Diels scandium complex with

A chiral scandium complex with a new ferrocenyl-based chiral diol ligand, FER-RODIOL, was reported to be an effective catalyst for enantioselective Diels-Alder... 

Lanthanide triflates catalyse Diels-Alder reactions, with the scandium complex as the most effective catalyst, and, again, the catalyst can be recovered and reused, being just as effective in subsequent runs. 

Fukuzawa et al. [99] found analogous scandium(III)triflate/ Pr-PyBOx complex as efficient catalyst for the asymmetric Diels-Alder reaction between cyclopentadiene or acyclic dienes and acyl-l,3-oxazohdin-2-ones with up to 90% ee. They latter described the same reaction in super critical CO2 in the presence of MSdA [ 100] that proceeded more rapidly than in CH2CI2 leading to the expected product with analogous selectivity. 

Kobayashi reported an asymmetric Diels-Alder reaction catalyzed by a chiral lanthanide(III) complex 24, prepared from ytterbium or scandium triflate [ Yb(OTf)3 or Sc(OTf)3], (Zf)-BINOL and tertiary amine (ex. 1,2,6-trimethylpiperidine) [30], A highly enantioselective and endose-lective Diels-Alder reaction of 3-(2-butenoyl)-l,3-oxazolidin-2-one (23) with cyclopentadiene (Scheme 9.13) takes place in the presence of 24. When chiral Sc catalyst 24a was used, asymmetric amplification was observed with regard to the enantiopurity of (/ )-BINOL and that of the endoadduct [31 ]. On the other hand, in the case of chiral Yb catalyst 24b, NLE was affected by additives, that is, when 3-acetyl-l,3-oxazolidin-2-one was added, almost no deviation was observed from linearity, whereas a negative NLE was observed with the addition of 3-pheny-lacetylacetone. 

The hetero-Diels-Alder (HDA) reaction of 2,3-dimethylbuta-1,3-diene and cyclohexa-1,3-diene with ethyl glyoxylate catalysed by chiral Zn(II) complexes yields both the dihydropyran and the ene product, the former predominating. The enantiomeric excess, which can reach 87%, is dependent on the solvent as well as the catalyst <97JCS(P1)2345>. Use of (Rs,E)-3-[(15)-isoborneol-10-sulfinyl]-l-methoxybutadiene gives the 5,6-dihydropyran with good endo and facial diastereoselectivity <97TA2989>. Scandium(III) perfluoro-octanesulfonate is an efficient catalyst in the HDA reaction of aldehydes with non-activated dienes <97BCJ1421>. 

Further examples also show particularly impressive selectivity. Kiindig has used the cationic iron catalyst (8.83) in the Diels-Alder reaction to give cycloadduct (8.85). The ruthenium (BINAP) catalyst (8.86) effects the Diels-Alder reaction of cyclopentadiene with 2-substituted acrylates with ees up to 99%. Kobayashi has shown that lanthanide and scandium triflate complexes of BINOL with 1,2,6-trimethylpiperidine, formulated as complex (8.87), are effective with oxazohdinone-based substratesand gives good selectivity in the formation of the Diels-Alder product (8.52). 

Later, several bisimine and diol-based chiral ligands were examined as Sc(OTf)3 complexes in the asymmetric Diels-Alder reaction of cyclopentadiene with 3-acryloyloxazolidin-2-one in the presence of 2,6-lutidine [134]. The scandium-salen complex was revealed to be the most effective catalyst and gave the endo adduct in 81% yield with 85% ee (endo/exo = 89/11). 

A comparative study on the influence of different lanthanide cations and the substituents at the 4 and 5 -positions in the pybox ligands in the Diels-Alder reaction of cyclopentadiene with 3-acryloyl-l,3-oxazolidin-2-one was realized [135], Of the catalysts derived from (4 P,5 P)-4-Me-5-Ph-pybox, the Sc(III)-based one is both strongly endo selective (endo/exo = 97/3) and highly enantioselective (97% ee (endo)). Later, it was found that the scandium-(4 S,5 S)-4-CH20TIPS-5-Ph-pybox complex also gave endo selective (endo/exo = 92/8-96/4) and highly enantioselective (93-99% ee (endo)) for the Diels-Alder reactions of cyclopentadiene with 3-acryloyl-or 3-crotonoyloxazolidinones. 

Thus, the reaction in aqueous Cu(N03)2 solution proceeded about 800 times faster than in water alone and 250000 times faster than in acetonitrile. This Lewis-acid-catalyzed aqueous Diels-Alder reaction presumably occurs via a transition state such as 2.50 with bidentate complexation to the metal as shown. In a related study, Kobayashi reported that scandium triflate can be used as a water-tolerant Lewis-acid catalyst for a Diels-Alder reaction in (9 1) tetrahydrofuran-water (THF-H2O) [30], though this mixed solvent system cannot take advantage of the hydrophobic effect observed in pure water or highly aqueous mixtures. 

Anwander and cowotkers (Gerstberger et al., 1999) immobilized rare-earth complexes on the mesopororrs silicate MCM-41 by first grafting [R N(SiHMe2)2 3(thf) c] onto MCM-41, followed by surface-confined ligand exchange with Hfod. This procedure yielded [MCM-41]R(fod) c(thf)3, (R = Sc, Y, La). The performance of this catalyst was tested in the hetero Diels-Alder reaction between trans-l-methoxy-3-trimethylsilyloxy-l,3-butadiene and ben-zaldehyde. A comparable activity was found for the yttiium(III) and scandium(III) com-... 

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