Scandium-BINOL complexes

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). 

Analogous addition with scandium-(5, 5 -2,6-bis(oxazolinyl)pyridine) complex resulted in lower enantioselectivity. A chiral heterobimetallic complex of Y(OTf)3 and Li-BINOL provided high ee in addition of 0-methylhydroxylamine to enones of type 55 (equation 36) . ... 

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. 

Kobayashi and coworkers have reported that a chiral complex derived from scandium(III)triflate, i -(-i-)-BINOL ((i )-59), and 1,2,6-trimethylpiperidine in the presence of 4 A molecular sieves catalyzes the reaction of unsaturated imides with cyclopentadiene in 96-97% ee (Scheme 49) [130]. 

The catalytic asymmetric Michael reaction using silyl enol esters (Mukaiyama-Michael reaction) as the pronucleophiles has been reported using a titanium/BINOL catalyst (in up to 90% ee). Considering furan (11.36) as a silyl enol ether, this has been shown to undergo nucleophilic addition to the Michael acceptor (11.37). The product (11.38) canbe obtained with excellent diastereocon-trol with the scandium complex of hgand (11.39), or with excellent enantiocontrol... 

The first example of the use of rare earth metal complexes for asymmetric catalysis in organic solvents was reported in 1983 in chiral europium-catalyzed hetero Diels-Alder reactions. As for scandium catalysts, the first chiral catalyst was reported in 1994. Diels-Alder reactions using a chiral catalyst prepared from Sc(OTf)3, (/ )-BINOL, and an amine afforded the desired products in up to 97% ee. Following these results, many chiral rare earth metal catalysts have been developed. 

In the presence of the chiral scandium catalyst, the 1,3-dipolar cycloaddition of benzylbenzylideneamine A-oxide with 3-(2-butenoyl)-1,3-oxazolidin-2-one proceeds to yield the endo adduct (endo/exo 99/1) in 69% ee (eq 25). Chiral scandium complexes prepared from Sc(OTf)3 and 2,2 -bis(oxazolyl)-BINOL derivatives also serve as efficient catalysts. ... 

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