Allylic displacement reactions

Fluoride-induced rearrangements of terminal to internal isomers of perfluoro-alkenes are well established [70-72], for example the rapid isomerisation of perfluoro-l-pentene to the thermodynamically more stable isomer occurs in the presence of cesium fluoride (Scheme 33) [73], Allylic displacement reactions occur readily and with a stereochemistry suggesting steric control (Scheme 34) [74],... 

Allylic displacements. Palladium-catalyzed allylic displacement reactions have been carried out in ionic liquids at room temperature. 

Acetate ion is also a competent nucleophile for displacement of hydroxyl groups under Mitsunobu-type (Appel) reaction conditions (eq 13), and has been used in palladium-catalyzed allylic displacement reactions (eq 14)T ... 

Azide salts are a class of versatile nitrogen nucleophiles that can be readily employed as reaction partners in palladium-catalyzed allylic displacement reactions. A telling example was documented by Trost in the desymmetrization of bis-carbonate 51 to give azide 52 in an excellent 95% ee (Scheme 14.10) [66]. The fact that the reaction proceeds under mild conditions ensures that any undesired rearrangement of the allylic azide 52 is suppressed. 

Phenols have been documented to serve as a versatile class of 0-nucleophiles in asymmetric allylic alkylation events. Even a sterically hindered ortho-disubstituted phenol such as 59 participated in a palladium-catalyzed allylic displacement reaction with carbonate 60 (Scheme 14.12) [69]. Product 62 was obtained in 88% ee and subsequently converted into (-)-galantha-mine (63), a selective inhibitor of acetylcholinesterase with potential in the treatment of Alzheimer s disease [69, 70). 

Carreira has reported a conceptually different class of chiral ligands for iridium-catalyzed allylic displacement reactions (Equation 6) [87]. The use of chiral diene 89 in combination with Ir(I) led to kinetic resolution of racemic allylic carbonates. The resulting allylic ethers (cf 90) and recovered starting allylic carbonates are obtained with high enantioselectivity. The modular chiral diene ligands, exemplified by 89, are readily available by a short synthetic sequence starting from carvone. 

Ring-opening reactions of unsaturated heterocycles represent a promising alternative to the allylation reactions described in previous sections. In many instances the products that can be isolated from such transformations are not otherwise readily accessible [38, 40, 41]. These transformations share mechanistic similarities with carbometalation of olefins (Section 13.6). Because the products are formally derived from allylic displacement reactions, however, they are included in the current chapter. 

For our definition of the term a position , see [6]. There is an older usage of the terms a and y in the discussion of palladium-catalyzed allylic displacement reactions, where... 

An extensive study (6) of Sn displacement reactions of allyl halides using silyl anions/anionoids has provided the following regioselective alternatives ... 

TABLE 2. Product distribution for the displacement reaction of allyl sulfones 9 with lithium dialkyl cuprates6... 

It is interesting that when EtOe, in fairly high concentration, is used as the nucleophile in preference to EtOH, the reaction of (19) becomes SN2 in type and yields only the one ether (21). Allylic rearrangements have been observed, however, in the course of displacement reactions that are proceeding by a bimolecular process. Such reactions are referred to as SN2 and are believed to proceed ... 

Substitution of fi-nitro sulfides.2 (3-Nitro sulfides in the presence of a Lewis acid undergo displacement reactions with either allyl- or cyanotrimethylsilane. The reaction is considered to involve an episulfonium intermediate, which is then substituted at the more positive carbon (equation I). The reaction proceeds with retention of configuration, and anti (J-nitro sulfides react much more rapidly than... 

The limited extent of intramolecular rearrangements undergone by the chiral oxonium ions 35 and 36 at 720 torr and at 40 °C (Table 22) allows their use for probing the regio- and stereochemistry of the displacement reactions of Scheme 19. In this case, the allylic alcohol, precursor of the chiral oxonium ions 35 and 36, acts as the nucleophile NuH. The relevant results are condensed in Scheme 21. 

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