Enantiomeric purity BINOL derivatives

Me02CCH0/H+ -7.90 eV, vide infra), by the BINOL-Ti catalyst (1) (Table 1). The reaction was carried out by simply adding an olefin and tfien freshly dehydrated and distilled fluoral (2a) at 0 C to the solution of the chiral titanium complex (1) prepared from (/ )- or (5)-BINOL and diisopropoxytitanium dihalide in the presence of molecular sieves MS 4A as described for die glyoxylate-ene reaction (5). The reaction was completed widiin 30 min. The ene-type product, namely homoallylic alcohol (3) was obtained along with the allylic alcohol (4) (entries 1-4). The enantiomeric purities of both products were determined to be more than 95% ee by 1h NMR analysis after transformation to the (5)- and (/ )-MTPA ester derivatives. Thus, the absolute configuration of the products was determined by the Mosher method (8). The sense of asymmetric induction is, therefore, exactly the same as observed for the glyoxylate-ene reaction the (/ )-catalyst provides the (/ )-alcohol products (5). 

A related Mukaiyama aldol catalyst system reported by Keck prescribes the use of a complex that is prepared in toluene from (R)- or (S)-BINOL and Ti(0 Pr)4 in the presence of 4 A molecular sieves. In work preceding the aldol addition reaction, Keck had studied this remarkable catalyst system and subsequently developed it into a practical method for enantioselective aldehyde allylation [95a, 95b, 95c, 96]. Because the performance of the Ti(IV) complex as an aldol catalyst was quite distinct from its performance as a catalyst for aldehyde allylation, a careful examination of the reaction conditions was conducted. This meticulous study describing the use of (BINOL)Ti(OiPr)2 as a catalyst for aldol additions is noteworthy since an extensive investigation of reaction parameters, such as temperature, solvent, and catalyst loading and their effect on the enantiomeric excess of the product was documented. For example, when the reaction of benzal-dehyde and tert-butyl thioacetate-derived enol silane was conducted in dichlo-romethane (10 mol % catalyst, -10 °C) the product was isolated in 45% yield and 62% ee by contrast, the use of toluene as solvent under otherwise identical conditions furnished product of higher optical purity (89% ee), albeit in 54% yield. For the reaction in toluene, increasing the amount of catalyst from 10 to 20 mol %... 

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