Biphenol derivatives

Mikami and co-workers16-19 have done extensive work for developing catalysts for the asymmetric carbonyl-ene reaction. Excellent enantioselectivites are accessible with the binol-titanium catalyst 17 (Equation (10)) for the condensation of 2-methyl butadiene (R1 = vinyl) and glyoxalates (binol = l,T-binaphthalene-2,2 -diol).16 The products were further manipulated toward the total synthesis of (i )-(-)-ipsdienol. The oxo-titanium species 18 also provides excellent enantioselectivity in the coupling of a-methyl styrene with methyl glyoxalate.17 Reasonable yields and good enantioselectivites are also obtained when the catalyst 19 is formed in situ from titanium isopropoxide and the binol and biphenol derivatives.18... 

A second set of ligands was prepared on the basis of biphenol as backbone for the cyclic structure. This results in a seven-membered rather than a five-membered ring as compared to the catechol-based phosphites, furthermore, the biphenol derivatives can be expected to be sterically more demanding than catechol ligands. 

The catechol-based hgands 14 show fairly low selectivity similar to that of the unmodified system. In contrast, the biphenol-derived phosphites 17 gave excellent chemoselectivity. The best results were obtained with 17c, where a TOP of ca. 1900 h was achieved which is close to the maximum value of 2000 h The n-selectivity of 71% was also appreciable, corresponding to an n/iso ratio of 2.4. The substituents in the biphenol backbones in hgands 19 re-... 

Fukuzumi and co-workers described spectroscopic evidence for a ix-rf- ] -peroxo-(Cu )2 species stabilized with a fcidentate nitrogen ligand, but no (catalytic) oxidation behavior towards catechol was noted (a related trinu-clear copper species converted 2,4-di-ferf-butylphenol stoichiometrically towards the biphenol derivative) [224], Stack et al. have described a similar ] -peroxo-(Cu )2 species (28, vide supra) that could be considered a structural and functional model for tyrosinase-activity, as it efficiently reacted with catechol, benzyl alcohol and benzylamine to yield quinone (95%), benzaldehyde (80%) and benzonitrile (70%) [172,173]. This dinuclear per-0X0 species is generated by association of two monomeric copper centers, in contrast to the systems based on dinucleating Ugand scaffolds described above. 

The Ullmann coupling is the classical example of Cu-catalyzed biaryl coupling, wherein (a) a phenol and arylhalide substrate are converted to a bis-arylether or (b) two arenes are coupled to form a bis-arene species. These coupling reactions are of great importance for general organic synthesis as well as pharmaceutical and fine chemicals. The copper-catalyzed phenol coupling to arrive at chiral biphenol derivatives is used extensively as a test reaction for the catalytic activity of new copper complexes [254,255]. 

The isomers correspond to 84% occupation of the benzidine site and 16% occupation of the biphenol site. The preferential occupation of the benzidine site was expected from the prior model work, mentioned above, involving the corresponding simple benzidine and biphenol derivative guests. 

Stable pentacoordinated allylsiliconates have been employed in aldehyde addition reactions. These reagents require no activation by Lewis acids or Lewis bases, but have found only limited applications in synthesis to date. The use of these agents in addition to aldehydes was first described in 1987 by Corriu [59] and Hosomi [60] and by Kira and Sakurai [61] in 1988. In these reactions, the addition of a catechol or 2,2 -biphenol-derived allylsiliconate to an achiral aldehyde led to the highly regio- and stereoselective formation of homoallylic alcohols. For example, the addition of the catechol-derived 2-butenylsiliconate 81 (90/10 E Z) provided a diastereomeric mixture of homoallylic alcohols 74 and 75 in a 90/10 ratio (Scheme 10-33) [60c]. 

The halodienones can also be reacted with other phenols to give the biphenol derivatives in the presence of silver perchlorate (equation 97) . 

Biphenol derivatives are quite resistant to hydrolysis and oxidation and have excellent electrical characteristics. The more highly chlorinated types are flame resistant and impart this quality to resins with which they are used. They are of special interest in chlorinated rubber, paints, and PVC electrical compositions. 

The report also described the preparation of two other polystyrene-based, supported Mo catalyst systems that employed a chiral binaphtholate scaffold [79]. Supported catalysts 87 and 88 were prepared in the same manner as that used for the previously described biphenolate derivatives. Interestingly, 87 compared... 

Later, Schaus group reported a new organocatalytic enantioselective example of Petasis reaction employing chiral biphenol-derived diol 30 as effective catalyst to promote... 

Obviously, a total redesign was needed if a significant advance was to be made in this area. This breakthrough was achieved in Miami, where Kaifer and Bissell took the decision to remove the hydroquinol ring from the system. Modelling studies on benzidine and biphenol derivatives showed that they are both included into the cavity of the tetracationic cyclophane and that the benzidine unit is included preferentially. The control in such a system was found to be possible on two fronts - chemical (through protonation of the benzidene nitrogen atoms) and electrochemically (on account of the low oxidation potential of the benzidene unit). 

Bidentate biphenol-derived diphosphites claimed by Oxeno (today Evonik) can be symmetric like 1 [92] or nonsymmetric, exemplified with 2 [44] and 3 (Figure 2.24) [93]. 

Scheme 19.55 Asymmetric MPV alkynylations catalysed by the aluminium complex of biphenol derivative.

Broad biological potential of enantiopure 1,2-dihydroquinolines prompted the recently reported organocatalytic, asymmetric Petasis reaction, catalyzed by chiral biphenols [31]. Since it was observed that chiral biphenol derivatives XXVI-XX-VIII serve as proficient catalysts for asymmetric reactions involving boronates [32, 33], the authors postulated that they could be used as ligands in multi-component condensation reactions, and the Petasis reaction in particular. 

Inspired by these results, Ko and coworkers subsequently obtained the directly related homoleptic, discrete complexes supported by biphenol-derived benzenesulfonate monoanionic ligands bearing a CF3 (57) or a OMe (58) substiment in para position of the sulfonate aromatic ring [74] (Fig. 17). The authors reported that in the presence of 2 equiv of BnOH, these complexes yielded potent binary catalyst systems for the ROP of CL (400 equiv, 25 °C) and TMC (200 equiv, 0-25 °C). The electron-withdrawing group in 57 allowed enhanced activity in comparison with 58 ... 

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