Grignard reagents reaction with allylic epoxides

Allylic halides couple effectively with vinyltin reagents to provide the corresponding 1,4-dienes in high yields.2 Like nickel- and palladium-catalyzed Grignard reactions with allylic ethers, this reaction also proceeds with net inversion of configuration at the allylic center. Similarly, vinyl epoxides react... 

Linstrumelle, G. Lome, R. Dang, H. P. Cu-Catalysed reactions of allylic Grignard reagents with epoxides. Tetrahedron Lett. 1978, 4069-4072. 

Addition of 10% Cul to the reaction of allylic Grignard reagents with epoxides exerts a marked efiect on the regioselectivity. The catalyst also increases the rate of reaction. The a-products are also the main products when sufficient Cul is added to form the stoichiometric dialkyl cuprate of the Grignard reagent, but yields are lower than in the copper-catalyzed reaction. ... 

The Sn2 reaction between a Grignard reagent and an epoxide works reasonably well when the epoxide is ethylene oxide. However, when the epoxide is substituted with groups that provide steric hindrance, a competing reaction can dominate, in which an allylic alcohol is produced. Propose a mechanism for this transformation and use the principles discussed in Section 8.13 to justify why the allylic alcohol would be the major product in this case below. 

For asymmetric synthesis, we had to prepare the enantiomerically pure allene 55 with the proper relative stereochemistry. The allene moiety could be synthesized from epoxy propargyhc derivative 56 through SN2 -type reaction with a Grignard reagent. The epoxy propargylic substrate would be synthesized from allylic alcohol 57 via Sharpless epoxidation for introducing the appropriate stereochemistry of the protected allenyl alcohol. For the stereoselective synthesis of 56, the allylic alcohol 57 would be prepared enantioselectively (Scheme 16). 

The reactions of unsymmetrical allylic Grignard reagents such as (42) with epoxides have recently been studied. The products are 5,e-unsaturated alcohols, and normally the reaction occurs at the internal (y-) carbon of the allyl system to give (43) (Scheme 25), but the addition of Cu iodide reverses this regioselectivity to give the a-product (44). 

Nicolaou et al. used the same sulfonate ester system to prove the compatibility of sulfonate esters with carbon-carbon bond-forming reactions [305]. Functionalization and a simultaneous cleavage procedure have been applied successfully by the use of Grignard reagents 585, the Nagata reagent 583 and stannane as well as lithium organic compounds (579, 581). All compounds namely a-allyl ketone 580, epoxide 582, a-cyano ketone 584 and carbinol 586 could be isolated in 65-85% yield (Scheme 85). 

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