Reactions with organometallic compounds chemoselectivity

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. ... 

Far milder reaction conditions are possible if a transmetalladon of the zinc organometallic (21) to the mixed copper-zinc derivative (22) is first performed and if the reaction is carried out in the presence of 2 equiv. of BFa-OEtj. A wide range of functional groups are tolerated in compounds (21) and (22), and high yields are usually obtained (68-93% see Scheme 8), the reaction showing a good chemoselectivity. The treatment of a 1 1 mixture of boizaldehyde and acetophenone with the organozinc iodide (23 2 h at... 

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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