Binaphthyl template

Table 1. Chiral phase transfer catalysts based on the binaphthyl template developed between 1998 and 2001...

Our template synthesis of knots implies that the target molecules are obtained as cationic dicopper(I) complexes. Therefore we considered the possibility of interconverting both enantiomers into a pair of diastereomeric salts [137, 138] by combining them with an optically active anion. Binaphthyl phosphate (BNP") [139] drew our attention because its chirality arises from the binaphthyl core, which is twisted. This helical structure is of the same type as that of die copper double helix, precursor of the knot. Besides, both compounds are aromatic and, thus, we could expect some potentially helpful stacking interactions [87],... 

Diols such as the optically active 1,1 -binaphthyl-2-2 -diol (BINOL) have been used as versatile templates and chiral auxiliaries in catalysts employed successfully in asymmetric synthesis. The application of enzymes in the enantioselective access to axially dissymmetric compounds was first reported by Fujimoto and coworkers.83 In aqueous media, the asymmetric hydrolysis of the racemic binaphthyl dibutyrate (the ester) using whole cells from bacteria species afforded the (A)-diol with 96%ee and the unreacted substrate (A)-ester with 94% ee at 50 % conversion. Recently, in non-aqueous media, lipases from Pseudomonas cepacia and Ps. fluorescens have been employed in the enantioselective resolution and desymmetrization of racemic 6,6 -disubstituted BINOL derivatives using vinyl acetate.84 The monoacetate (K)-73 (product) was obtained in 32-44 % chemical yields and 78-96% ee depending on the derivatives used. The unreacted BINOL (S)-72 was obtained in 30-52 % chemical yield and 55-80% ee. 

In a series of papers [23], Tamai et al. reported using l,r-binaphthyl isomers as templates for a diastereoselective synthesis of ester alcohols from the corresponding acyl compounds. They reported a low d.e. of 16% of the ester alcohol [Eq. (8) 23c]. However, their more recent modifications gave improved yields and higher diastereoselectivities. When they added a polyether as a 2 -substituent and lengthened the chain between the dicarbonyls, the 7 -isomer was formed exclusively. Hydrolysis of this product yields the / -lactone. The authors suggest that the cooperative chelation of the oxygen side chain plays an important role in the exclusive formation of the / -enantiomer. 

Scheme 10-130 Methyl 7-deoxycholate provides a chiral template for the enantioselective synthesis of the binaphthyl compound 401.

In non-enzymatic asym. synthesis, centre stage goes to homochiral reagents with C2-symmetry . Chiral stein (1,2-diamino-1,2-di-phenylethane) derivatives, for example, are prominent in a variety of standard transformations, although the dimethoxy-analog evidently is superior for asym. 1,4-addition to a,P-unsatd. azome-thines" . Equally valuable are axially asymmetric biaryl and binaphthyl derivs. which (like stein derivs.) may coordinate a metal template for enhancement of enantioselectivity or incorporation of... 

Unlike the asymmetric hydrosilation of alkenes and acetylenes where Pd catalysts seem to dominate activity, for enantioselective hydrosilation of ketones a preponderance of Rh-based catalysts have been used, although a few other metals including Pd have been examined and some ligand templates such as binaphthyl are in common. 

---