phenol A can afford the chiral dimers B and C (and the enantiomers) or the meso dimer D. In fact, a significant difference is seen in diastereoselectivity between the enaritiomerically pure and racemic phenol as starting materials. The enantiomerically pure S substrate produces (S,S)-B exclusively, while the dimerization of the racemic substrate is not stereoselective. In the latter case, some indirect enantiomer effect assists the production of C, which is absent in the former reaction. Thus, it appears that, even though the reagents and reaction conditions are identical, the chirality of the substrate profoundly affects the stability of the transition state. 

McMurry developed a reduction procedure that is used for alkenation of carbonyl compounds in the presence of low-valent titanium (LVT) reagent. The reagent (thought to be a mixture of Ti(0) and Ti(II) species) is formed by the reduction of TiCU or TiCb with a suitable reducing agent (Zn-Cu alloy, LiAlH4 or alkali metal are the most commonly used). 

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 most widely used systems are those employing low-valent titanium species. The reductive coupling of carbonyl compounds by titanium reagents was independently discovered in 1973 by Trylik and Mukaiyama, and has since been extensively developed by McMurry and his coworkers." " The McMurry reaction, as it has become known, has proved to be a valuable synthetic tool for the construction of C=C bonds. 

The reductive coupling of two carbonyl compounds using reduced Ti reagents is called McMurry coupling. The products may be 1,2-diols or alkenes. 

Transient Ti11 complexes have been inferred as reagents in a variety of organic transformations.903 1006-1010 For example, the reactive species (TiH(Cl)(THF) 0.5)x was generated by the reduction of TiCl3(THF)3 with MgH2 and shown to be the active species in the McMurry reaction.1010-1013... 

The reduction of TiCls with 4 eq. of LiAlH4 in THF gives a fine black suspension of a titanium(II) species. A 4 1 ball-milled mixture of TiCls and L1A1H4 is available from Alfa Inorganics ( McMurry s Reagent )- Addition of this stable solid to THF leads to evolution of hydrogen and formation of titanium(II). 

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