Allylic alkylations tungsten

As described in many reviews, Trost and his co-workers have carried out a pioneering work on the molybdenum-and tungsten-catalyzed allylic alkylation of allylic esters regioselectivity of the reaction is often complementary to the palladium-catalyzed allylic alkylation. The first asymmetric version was disclosed by Pfaltz and Lloyd-Jones in 1995 (Equation (63)). They used a catalytic amount of a novel tungsten complex, prepared from [W(CO)3(MeCN)3] or [W(cycloheptatriene) (COIs] and optically active (diphenylphosphino)phenyloxazolines 57, for the allylic alkylation of 3-aryl-2-propenyl phosphate with dimethyl sodiomalonate to isolate the corresponding branched alkylated compounds as a major isomer with an excellent enantioselectivity (96% ee). Unexpectedly, 3-aryl-2-propenyl carbonates are shown to be unreactive. It is worth noting that an isostructural molybdenum complex does not promote the catalytic alkylation under the same reaction conditions. In contrast, Lloyd-Jones and Lehmann reported the stereocontrolled... 

Asymmetric allylboration, characteristics, 9, 197 Asymmetric allylic alkylation, allylic alcohols with copper, 11, 99 with iridium, 11, 105 with molybdenum, 11, 109 with nickel, 11, 102 with non-palladium catalysts, 11, 98 with platinum, 11, 103 reaction systems, 11, 112 with rhodium, 11, 104 with ruthenium, 11, 108 with tungsten, 11, 111... 

In 1965, Tsuji et al. observed that palladium could catalyze the allylic alkylation reaction [18]. This discovery, which is a very attractive way to expand the scope of the allylic amination reactions mentioned above, has stimulated an intense research in this field, and even though complexes of nickel, platinum, rhodium, iron, ruthenium, molybdenum, cobalt, and tungsten have been found also to catalyze the alkylation, palladium complexes have received by far the greatest attention [19]. 

The simple metal hexacarbonyls of molybdenum and tungsten will catalyze allylic alkylation, with dramatic effects on the regioselectivity. The comparison of Mo(CO)6 with Pd° shows a remarkable contrast in regioselectivity (equation 67). The basis for the selectivities is somewhat mysterious, especially considering another dramatic reversal of selectivity with change in anion, from malonate, using Mo(CO)6 and the same conditions. This regioselectivity of Mo carbonyl catalysts has been used to synthesize (7 )-baclofen, as shown in equation (68). 

Tungsten carbonyl complexes are also effective catalysts, showing some preference for nucleophile addition at the more hindered position of an unsymmetrical allyl ligand (equations 69 and 70). Other allylic alkylation reactions... 

Keywords Allylic substitution, AUylation, Allylic alkylation, 7i-Allyl complexes. Palladium, Molybdenum, Tungsten, Iridium... 

A Swain-Lupton Correlation for Tungsten-Bipyridine-Catalyzed Allylic Alkylation... 

Lehman, J., and Lloyd-Jones, G. C. "Regiocontrol and Stereoselectivity in Tungsten-Bipyridine Catalyzed Allylic Alkylation." Tetrahedron, 8863-8874 (1995). 

Another synthetically useful reaction is catalytic allylic alkylation (Eq. 12.81). With this reaction, the X group can be a halogen, as well as other commonly available substrates such as acetate or carbamate. The synthetic utility derives mostly from stereochemical control, which is briefly introduced in the Connections highlight below. This reaction is widespread in organometallic chemistry and has been found to be catalyzed by a variety of metals, including nickel, palladium, platinum, rhodium, iron, ruthenium, molybdenum, and tungsten. 

An Example of a Change in Mechanism in a Solvolysis Reaction Studied Using cr" 452 A Swain-Lupton Correlation for Tungsten-Bipyridine-Catalyzed Allylic Alkylation 453 Using Taft Parameters to Understand the Structures of Cobaloximes Vitamin 612 Mimics 455 The Use of the Schleyer Method to Determine the Extent of Nucleophilic Assistance in the Solvolysis of Aryl vinyl Tosylates 459... 

Phosphinocarbenes, with tungsten carbonyls, 5, 678 Phosphino ligands, on Ti(IV) mono-Cp complexes, 4, 393 Phosphinomethanides, with Zr(IV), 4, 789 Phosphinooxazolines, in allylic ester alkylations, 11, 83—86 0-Phosphinophenoxo ligands, on mono-Cp Ti(IV) complexes, 4, 487... 

Addition of an electrophile (see Electrophile) to metal-bound cyanides will often form an isocyanide ligand (see Electrophile), -CsN-R. For example, the compound [Fe P(OMe)3 (NO)2(j7 -C3H4R)], which is a source of the allyl cation ( -C3H4R)+, reacts with trans-[Mn(CN)(CO)(dppm)2] to alkylate the cyanide, giving an allyl isocyanide ligand (equation 8). The tungsten alkyne... 

Tungsten(n) shows much less tendency to M—M multiple bonding. The W2(02CR)4 compounds are much less stable than those of Mo and have not, in fact, been unequivocally shown to be isostructural with them.53 No dinuclear halo complex or allyl derivative of Wn is known. However the Mo111 and W1" alkyls M2(CH2SiMe3)6 are isomorphous and have a short, triple M-—M bond (see page 757) the neopentyls are similar.54... 

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