Grignard compounds stereospecific

Fig. 16.10. Nickel-catalyzed alkenylation of Grignard compounds occurrence of stereoselectivity and stereospecificity.

The order of reactivity of organic halides is I > Br > Cl > F. Although organic iodides are the most reactive, they produce more Wurtz coupling products through the radical oxidative addition process. Thus, it is usually advisable to use the chlorides or bromides, except in the case of aromatic iodides and methyl iodide. 1-Alkenyl Grignard compounds are obtained by the direct reaction of magnesium and vinylic halides in THF [6], but the reaction is not completely stereospecific and the retention of the stereochemistry of haloalkenes varies from 60-90% [7]. The difficulty associated... 

In a method which may only be applicable to the preparation of benzylic carbonyl compounds, Grignard reagents (stereospecifically) transform methyl-sulphinyl derivatives (7) into the anion [equation (6)]. Other than protonation, no further transformations of the arylacetaldehyde derivatives were described. 

In a Kumada-Corriu reaction, an aryl halide is oxidatively coupled with a homogeneous nickel(ll)-phosphine catalyst [2], This species reacts with a Grignard reagent to give biaryl or alkylaryl compounds. Later, palladium-phosphine complexes were also successfully applied. By this means, stereospecific transformations were achieved. 

The stereospecificity of poly(methyl methacrylate) formed after initiation by Grignard or organolithium compounds depends on the solvent, temperature, halogen, and the organic initiator component. A change in any of these factors leads to a substantial change in stereostructure [86, 87]. Also... 

As an additional example, benzoate or phthalate esters are used to modify the solid support and are incorporated into the solid-phase structure. Here, they become effective as internal bases [14], which are critical components in high-stereospecific polypropylene catalysts. As the range of suitable internal bases for stereoregulation increases, these compounds also find their way into reaction schemes involving Grignard reagents. 

Lactones are normally stable compounds, which have found ample application as synthetic intermediates, and, quite recently, have been detected as the central structural unit in physiologically active natural products like obaflorin (123) and lipstatin (124). Characteristic applications of 3-lactones in synthesis are the stereospecific CO2 elimination to form di- and tri-substituted alkenes (e.g. from 125 equation 40) or Grignard addition to the carbonyl group e.g. equation 41). Particularly useful is the formation of 3-lactone enolates (126), which react with a variety of electrophiles (EX) wiA high stereocontrol (equation 42). Organocuprates may be used in chain elongations to form 3-branched carboxylic acids (equation 43). ... 

Requisite diastereomerically enriched menthyl phosphinates may be conveniently obtained by unexceptional methods and examples which constitute the partial realization of this scheme for configurational intercorrelations are shown in Chart II. The absolute configurations of menthyl esters 1 and 2 follow from their correlation with 3, whose chirality at phosphorus is known from X-ray analysis ). The stereochemical direction (inversion) of these highly stereospecific Grignard reactions, and thus the absolute configurations of the derived optically active phosphine oxides, was established by chemical correlations with a second reference compound (4) of known absolute configuration . 

Practicable syntheses of four-, five, and six-membered carbocyclic rings have been achieved by reaction of a,to-di-Grignard reagents with silver(i) salts. Conversion of l,3-bis(chloromethyl)cyclopentane into norbornane was effected in 82% yield, but was the only bridged-ring synthesis reported. Stereospecific cyclic ketone formation using iron(O) compounds has been reviewed. ... 

Vinyl halides react with alkyllithiums with the aid of a palladium(O) complex to give olefins stereospecifically in good yields. When Grignard reagents are employed instead of alkyllithium compounds, these reactions can be carried out catalytically with the palladium complex (Yamamura et al., 1975). or/Ao-Alkylated thiobenzophenones can be similarly prepared from 5-donor ligand or/Ao-metalated complexes (H. Alper and J. Kamenof, unpublished results). 

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