Allylic rearrangement, palladium catalyse

H. H. Baer and Z. S, Hanna, The preparation of amino sugars and branched-chain sugars by palladium-catalysed allylic substitution of alkyl hex-2-enopyranosides. Can. J. Chem. 59 889 (1981). D. P. Cuiran, An approach to the enantiocontrolled synthesis of pseudomonic acids via a novel mon-Claisen rearrangement. Tetrahedron Lett. 23 4309 (1982). 

The chemistry of allylic alcohols and their derivatives is remarkably rich. They can be used to add allyl groups to other molecules with good regio- and stereochemical control. The methods in this chapter, particularly the palladium-catalysed reactions and the sigmatropic rearrangements, should allow you to make many otherwise difficult target molecules. 

A full account of the palladium-catalysed, highly regioselective rearrangement of 0-allyl phosphorothioates to their S-isomers has appeared (a preliminary announcement appeared in Organophosphorus Chemistry , Vol. 12, p. 101). 

Palladium-Catalysed Allylic Alkylation 4.3.1 Carroll Rearrangement... 

The role of acid-promoted palladium-catalysed isomerization in the skeletal rearrangement of cyclic amines has been reported. A palladium-catalysed tunable functionalization of allylic imidates, including regioselective aminodiacetoxylation and aziridination with switchable reactivity towards divergent C—N and C—O bond formation, has been reported (Scheme 137). ... 

In a total synthesis of ( )-amathaspiramide F, via a tandem palladium-catalysed allylic amination/[2,3]-Stevens rearrangement, the unexpected diastereoselectivity of the [2,31-rearrangement has been reported to be controlled by substitution patterns of the aromatic ring (Scheme 55)7 ... 

A palladium-catalysed decarboxylative allylic rearrangement of IV-alloc indoles has been reported that can also be combined with a Suzuki-Miyaura cross-coupling reaction in a single pot transformation (Scheme 144) ... 

A two-step stereoselective strategy for converting glycine-derived aminoesters into unnatural cyclic amino acids has been reported. The process involves a palladium-catalysed tandem allylic amination/[2,3]-Stevens rearrangement followed by a ruthenium-catalysed ring-closing metathesis (Scheme 175). " ... 

Further examples of the palladium-catalysed l,3-(oxygen-to-carbon) rearrangement in allyl vinyl ethers have been noted. Detailed mechanistic and stereochemical considerations have lead to a clear picture of how these reactions can be used in cyclopentanone synthesis. The reaction nicely complements the normal thermal [3.3]rearrangement of allyl vinyl ethers. 

Alkylidenetetrahydrofurans such as (30) undergo palladium (0)-catalysed rearrangement to cyclopentanones, in contrast to the thermal rearrangement, which leads to cycloheptanones [equation (38)]. Palladium-catalysed alkylation of /3-keto-esters and allylic ethers can be carried out in an intramolecular fashion to synthesize cyclopentanones [equation (39)].The O- to C-rearrangement of intermediates closely related to (30) was also noted in this reaction. 

The reaction of allyl bromides with allyltin reagents, catalysed by palladium or zinc chloride, gives cross-coupled products without allylic transposition in the allyl halide partner, but with predominant allylic rearrangement from the tin partner. Similar unsymmetrical cross-couplings of allylstannanes with allyl acetates have also been observed (Scheme 19). ... 

Substitution reactions of allylic nitro compounds often lead to rearranged products, as in palladium(0)-catalysed aminations and alkylations. Thus treatment of the nitro ester 419 with piperidine in the presence of tetrakis(triphenylphosphine)palladium yields a mixture of the unrearranged and rearranged amines 420 (R = piperidin-l-yl) and 421... 

The asymmetric aza-Claisen rearrangement of allyl imidates, (86) (87), has been shown to be catalysed by homochiral cationic palladium(II) complexes, and a series of enantiopure cyclopalladated ferrocenyl amines and imines have been... 

Dehydrobromination of bromotrifluoropropene affords the more expensive trifluoropropyne [237], which was metallated in situ and trapped with an aldehyde in the TIT group s [238]synthesis of 2,6-dideoxy-6,6,6-trifluorosugars (Eq. 77). Allylic alcohols derived from adducts of this type have been transformed into trifluoromethyl lactones via [3,3] -Claisen rearrangements and subsequent iodolactonisation [239]. Relatively weak bases such as hydroxide anion can be used to perform the dehydrobromination and when the alkyne is generated in the presence of nucleophilic species, addition usually follows. Trifluoromethyl enol ethers were prepared (stereoselectively) in this way (Eq. 78) the key intermediate is presumably a transient vinyl carbanion which protonates before defluorination can occur [240]. Palladium(II)-catalysed alkenylation or aryla-tion then proceeds [241]. 

Despite the similarity between compound 1 and (-)-swainsonine, a different retrosynthetic strategy was devised for the synthesis of (-)-swainsonine (Scheme 3).19 The ring rearrangement yielded the hydropyrrolidine 5, which was prepared from the precursor 6. The enantiometrically pure oxazolidine derivative 7 was a suitable chiral starting material, as it was efficiently synthesised from the diol 8. As with the synthesis of 1, a palladium (0) catalysed allylic amination was carried out in the presence of ligand L (Scheme 2)14 to give 7 with an ee of 97%, which was increased to >99% on recrystallisation with dichloromethane/hexane. 

Asymmetric decarboxylative rearrangement (Carroll rearrangement) of allyl a-acetamido-/3-ketocarboxylates, catalysed by a palladium complex modified with a chiral phosphine ligand, has been reported to give optically active /,5-unsaturated a-amino ketones with up to 90% ee (Scheme 92).135 The mechanism for the Carroll rearrangement is shown in Scheme 93. 

The catalysed rearrangement of allylic imidates including allylic trichloroace-timidates such as (12.12) has been reported by Overman using palladium catalysts with some of the highest ees obtained using the cobalt oxazoline palladacycle (12.13). 

Cobalt Oxazoline Palladacycles (COPs) are organocobalt-palladium complexes which catalyse the asymmetric rearrangements of non-chiral allylic trichloroacetamidates with very high enantiomeric selectivity (>90%) to provide chiral allylic amines [it is an aza-Claisen rearrangement, The Overman Rearrangement Overman Carpenter Org React 66 2005, Kirsch, Overman and Watson J Org Chem 69 8101 2004] and in the presence of phenols stereospecific cross-couphng also occurs to provide chiral phenoxyallyl ethers with veiy high (>90%) enantiomeric selectivity [Kirsch, Overman and White Org Lett 9 911 2007, Overman Carpenter Org React 66 2005]. 

In some cases, the mercury(II)- and palladium(II)-catalysed allylic Overman rearrangement of trichloroacetimidates can be accomplished under mild conditions at room temperature or even much lower temperature. For example, the trichloroacetimidic ester of geraniol 12 is converted to linalyl trichloroacetamide 13 when treated with 0.2 equiv of mercuric trifluoroacetate at room temperature for 10 min. This catalytic... 

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