Chemoselectivity organometallic compound

To make as much carboxylic acid derivative as possible available to the nucleophile at all stages of the reaction, the nucleophile is added dropwise to the carboxylic acid derivative and not the other way around. In Figure 6.41, the approach to chemoselective acylations of hydride donors and organometallic compounds, which we have just described, is labeled as strategy 2 and compared to two other strategies, which we will discuss in a moment. 

Fig. 6.44. Chemoselective acylation of an organometallic compound C with the Weinreb amide D of Figure 6.21 a general approach to ketones.

Fig. 6.47. Top three reactions chemoselective acylations of weakly nucleophilic organometallic compounds with carboxylic acid chlorides.

The SN reaction under consideration is not terminated until water, a dilute acid, or a dilute base is added to the crude reaction mixture. The tetrahedral intermediate B is then protonated to give the compound E. Through an El elimination it liberates the carbonyl compound C (cf. discussion of Figure 6.4). Fortunately, at this point in time no overreaction of this aldehyde with the nucleophile can take place because the nucleophile has been destroyed during the aqueous workup by protonation or hydrolysis. In Figure 6.32 this process for chemoselective acylation of hydride donors, organometallic compounds, and heteroatom-stabilized carbanions has been included as strategy 1. ... 

A simUar chemoselectivity is observed with alkylmanganese compounds prepared from alkyl-lithiums or -magnesiums and Mnl2. The organometallic compounds react with aldehydes at -SO C, wMle ketone addition occurs only at higher temperatures (Scheme... 

Monoalkynyltitanium derivatives TiCl(C=CR)(OPr1)2 are prepared from the in situ formation of Ti(n) species and subsequent reaction with haloalkynes through an addition-/3-elimination mechanistic process, showing that this is a powerful method for the synthesis of organometallic compounds. Investigations are carried out in order to rule out the classical oxidative addition of the low-valent titanium species into the carbon-chloro bond. These complexes can further react chemoselectively with a wide range of functionalized electrophiles.21... 

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