Chiral metal complexes Claisen rearrangement

BINAP, 127, 171, 191, 194, 196 olefin reaction, 126, 167, 169, 191 organic halides, 191 Pancreatic lipase inhibitors, 357 Pantoyl lactone, 56, 59 para-hydrogen, 53 Peptides, matrix structure, 350 Perhydrotriphenylene, crystal lattice, 347 Pericyclic reactions, 212 chiral metal complexes, 212 Claisen rearrangement, 222 Diels-Alder, 212, 291 ene reaction, 222, 291 olefin dihydroxylation, 150 Phase-transfer reactions asymmetric catalysis, 333... 

Chiral-Metal-Complex-Catalyzed Aliphatic Claisen Rearrangement... 

Therefore, we focus our attention only on the recent developments of chiral metal catalysis rather than acceleration or promotion by an equimolar amount of metal complexes. Excellent contributions based on main-group metals by more than one molar amount of Al"" and b"" [3] complexes in particular will be described in this chapter just as an introduction to metal-catalyzed Claisen rearrangement. 

I 2 Chiral-Metal-Complex-Catalyzed Aliphatic Claisen Rearrangement Tab. 2.8 Pd"-catalyzed enantioselective Claisen rearrangement. 

R] For an excellent review, see Mikami, K. Akiyama, K. Chiral-metal-complex-catalyzed aliphatic Claisen rearrangement. In The Claisen Rearrangement - Methods and Applications, Hiersemann, M., Nubbemeyer, U., Eds. Wiley-VCH Weinheim, 2007 pp 25-43. See also (a) Majumdar, K. C. Alam, S. Chattopadhyay, B. Tetrahedron 2008, 64, 597-643. (b) Enders, D. Knopp, M. Schiffers, R. Tetrahedron Asymmetry 1996, 7,1847-1882. 

Chichibabin reaction, advances in, 44, 1 Chiral induction using heterocycles, 45, 1 Chrom-3-ene chemistry, advances in, 18,159 Claisen rearrangements in heteroaromatic systems, 42, 203 in nitrogen heterocyclic systems, 8, 143 Complex metal hydrides, reduction of nitrogen heterocycles with, 6, 45 39, I Concept of aromaticity in heterocyclic chemistry, 56, 303... 

In sharp contrast, the late transition metals are more coordinative to soft carbon-carbon multiple bonds rather than hard oxygen. These binding modes are further classified into mono- and bi-dentate coordinations, depending on the ligands on the metal catalysts, or the substituent pattern in the Claisen diene systems and solvents employed. Bi-dentate coordination of the Claisen substrate is advantageous over the weak mono-dentate coordination of the Claisen rearrangement product, y,d-unsaturated carbonyl compounds, to release the metal complex allowing the catalytic cycle. Furthermore, enantiodiscrimination by chiral late transition metal complexes is based on the discrimination of two enantiotopic diene faces in the enantiomeric six-membered transition states. 

Recently, Hiersemann reported the first catalytic enantioselective Claisen rearrangement (Scheme 2.4) [11]. The 2-alkoxycarbonyl-substituted allyl vinyl ethers 11 are reactive under the Lewis acid catalysis. Therefore, the Claisen rearrangements proceed catalytically [12]. Usually the Lewis-acid-catalyzed Claisen rearrangement does not proceed catalytically because of a higher affinity of the carbonyl product for the Lewis acids than the ether substrate. But this 2-alkoxycarbo-nyl-substituted substrate 11 can coordinate to metals in a bidentate fashion. This 2-alkoxycarbonyl substrate has higher affinity for Lewis acidic Cu complexes than the simple ether substrate. In this system, chiral copper (II) bisoxazoline Cu (box) complex 13 is effective for the enantioselective Claisen rearrangement. 

If the Claisen rearrangement is carried out with peptide allylic esters, the transfer of an allylic side chain to the a-position of the C terminal amino acid results in a modification of the peptide chain. This concept is comparable to the alkylations of peptide enolates described by Seebach et al. [93]. If it is possible to carry out the rearrangement not only with amino acids but also with peptide esters, the question arises if it is possible to transfer the chiral information from the peptide chain to the new chiral center formed during the rearrangement process, prohahly via some peptide metal enolate complexes. 

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