Coupling with Grignards

Nickel (II) Catalyzed Cross-Coupling with Grignard Reagents (Kumada Reaction) Pure AppJ. Chem. 1980, 52, 669 Bull Chern. Soc.Jpn. 1976, 49, 1958... 

Allylic amines. The stabase adduct (1) of 2-chloroallylamine couples with Grignard reagents in the presence of NiCl2(dppp), dppp = (CfiH )2P(CH2),P(C6H5)2, to form, after deprotection, allylic amines. 

Trisubstituted alkenes.9 A stereoselective synthesis of trisubstituted alkenes uses (E)-alkenyl sulfoxides (1)>U as the starting material. These are reduced to the corresponding sulfides (2)," which undergo coupling with Grignard reagents in the presence of complexes of nickel chloride and phosphines as catalyst.12 The products (3) are obtained in steroisomeric purity of > 99%. 

Aryl mesylates are used for the Ni-catalysed cross-coupling with Grignard, organozinc and organoboron reagents [100]. 

All of the alkenylations and arylations discussed in this section follow the common mechanism exemplified in Figure 16.18. The steps shown in Figure 16.18 may involve more than one elementary reaction, as in the case of the mechanistic course of the Ni-catalyzed C,C coupling with Grignard compounds (Figure 16.12). It should be noted that the basic sequence of steps is very much the same in Figures 16.18 and 16.12. 

Answer The CH2 =CH-CHa - group is (he ally group. Ailyl halides couple with Grignard reagents very readily as shown below ... 

The enhanced reactivity of allylic halides and tosylates makes them particularly attractive as electrophiles for Sn2 reactions. Allylic halides are so reactive that they couple with Grignard and organolithium reagents, a reaction that does not work well with unactivated halides. 

Activation of allylic and propargylic alcohols. These alcohols can couple with Grignard reagents in the presence of an a-chloroenamine. For this purpose the related reagent l-chloro-2-methyl-N,N-tetramethylenepropenyIamine (2) is more effective than 1. 

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