TADDOL-derived ligands

CU4S4] species in which the TADDOL-derived ligand was an unexpected sul-fur-monodentate and not a S/X-bidentate ligand. This hypothesis was confirmed by NOE NMR spectroscopy that suggested a different structure for the Cu complex of the alcohol ligand relative to the methylether and the dimethylamino ligands, which could explain the observed stereochemical inversion. 

Scheme 2.8 Cu-catalysed addition of w-BuMgCl to cycloheptenone with TADDOL-derived ligands.

Scheme 24 Pd-catalyzed enantioselective aylation of cyclopropanes in the presence of TADDOL-derived ligand 86...

ArMgBr (1.5 equiv) CuBr-SMej (4 mol%) Taddol-derived ligand (6 mol%)... 

Michael addition of Grignard reagents ArMgX to enones can be catalysed by the Cu complex of the TADDOL-derived ligands (474) (4 mol%) in Me-THF at -78 C with <95% ee Other A-heterocyclic Cu complexes that catalyse the Michael addition of Grignard reagents to (cyclic) enones were derived from (475) and (476). ... 

The combination of [Rh(Cl(NBD)]2 and ligands 89, 90, 91, or 92 with diphenylsilane asymmetrically reduces aryl alkyl ketones, including acetophenones, in excellent yields and in 81 to 90% ee (Eq. 346).574 The best results are with ferrocene 91 and acetophenone in toluene.575 Other phosphine-substituted ferrocenes do not give comparable results. Rhodium(I) complexes of TADDOL-derived... 

Nonetheless, among bidentate diphosphines and with the notable exception of BINAP 23, there have been only sporadic examples of ligands whose rhodium complexes give enantioselectivities above 85% in hydroboration Knochel s dicyclohexylphosphine 34,80 Togni s Josiphos 41,85 and TADDOL derivatives 48, 50-52.90 Even... 

Seebach et al. (154) showed that a 0-isopropylidene-2,3-dihydroxy-l, 1,4,4-tetraphenyl-l,4-diol (TADDOL)-derived aminothiolate serves as a moderately effective ligand for the catalyzed conjugate addition of Grignard reagents to cyclic enones. The catalyst, synthesized from the lithiothiolate and CuCl, exhibits optimal selectivities under a slow addition protocol (2 h), Eq. 124. 

The use of TADDOL-based ligands offers an important alternative for copper-catalyzed asymmetric 1,4-additions. TADDOLs (a, a, a, a -tetraaryl-l,3-dioxolane-4,5-dimethanol compounds), introduced by Seebach, are among the most successful currently known ligands in asymmetric catalysis. Seebach also developed the first copper-catalyzed 1,4-addition of a Grignard reagent using a TADDOL derivative as a chiral ligand (see Scheme 7.2) [17]. We have reported TADDOL-based... 

So far, few data are available which allow the comparison of differences in efficacy and selectivity of one catalytic system attached to different supports. As far as the TADDOLate complexes are concerned, no clear rules can be drawn. Polystyrene-based catalysts derived from (8) and (10) show similar enantioselectivities and reaction rates. Differences appear, however, when comparing them with a polystyrene-embedded dendritic ligand system, generated by co-polymerization from TADDOL-derivative (32) (Scheme 4.18) which is described in Section 4.3.2.1. Re-cydabihty seems to be easier for the dendritic catalyst and the enantioselectivity. 

Immobilization of TADDOL-derivatives to silica and treatment with various tita-nium(IV) salts furnished a catalytic system (38) which was utilized in [2-1-3] cycloadditions of diphenylnitrone and acylated oxazolidinone to yield oxazolines (Scheme 4.23) [65]. It is noteworthy that the ligand X has an impact on the outcome of this cycloaddition. While the dichloro catalyst affords the exo-adduct in good yield and with a high stereoselectivity, the corresponding tosyloxy catalyst preferentially affords the endo-cycloadduct. The efficiency of the process is comparable to those obtained with the analogous soluble catalysts. The catalyst, however, had to be recycled prior to each experiment. 

Lewis acid-promoted asymmetric addition of dialkylzincs to aldehydes is also an acceptable procedure for the preparation of chiral secondary alcohol. Various chiral titanium complexes are highly enantioselective catalysts [4]. C2-Symmet-ric disulfonamide, chiral diol (TADDOL) derived from tartaric acid, and chiral thiophosphoramidate are efficient chiral ligands. C2-Symmetric chiral diol 10, readily prepared from 1-indene by Brown s asymmetric hydroboration, is also a good chiral source (Scheme 2) [17], Even a simple a-hydroxycarboxylic acid 11 can achieve a good enantioselectivity [18]. 

A highly enantioselective synthesis of a-dehydroamino acids (186) with a stereogenic centre at the y -position has been developed, which employs a copper-catalysed asymmetric conjugate addition of diethylzinc to a,j3-unsaturated imines (185) with the TADDOL-derived phosphoramidite (187) as a chiral ligand.234... 

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