Grignard allylic substitution

Allylic substitution reactions [1] will be discussed in the 8 2 versus 8 2 (see Chapter 24) cyclization reactions from di-Grignard reagents will be discussed in Chapter 25 metal-catalyzed reactions will be covered in Chapters 29 and 30 the chemistry of acetylenes and Si are covered in Chapters 31 and 32 and while some asymmetric reactions will be discussed, the reader is encouraged to peruse through Chapter 28. 

Enantioselective allylic substitution with Grignard reagents was carried out by chiral nickel complexes to show a maximum e.e. value as high as 94% [241]. Equations (112) [240] and (113) [242,243] illustrate examples. 

Nickel catalysts also catalyze Grignard substitution to allylic compounds including allyl alcohol [230-233] ethers [230,231,234,235 Eq. (106) 231] amines, albeit in a low product yield [231] sulfides [231,236,237], including thioacetals [238] thiols [231] selenides [239] carboxylates [240] phosphates [94,121] and halides [Eq. (107) 230], most likely via intermediate / -allyl-Ni species. Monosubstitution of bis-allyl ether was possible [Eq. (108) 235]. Most of the literatures cited in the foregoing disclosed regiochemical outcome associated with these allylic substitutions. 

Allylic ethers and alcohols have long been known to react with Grignard reagents in the presence of an appropriate Ni-based complex containing phosphine ligands [26]. These reactions are related to the well-studied Pd-catalyzed allylic substitution reactions that utilize soft nucleophiles [27], and a number of important mechanistic studies on the stereochemical outcome of this class of transformations have been carried out [28]. 

The scope of the method turned out to be particularly broad (Table 12). The allylic substitution of cinnamyl bromide could also be performed with other linear alkyl Grignard 

Metals other than palladium and molybdenum can be used for allylic substitution reactions. For example, nickel in the presence of the oxazolinylferrocenylphosphine 9 provides good asymmetric induction for the reaction of a Grignard reagent with allylic electrophilic systems such as acetates.151 

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