Grignard reagents reaction with allylic ethers

Reactions of Grignard Reagents with Allylic Esters and Ethers... 

Allylic halides may be readily converted into ethers by reaction with alkoxide ion in refluxing DMF. In the case of a bis-haloallyl compound, a reasonable yield of mono alkoxy-lated product may be formed in some instances (equation 30)246. The product may then be further elaborated by formation of a Grignard reagent at the remaining halogen atom. 

Alkylation of allylic ethers. PdCljCdppf) is the most effective catalyst for alkylation of allyl trialkylsilyl ethers with Grignard reagents to give an internal alkene. NiChfdppf) also catalyzes this reaction, but with the opposite cgioselectivity, thus forming a terminal alkene. 

The same year, it was noted by Commer on [54] that the use of the Cu Br catalysis for the reaction of Grignard reagents with allyl methyl ethers lead to the mixture of Sn2 and Sn2 products, according to the steric hindrance of the substrate and the geometry of the double bond [Eq. (37] and Table 6]. 

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]. 

A similar cyclization reaction proceeded on treatment of 2-haloethanal allyl acetal and allyl 2-halophenyl ether with Grignard reagents in the presence of an Fe(II) salt catalyst [177]. Addition of phenylmagnesium bromide to a solution of 2-iodoethanal prenyl acetal 176a in the presence of a catalytic amount of Fe(ll)Cl2 gave the isopropenyl-substituted tetrahydrofuran derivative 177 in 52% yield with an isopropyl-substituted product 180 (13%) (Scheme 3.164). 

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]. 

Reaction with allylic ethers. Alkenes are obtained by reaction of allylic ethers with Grignard reagents catalyzed by cuprous chloride or bromide. Direct replacement of the ether group takes place as the major reaction when the ether is primary. Secondary and tertiary allylic ethers react mainly with rearrangement. 

The synthesis of allylic ethers from alkenes via electrochemical oxyselenenyla-tion has been mentioned earlier in this Report (Scheme 13). Details have appeared of the reaction of acetals of a,/3-unsaturated aliphatic aldehydes with Grignard reagents in the presence of TiCU to give allylic ethers in high yields [equation (12)] ° it was also found that the 2,4-dichlorophenoxy-group could... 

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