Acetate reactions asymmetric allylation

Reactions with Sulfur Nucleophiles. The use of sulfur nucleophiles in palladium-catalyzed allylic substitution reactions is less well documented than that of carbon, nitrogen and oxygen nucleophiles. The asymmetric synthesis of allylic sulfones utilizing a catalytic phase transfer system has been used to produce (35)-(phenylsulfonyl)cyclohex-l-ene on a 45 g scale (eq 10). In many cases, it has been reported that allylic carbonates are more reactive than allylic acetates in asymmetric allylic substitution... 

Pd-catalyzed asymmetric allylic alkylation is a typical catalytic carbon-carbon bond forming reaction [ 126 -128]. The Pd-complex of the ligand (R)-3b bearing methyl, 2-biphenyl and cyclohexyl groups as the three substituents attached to the P-chirogenic phosphorus atom was found to be in situ an efficient catalyst in the asymmetric allylic alkylation of l-acetoxy-l,3-diphenylprop-2-en (4) with malonate derivatives in the presence of AT,0-bis(trimethylsilyl)acetamide (BSA) and potassium acetate, affording enantioselectivity up to 96% and quantitative... 

Bayardon and Sinou have reported the synthesis of chiral bisoxazolines, which also proved to be active ligands in the asymmetric allylic alkylation of l,3-diphenylprop-2-enyl acetate, as well as cyclopropanation, allylic oxidations and Diels-Alder reactions. [62] The ligands do not have a fluorine content greater than 60 wt% and so are not entirely preferentially soluble in fluorous solvents, which may lead to a significant ligand loss in the reaction system and in fact, all recycling attempts were unsuccessful. However, the catalytic results achieved were comparable with those obtained with their non-fluorous analogues. 

Pfaltz s group also investigated ligand 139 in the reaction involving the asymmetric allylic acetate 141. A substitution ratio (142a/142b) of 93 7 was observed in this case and both products were obtained as pure enantiomers (Fig. 9.43h). 

The asymmetric allylic acetoxylation of cycloalkenes has also been reported. In this case, the catalyst is a bimetallic palladium(II) complex bearing a chiral bisox-azoline or a chiral diphosphine (DIOP). The reaction is performed in acetic acid/ sodium acetate under oxygen atmosphere at room temperature. Under these conditions, acetoxylation products of cyclohexene and cydopentene are obtained with 55 % and 78 % ee, respectively, albeit in low yields [39a]. 

Jt-allyl complex can be generated after cyclization, as suggested by Takacs in a Fe(0)-catalyzed cyclization of polyenes. It also can be preformed if an active functional group is present in the allylic position. The palladium-catalyzed intramolecular cycloisomerization reaction of allylic acetates is an efficient method for constructing five- or six-membered rings [56, 57]. An asymmetric approach to this transformation has been studied and so far only poor enantioselectivity has been achieved (0-20% ee) [58]. Very recently, Zhang et al. also reported a Rh-catalyzed cycloisomerization involving a Jt-allylrhodium intermediate formed from an allylic halide [59]. 

The obtained amino functionalised imidazolium salts could be used to generate the corresponding palladium(ll) carbene complexes using the silver(l) complexes as carbene transfer agents. Application of these palladium(ll) complexes (predominantly in situ) in asymmetric allylic alkylation reactions between ( )-l,3-diphenylprop-3-enyl acetate and dimethyl malonate (a standard reaction for this catalytic process [145]) gave up to 80% ee,... 

Racemic conduritol B acetates and carbonates provide very versatile substrates for asymmetric allylic substitution reactions. Re-... 

The use of C2-symmetric 1,2- and 1,3-diols as chiral auxiliaries is a reliable method for asymmetric allylation of acetals [382]. Acyclic acetals derived from homochiral 1-phenylethanol undergo the Hosomi-Sakurai allylation with high diastereoselectivity [383]. Tietze et al. have, on the other hand, reported that the TMSOTf-catalyzed successive acetalization-allylation reaction of aliphatic aldehydes with homochiral silyl ethers 123 and allyltrimethylsilane gives the corresponding homoallyl ethers with complete diastereocontrol these ethers can be readily converted into enantiomerically pure homoallyl alcohols without epimerization (Scheme 10.135) [384]. This method is applicable to asymmetric allylation of methyl ketones [385]. 

Chiral bisoxazoline associated with palladium is a very efficient organometallic catalyst for the asymmetric allylic alkylation of allylic acetates and carbonates, allowing the formation of carbon-carbon as well as carbon-heteroatom bond in enantiomeric excesses higher than 95%.[1,2] However one of the problems in organometallic homogeneous catalysis is the separation of the catalyst, often toxic and very expensive, from the product(s) of the reaction. Very recently, a chiral fluorous bisoxazoline (Figure 3.1) has been shown to be an efficient ligand in the... 

The degree of asymmetric induction for a substrate bearing a remote chiral auxiliary is discussed in the next example. Palladium(0)-catalyzed asymmetric allylation of (S)-proline allyl ester amides gives the (S.-SJ-diastereomer with d.r. 93 7s7. If the electrophile is not attached to the proline moiety but added as allyl acetate, the diastereoselectivity is only moderate (d.r. 65.5 34.5-74 26 for the methyl or ethyl proline esters). At 0 =C, the reaction does not yield the expected products and at higher temperatures (40 C), only d.r. 82.5 17.5 is obtained. The alkylation with j cr-butyllithium and allyl iodide at — 78 =C gives the epimeric (7 )-enantiomer with d.r. 88.5 11.5. 

In the field of C—C bond forming reactions, palladium occupies a privileged position. In this context, the asymmetric allylic alkylation attracted our interest due to its unique outersphere attack of the malonate on the 77 -coordinated 1,3-diphenylallyl moiety. Following the above-described chemogenetic optimization procedure, we screened twenty one biotinylated ligands in conjunction with twenty two (strept)avidin isoforms for the allylic alkylation of 1,3-diphenylallyl acetate. Addition of didodecyldimethylam-... 

Allylation of simple ketone is not possible under usual conditions, but the reaction can be carried out under selected conditions. Asymmetric allylation of the chiral racemic o -methylcyclohexanone 161 with allyl carbonate proceeded in the presence of LDA as a base with or without MesSnCl as a Lewis acid at room temperature to provide the allylated ketone 162 in very high yield with 82 % ee when (5,5)-Trost L-1 was used. The choice of base is crucial, and it was claimed that no reaction took place when Na or K bases were used in this reaction [57]. Asymmetric allylation of a-aryl and heteroaryl ketones has been carried out. Asymmetric allylation of 2-indolylcyclohexanone 163 took place at 0 C to give the the allyl ketone in 82 % yield with 84 % ee. In this reaction, NaHMDS was used as a base and Trost L-2 as chiral ligand [58]. Asymmetric allylation of the tetralone 164 with allyl acetate was carried out using Trost L-6 in the presence of CS2CO3 to provide the allylated ketone with 91 % ee in 90% yield [59]. 

A-(Diphenylmethylene)glycine t-butyl ester (t-butyl glycinate-benzophenone Schiff base) (171) is a reactive prochiral nucleophile and a-allyl-a-amino acids can be prepared by allylation and hydrolysis of the allylated product. Asymmetric allylation of 171 with cinnamyl acetate (41) afforded 172 regioselec-tively with high % ee when the reaction was carried out in presence of achiral phosphite P(OPh)3, and a ehiral phase-transfer catalyst of alkaloid [0-allyl-(9-anthracenylmethyOcinchonidinium iodide] [65,66]. 

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