Oxygen nucleophiles allylation

Although transition metal-catalyzed allylic alkylation has become one of the most powerful methods in chemical synthesis, the formation of ether bonds using this process has been slow to evolve.119-121 The main reasons for this disparity are the lower nucleophilicity and higher basicity of oxygen nucleophiles, particularly those derived from aliphatic alcohols, compared to their carbon or nitrogen analogs. However, this notion has rapidly been revised, as recent advances in the O-allylation area have largely addressed the issue of the reactivity mismatch between the hard alkoxide and the soft 7r-allylmetal species to provide a considerable body of literature. 

Rhodium catalysts have also been used with increasing frequency for the allylic etherification of aliphatic alcohols. The chiral 7r-allylrhodium complexes generated from asymmetric ring-opening (ARO) reactions have been shown to react with both aromatic and aliphatic alcohols (Equation (46)).185-188 Mechanistic studies have shown that the reaction proceeds by an oxidative addition of Rh(i) into the oxabicyclic alkene system with retention of configuration, as directed by coordination of the oxygen atom, and subsequent SN2 addition of the oxygen nucleophile. 

A wide range of carbon, nitrogen, and oxygen nucleophiles react with allylic esters in the presence of iridium catalysts to form branched allylic substitution products. The bulk of the recent literature on iridium-catalyzed allylic substitution has focused on catalysts derived from [Ir(COD)Cl]2 and phosphoramidite ligands. These complexes catalyze the formation of enantiomerically enriched allylic amines, allylic ethers, and (3-branched y-8 unsaturated carbonyl compounds. The latest generation and most commonly used of these catalysts (Scheme 1) consists of a cyclometalated iridium-phosphoramidite core chelated by 1,5-cyclooctadiene. A fifth coordination site is occupied in catalyst precursors by an additional -phosphoramidite or ethylene. The phosphoramidite that is used to generate the metalacyclic core typically contains one BlNOLate and one bis-arylethylamino group on phosphorus. 

Several types of intramolecular allylic substitution reactions of carbon, nitrogen, and oxygen nucleophiles catalyzed by metalacyclic iridium phosphoramidite complexes have been reported. Intramolecular allylic substitution is much faster than the competing intermolecular process when conducted in the presence of iridium catalysts. Thus, conditions involving high dilution are not required. Intramolecular... 

Palladium-Catal /zed Allylic Alkylation of Sulfur and Oxygen Nucleophiles... 

Palhdium-CatalYzed Allylic Alkylation of Sulfur and Oxygen Nucleophiles 235 Table 2.1.4.14 Pd(0)/BPA-catalyzed asymmetric synthesis of allylic thioesters. 

The HDO and isomerization reactions were previously described as bimolecular nucleophilic substitutions with allylic migrations-the so-called SN2 mechanism (7). The first common step is the fixation of the hydride on the carbon sp of the substrate. The loss of the hydroxyl group of the alcohols could not be a simple dehydration -a preliminar elimination reaction- as the 3-butene-l-ol leads to neither isomerization nor hydrodehydroxyl at ion (6). The results observed with vinylic ethers confirm that only allylic oxygenated compounds are able to undergo easily isomerization and HDO reactions. Moreover, we can note that furan tetrahydro and furan do not react at all even at high temperature (200 C). 

The most intense interest in the addition of oxygen nucleophiles to Tr-allylpalladium complexes has centered on the delivery of OAc. For example, in allylpalladium-OAc complexes, acetate can be induced to migrate to the allyl ligand by the addition of CO (equation 46).162-164 Rearrangements and isomerizations of allyl acetates can also be readily accomplished via Pd catalysis (equations 47 and... 

Amine nucleophiles appear generally to add by attack at the allyl ligand. Similar to oxygen nucleophiles, however, a caveat must be noted in evaluating the observed regioselectivities in that the allyl amine products are capable of rearrangement by reentry into the ir-allyl manifold. 

Dienes (allenes) are also used for heteroannulation with 68 and 69. The eight-membered nitrogen heterocycle 78 is constructed by the reaction of 1,2-undecadiene (77) with o-(3-aminopropyl)iodobenzene (76) [34]. The lactones are prepared by trapping the 7i-allyl intermediates with carboxylic acids as an oxygen nucleophile. The unsaturted lactone 81 is prepared by the reaction of /1-bromo-v,/ -unsaturated carboxylic acid 79 with the allene 80 [35]. In the carboannulation of 82 with 1,4-cyclohexadiene (83), the 1,3-diene 85 is generated by / -elimination of 84, and the addition of H-PdX forms the 7i-allylpalladium 86, which attacks the malonate to give 87 [36],... 

However, reactions of 160 and 161 with methyl 2,2-bisdeuterioacetoacetate (164) give the products deuterated at different carbons namely 2-deuterio-3-hydrofuran 166 is obtained from 160 via 165. Also, reaction of 161 with 164 affords the furan 168, deuterated at the exomethylene carbon via 167. These results are explained by assuming that the attack by the oxygen nucleophile (O-allylation) occurs at the more substituted side of 7c-allylpalladium systems in 165 and 167. 

Oxygen nucleophiles, especially alcohols (and an acid) also reacted with the system allylsilane-IOB.BF3. The allylation of several alcohols (in large excess, often serving as solvents) afforded their allyl ethers in good yields [16] ... 

Acemoglu L, Williams JMJ (2002) Synthetic Scope of the Tsuji-Trost Reaction with Allylic Halides, Carboxylates, Ethers, and Related Oxygen Nucleophiles as Starting Compounds. In Negishi E, de Meijere A (eds) Handbook of Organopalladium Chemistry for Organic Synthesis. Wiley, New York, p 1689... 

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