Grignard reagent allyl displacement

Alkyl, aryl, and allyl derivatives of boron can be prepared directly from the corresponding halides, BF3, and magnesium metal. This process presumably involves in situ generation of a Grignard reagent, which then displaces fluoride from boron.2... 

Nucleophilic attack on ( -alkene)Fp+ cations may be effected by heteroatom nucleophiles including amines, azide ion, cyanate ion (through N), alcohols, and thiols (Scheme 39). Carbon-based nucleophiles, such as the anions of active methylene compounds (malonic esters, /3-keto esters, cyanoac-etate), enamines, cyanide, cuprates, Grignard reagents, and ( l -allyl)Fe(Cp)(CO)2 complexes react similarly. In addition, several hydride sources, most notably NaBHsCN, deliver hydride ion to Fp(jj -alkene)+ complexes. Subjecting complexes of type (79) to Nal or NaBr in acetone, however, does not give nncleophilic attack, but instead results rehably in the displacement of the alkene from the iron residue. Cyclohexanone enolates or silyl enol ethers also may be added, and the iron alkyl complexes thus produced can give Robinson annulation-type products (Scheme 40). Vinyl ether-cationic Fp complexes as the electrophiles are nseful as vinyl cation equivalents. ... 

Mechelke, M.F., and Wiemer, D.F. (1999). Synthesis of farnesol analogues through Cu(I)-mediated displacements of allylic THP ethers by grignard reagents. J Org Chem 64 4821 829. 

When the substrate is a vinylic epoxide, Grignard reagents generally give a mixture of the normal product and the product of allylic rearrangement (152). Butyllithium reacted with a difluoroalkylidene epoxide (F2C=CR epoxide) and Sn2 displacement gave alkylation at the difluoro carbon and opened the... 

Zirconocene dichloride was used as a catalyst for allylic displacement of allyl ethers with Grignard reagents [449]. An asymmetric version of this reaction by the use of a catalytic amount of a chiral zirconocene dichloride was independently reported, and it achieved a nearly complete chirality induction [Eq. (205) 450]. 

Allylic displacements. Ring opening of perhydro-iV-tosyl-2-allyl-l,3-oxazines with Grignard reagents leads to enamine derivatives. Temperature dependence of the double bond configuration is remarkable. Allylic carbamates furnish predominantly fZl-alkenes. ... 

The trimethylsilyloxy group of allylic or benzylic alcohols is readily displaced by nucleophiles (malonate anion, alkyl Grignard reagents, hydride (AlCl3-LiAlHif)).91 This limitation as a protecting group should be noted. 

Formation and equilibration of allylic metal derivatives such as those from the allylic bromides 24 and 25 we have just made. Reaction of the Grignard reagent with C02 gives only 27 but displacement of bromide with cyanide leads to the isomeric acid -28 both in good yield.5... 

Allylic chlorides are generally more useful than allylic alcohols for further synthetic operations since they are subject to SN2 displacements and, particularly, to coupling with Grignard reagents. Thus (2) on coupling with methallyl chloride in THF-HMPT gives the 1,5-diene (3) in high yield. Use of HMPT as solvent is essential for satisfactory yields. 

Allylic phosphates are displaced, showing y-selectivity with respect to allylic Grignard reagents. ... 

Ketones. The reagent (1) is a propenoyl anion synthon. After alkylation, enones are released. On the other hand, the adducts undergo allylic displacement with Grignard reagents, and on hydrolytic workup, ketones are formed. The possibility of creating a-bromoalkyl ketones, 1,4-diketones, 2-ethoxy-2-cyclopentenones, and a-keto enamines bespeaks for the versatility of this synthesis. 

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