Tetraaryl-1.3-dioxolane-4,5-dimethanols derivatives

Essentially concurrently, the C2-symmetric ketone catalysts 8—10 were reported72-73. In regard to the enantioselectivity, the TADDOL (a,a,a, a -tetraaryl-l,3-dioxolane-4,5-dimethanol)-derived ketone 10 performs better than the binaphthalene-based ketone 6, but not as well as the fructose-modified ketone 7, whereas 10 is more resistant than 7 in regard to oxidative degradation73. 

TADDOL-(a,a,a, a -tetraaryl-l, 3-dioxolan-4,5-dimethanol)-derived gold complex in the presence of AgBF4 (Scheme 4-46). By using electron-rich A-heterocyclic carbene (NHC)-gold catalysts, an alternative pathway toward [3+2]-cycloaddition products can be favored. ... 

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... 

Seebach, D., Hayakawa, M., Sakaki, J. and Schweizer, W.B. (1993) Derivatives of tetraaryl-2,2-dimethyl-1,3 -dioxolane-4,5 -dimethanol (TADDOL) containing nitrogen, sulfur, and phosphorus atoms. New ligands and auxiliaries for enantioselective reactions. Tetrahedron, 49, 1711-1724. 

Nonracemic Ti-BINOLate (BINOL = l,l -bi-2-naplilli()l) and Ti-TADDOLate (TADDOL = a,a,a, a -tetraaryl-2,2-dimethyl-l,3-dioxolan-4,5-dimethanol) complexes are also effechve chiral catalysts for the asymmetric alkylation of aldehydes [9-11]. Seebach developed polystyrene beads with dendritically embedded BINOL [9] or TADDOL derivatives 11 [10, 11]. As the chiral ligand is located in the core of the dendritic polymer, less steric congeshon around the catalyhc center was achieved after the treatment with Ti(OiPr)4. This polymer-supported TiTADDOLate 14 was then used for the ZnEt2 addition to benzaldehyde. Chiral 1-phenylpropanol was obtained in quantitahve yield with 96% ee (Scheme 3.3), while the polymeric catalyst could be recycled many times. 

Tetraaryl-l,3-dioxolane-4,5-dimethanol (TADDOL) ligands synthesized from tartaric acid have been extensively employed by Narasaka as the chiral control element in selective Diels-Alder reactions. Initial experiments were conducted with simple dienes and a,P-unsaturated imides using complex 44 (Scheme 36) [104,105]. Several rather subtle features have contributed to the success of these endeavors 1) the use of the acetophenone-derived dioxolane rather than the ac-etonide resulted in an increase of 20% ee 2) the use of alkyl-substituted benzenes as solvent augmented enantioselectivities relative to more common organic solvents e.g., CH2CI2, THF) [106] 3) use of 4 A molecular sieves was typically required to achieve maximum enantioselectivity. 

Other enantioselective catalysts for the D-A reactions have been developed. The chiral ligands used include the TADDOLs (a, a, a, a-tetraaryl-l,3-dioxolane-4,5-dimethanols) ° and BINOL derivatives. These are discussed in Section 6.4 of Part B. 

Based on Frechefs work [20], Luis and coworkers [21] studied the influence of the mode of preparation of the polystyrene backbone functionalized with TADDOL (a,a,a, a -tetraaryl-l,3-dioxolane-4,5-dimethanol) 2. This immobilized ligand was loaded with titanium on the topicity of an asymmetric transformation. Here, the Diels-Alder reaction of cyclopentadiene with 3-crotonyl-l,3-oxazolidin-2-one was chosen as a model reaction. The TADDOL ligands were incorporated into the polymeric backbone either by polymerization using functionalized styrene derivative 1 or by grafting and coupling of phenol 2 to Merrifield-type resins (Scheme 7). 

Wu and his co-workers reported an experimental and theoretical study on the hydrogen-bond-promoted enantioselective hetero-Diels-Alder reaction (HAD) of Danishefsky s diene 105 with benzaldehyde 106, Scheme 3.37 [52], The reaction was achieved catalytically by a series of a,ct,a, a -tetraaryl-l,3-dioxolane-4,5-dimethanol (TADDOL) derivatives through hydrogen-bonding activation and afforded 2-phenyl-2, 3-dihydro-4H-pyran-4-one 108 in good enantioselectivity. 

We have investigated the mechanism of enantiomeric enrichment by enclathration by studying TADDOL type hosts (derivatives of Q ,Q ,Q , Q -tetraaryl-l,3-dioxolane-4,5-dimethanol) which enclathrated 2-butylamine mixtures of varying enantiomeric composition. In particular, the host (/J,.R)-(—)-tran5 -4,5-bis-(hydroxydiphenylmethyl)-2,2-dimethyl-1,3-dioxolane entraps different proportions of both enantiomers of 2-butylamine, depending on the initial composition of the mother liquor. The system is subtle, in that the compounds crystallize in PI with Z = 2 and the two independent host molecules behave differently. The selectivity curves of molecules 1 and 2, and the overall selectivity are shown in Figure 8. 

Toda et al carried out a pioneering work in the area of chiral recognition by a,a,a a -tetraaryl-l,3-dioxolane-4,5-dimethanol (TADDOL) derivative. They found... 

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