Allylic rearrangement/coupling

Perfluoroalkylzinc iodides, prepared in situ from iodides and ultrasonically dispersed Zn, are coupled with allylic halides via an allylic rearrangement[271]. The Pd-catalyzed homocoupling of allylic acetate in the presence of Zn to give a mixture of regioisomers 416 and 417 may proceed via in situ formation of allylzinc species[272,273]. 

LiAlH4. When the substrate is an allylic alcohol, the reaction is not regiospecilic, but a mixture of normal coupling and allylically rearranged products is found. A free-radical mechanism is involved. The TiCla—LiAlUj reagent can also convert... 

Lithium dialkylcopper reagents couple with allylic acetates to give normal coupling products or those resulting from allylic rearrangement, depending on the... 

Organocopper compounds couple readily with allyl halides under mild conditions. In some instances the reactions are reported to be vigorous. Coupling of ethynylcopper compounds with allyl halides can be effected at the ambient temperature in the presence of halide or cyanide ligands 221). Isolation of some rearranged coupling products in certain reactions 44, 66) may indicate the intermediacy of allylcopper(III) species. The reactions are summarized in Table VII. 

When dialkylcopperzinc reagents R2CuZnCl couple with allylic halides, almost complete allylic rearrangement occurs (Sn2 )> and the reaction is diastereoselective if the allylic halide contains a 8 alkoxy group. Another type of copper reagent... 

The reaction gives good yields with primary, secondary, and tertiary alcohols, and with alkyl and arylhthium reagents. Allylic alcohols also couple with certain Grignard reagents in the presence of a nickel complex to give both normal products and the products of allylic rearrangement. 

Vinylation of heteroaryl triflates also possible. Vinyl halides can be coupled to alkenes to form dienes. " The reaction of dihydrofurans with vinyl triilates and a palladium catalyst leads to a nonconjugated diene, 33. This example illustrates that the product is formed by an elimination step, as with the Heck reaction (13-10), and double bond migration can occur resulting in allylic rearrangement. 

A novel approach to the elaboration of the C12-C13 trisubstituted olefin portion of epothilone D was developed by R.E. Taylor et al. " The authors used sequential NHK coupling and a thionyl chloride induced allylic rearrangement followed by the reductive removal of the chiral auxiliary. 

The formation of allylic rearrangement products from substituted allylic esters suggests the likelihood of an S l mechanism, with S 2 possibly competing lor primary ally lie esieis. Homo-coupling product in the reaction of 31 may result Iron)... 

---