Strong base, Grignard reagent

In a formal sense, a Grignard reagent can be thought of as the mag- nesium salt, RaC" MgX, of a hydrocarbon acid, R3C-H. But because hydrocarbons are such weak acids, with pATa s in the range 44-60 (Section 8.8), carbon anions are very strong bases. Grignard reagents therefore react with... 

Alkynyl anions are more stable = 22) than the more saturated alkyl or alkenyl anions (p/Tj = 40-45). They may be obtained directly from terminal acetylenes by treatment with strong base, e.g. sodium amide (pA, of NH 35). Frequently magnesium acetylides are made in proton-metal exchange reactions with more reactive Grignard reagents. Copper and mercury acetylides are formed directly from the corresponding metal acetates and acetylenes under neutral conditions (G.E. Coates, 1977 R.P. Houghton, 1979). 

Organohthmm compounds and Grignard reagents are strong bases and react instantly with compounds that have —OH groups... 

Problem 10.9 l How strong a base would you expect a Grignard reagent to be Look at Table 8.1 on page 271, and then predict whether the following reactions will occur as written. (The pKa of NH3 is 35.)... 

Many other kinds of organometallic compounds can be prepared in a manner similar to that of Grignard reagents. For instance, alkyllithium reagents, RLi, can be prepared by the reaction of an alkyl halide with lithium metal. Alkyllithiums are both nucleophiles and strong bases, and their chemistry is similar in many respects to that of alkylmagnesium halides. 

The simple hexaalkylditins, RsSnSnRs, do not disproportionate on heating, but, in oxolane (tetrahydrofuran) or acetonitrile in the presence of a base such as a Grignard reagent, or in the more strongly basic solvent hexamethylphosphoric triamide (HMPT), disproportionation readily occurs at room temperature, and, in HMPT, addition occurs to such alkynes as phenylacetylene and diphenylbutadiyne. The disproportionation is considered to proceed by nucleophilic attack upon tin (259, 260), e.g.,... 

Imines can be deprotonated at the a-carbon by strong bases to give the nitrogen analogs of enolates. Originally, Grignard reagents were used for deprotonation but lithium amides are now usually employed. These anions, referred to as imine anions... 

MetalIa-/3-diketonate complexes, such as 1, are conveniently prepared by reacting acylmetal carbonyl complexes with strong bases that can also react as nucleophiles, such as organolithium, Grignard, or boron hydride reagents [Eq. (1)]. These reactions can be followed by IR spectroscopy. 

The most important and widely used approach to chiral sulfoxides is the method developed by Andersen (5) based on the reaction between the diastereomerically pure (or strongly enriched in one dia-stereomer) menthyl arenesulfinates and Grignard reagents. The first stereospecific synthesis of optically active (+H7 )-ethyl p-tolyl sulfoxide 22 was accomplished in 1962 by Andersen (75) from (-)-(iS)-menthyl p-toluenesulfmate 45 and ethylmagnesium iodide. 

The carbanion equivalent from a Grignard reagent is also a strong base. pATa values for alkanes are typically about 50, and for aromatics about 44. Not surprisingly, a Grignard reagent reacts readily with... 

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