Grignard reagent, constitution

The reactions of Grignard reagents constitute an enormously important type of synthetic chemistry, and they can be used in a wide variety of cases. 

The use of a chiral alcohol to prepare diastereomeric alkoxystannanes from racemic triorganostannyl halides, then displacement with a Grignard reagent, constitutes a general route to nonracemic tetraorganostannanes. Chinconine has proven particularly effective as the chiral alcohol (equation 7)19. 

Compounds such as R2SnCl2 and R2SiCl2 have several uses because two reactive Sn-Cl bonds remain that can undergo hydrolysis, reactions with alcohols, and so on. The reactions of Grignard reagents constitute one of the most general synthetic procedures, and they can be used in a wide variety of cases. 

The reaction of germanium(II) iodide with conjugated dienes and the following treatment with Grignard reagents constitutes the convenient method for the preparation of cyclic tetraorganogermanes (eq (95)) [92]. 

Grignard reagents, constitution and mechanism of their reactions with ketones E. C. Ashby, Quart. Rev. 21, 1967, 259... 

Since aluminium alkyls are easily available from inexpensive starting materials, their addition to carbonyl compounds could constitute a cheap alternative to the more expensive Grignard reagents or alkyllithium compounds. Unfortunately, this addition is only clean for aluminium alkyls without /1-hydrogens [16, 19], which are precisely those not accessible via the convenient... 

With these proposals a debate started about the constitution of Grignard reagents in solution which lasted for about sixty years. This topic has been reviewed by Ashby . 

As for additions of allylic Grignard reagents, the relative reactivity order of the olefins appears to be 1-alkenes < styrene < 1,3-butadiene < ethylene and a,oi-or a,/3-disubstituted alkenes do not react94. However, strained alkenes such as cyclopropenes constitute an exception. Indeed, dicrotylzinc smoothly reacted with 3,3-dimethylcyclopropene and afforded the dicyclopropylzinc reagent 130 resulting from a syn addition process (equation 62)93. 

The symbol RMgX will be used to indicate the Grignard reagent, although the constitution of this reagent is more correctly described by equations (8) and (11). 

Grignard reagents derived from aryl bromides are readily prepared and may be converted into organocadmium compounds by treatment with cadmium chloride (cf. Section 5.8.4, p. 616). Reaction of an organocadmium with a carboxylic acid chloride constitutes a convenient synthesis of aryl alkyl ketones. 

Grignard reagents also add diastereoselectively to oc-chiral, oc-oxygenated aldehydes and ketones. The chelation-controlled product constitutes the major product (Figure 10.41). It is the diastereomer that is produced via the Cram chelate transition state of Figure 10.16... 

The basis for assuming that III should react metathetically with a Grignard reagent was that it is a hemiacetal chloride, and the simple chlorides of this type, namely, the a-chloro ethers, are known to react in the manner of Equation (5). This type of. reaction has been used50 for the synthesis of a-substituted ethers, and also constitutes one of the... 

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