Allylation palladacycles

A related planar chiral Co-based oxazoline palladacycle COP-X (46) was later found to be of higher synthetic utility as it permitted the use of benzimidates, [62] as well as allylic trifluoro- [63] and trichloroacetimidates [64, 65]. 46 was found to be superior to its ferrocene analogue 41 [61] in a number of aspects such as ease of... 

Kang J, Yew KH, Kim TH, Choi DH (2002) Preparation of bis [palladacycles] and application to asymmetric aza-Claisen rearrangement of allylic imidates. Tetrahedron Lett 43 9509-9512... 

Anderson CE, Donde Y, Douglas CJ, Overman LE (2005) Catalytic asymmetric synthesis of chiral allylic amines. Evaluation of ferrocenyloxazoline palladacycle catalysts and imidate motifs. J Org Chem 70 648-657... 

Nomura H, Richards CJ (2007) An investigation into the allylic imidate rearrangement of trichloroacetimidates catalyzed by cobalt oxazoline palladacycles. Chem Eur J 13 10216-10224... 

Oxidative phenolic coupling. Biosynthesis of the alkaloid narwedine (3) is known to involve oxidative phenolic coupling of norbelladine derivatives (1), but the usual oxidants for such coupling in vitro convert 1(R = H) into the oxomaritidine skeleton (4) rather than 3. A new biomimetic synthesis of 3 involves the palladacycle 2, formed by reaction of 1(R = CH3) with Li2PdCl4, which is known to form complexes with allylic amines or sulfides (8,176-177). Oxidation of 2 with thallium(III) trifluoroacetate effects the desired coupling to give 3. 

Enantiomeric purity, palladacycle applications, 8, 295 Enantioselective addition reactions, nucleophiles to allylic... 

A six-membered cyclic allylic carbonate 102 undergoes a palladium-catalyzed decarboxylative C-C bond cleavage to afford dienic carbonyl compound 104 [122]. Decarboxylation of the allylic carbonate moiety provides the driving force for production of the intermediate five-membered hetero-palladacycle 103, from which formal reductive cleavage takes place. 

NMR spectroscopy. Complex 22 was formed selectively by oxidative addition of allyl bromide to palladium(II) palladacycle 21. This structure is believed to result from cis oxidative addition of allyl bromide to palladacycle 21. 

Heterocyclic analogues of BINAP, such a< 2,2, 5,5 -tetramethyl-4,4 -bis(dipheny Iphosph and tested in the Heck reaction. Incorporaut sulfinyl group to a double bond elicits enj intramolecular Heck reaction. Optically ai ides are produced from (/ )-l-f-butylsulfinylcy Palladacycle (109) and its analogues ind rearrangement of allylic imidates. - For a thioamides, it is convenient to allylate thi dine. This process involves a thio-Claisen n Enantioselective deprotonation of ketones slum bis[yV-benzyl-N-(a-phenethyl)]amide.-- tonation of enolates. ... 

Palladacycle (109) and its analogues induce chirality of A -allylalkanamides during rearrangement of allylic imidates. For a synthesis of a-branched chiral 4-alkene-thioamides, it is convenient to allylate thioamides of (-F)-frany-2,5-diphenylpyrroli-dine. This process involves a thio-Claisen rearrangement. 

More generally, it has been reported that four-, five-, six-, eight-, and twelve-membered rings of bicyclic carbonates can be opened. An example of the six-membered ring opening is given in Eq. 21 [46]. In the reaction, oxidative addition of the allylic C-0 bond toward Pd(0) species followed by decarboxylation affords a palladacycle intermediate. The subsequent p-carbon elimination results in the formation of a dienal. 

The alkylpalladium(IV) complexes obtained by oxidative addition of alkyl (methyl, allyl, and benzyl) halides to the palladium(ll) metallacycle spontaneously undergo reductive elimination. This implies migration of the alkyl group R onto the aromatic site of the palladacycle (Eq. 19, R=CH2Ph, 72% yield). 

The utilization of allylic alcohols as terminating agents of the palladacycle reaction sequence offered new access to a class of ketones or aldehydes containing the selectively substituted biphenyl unit. An example of the reaction is given by Eq. 44 (93% yield) [51]. 

These complexes show high catalytic activity (0.5 mol% loading) in short reaction times for the aryl amination of aryl chlorides, triflates, and bromides. Primary and secondary amines, both alkyl and aryl, are well tolerated. The mirroring of results can be emphasized if these palladacycles are compared to the (NHC)Pd(allyl)Cl systems, supporting the idea of identical active species [NHC-Pd] during the catalytic cycle. One of the limitations of these catalytic procedures or catalysts is their hmited activity for the couphng of electron-rich heterocycles with aryl hahdes. 

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). 

Highly vmsaturated lactone 403 was obtained by an intramolecular reaction of 2-(propargyl)allyl phosphate 398 with CO (1 atm) catalyzed by ligandless Pd catalyst in the presence of Cy2NMe. As an explanation, the acylpalladium 400 is converted to the ketene 401, and the palladacycle 402 is generated by oxidative cyclization. Insertion of CO to 402 and reductive elimination provide 403 [154]. 

It was also recently demonstrated that homocoupling of aryl and heteroaryl iodides could be efficiently catalyzed either by a palladacycle catalyst in the presence of amine in or by a (7r-allyl)palladium complex and TBAF in DMSO. Also, homocoupling of a variety of substituted halothiophenes was achieved in the presence of a catalytic amount of Pd(OAc)2 and diisopropylethylamine in toluene. ... 

Mechanistically, this reaction can be understood on the basis of the Jolly mechanism. As before, oxidative coupling affords the palladacycle 12, and protonation (adding Ha+ in an Se fashion) leads to the chelated 7r-allyl intermediate 13. In the absence of a good nucleophile, 13 loses proton Hb to afford a palladium(O) complex of the observed triene product (Scheme 4). It should be noted that the initially formed triene may subsequently undergo Pd-catalyzed double bond isomerization and thus in some cases product mixtures will be observed. 

The catalytic cycle in Scheme 21 is adapted from that proposed by Jolly et al. " for the dimerization of 1,3-butadiene with intermolecular trapping as discussed above. In the model the bisdiene coordinates around a reduced palladium center (e.g., 66) and undergoes oxidative addition with cyclization (oxidative coupling) via the yyn-addition of carbon and palladium across the diene to afford the intermediate palladacycle 68. Protonation of the Tj -allyl in an Se2 fashion leads to the aUcene complex 69, and stereospecific anfi-addition... 

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]. 

Table 8.1 Rearrangement of allylic imidate catalyzed by the palladacycle catalysts/AgOOCCFj in CH2H2...

A chiral TRIP anion combined with a palladacycle provides an active catalyst for enantioselective rearrangement of allylic imidates to the corresponding amide products (Scheme 98). Although the catalyst contains a chiral palladacycle, the stereoselectivity is induced by the chiral phosphate anion (Scheme 98). 

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