Atropisomer BINOL

Atropisomers of conformationally restricted bis-phenols have been popular ligands in several applications (Sch. 5, 8, 9, 11-13 Tables 4 and 5). Aluminum compounds prepared from bis-l,T-binaphth-2,2 -ol (BINOL) 40 and the derivatives 97 were examined as chiral catalysts in the reaction of methyl acrylate and cyclopentadiene by Maruoka, Concepcion and Yamamoto [50] and by Ketter, Glahsl and Hermann [47]. Four catalysts prepared from four derivatives of the 3,3 -bis-triarylsilyl derivatives of 97 and trimethylaluminum were examined in both toluene and dichloromethane the results are summarized in Sch. 26 [50]. Slightly higher asymmetric induction was observed in toluene and for the f-butyldiphenysilyl derivative 97b. The catalyst prepared... 

Apparently, much higher yields can be achieved in the oxidative coupling of 2-naphthol derivatives by means of Fe(III), Cu(I), Cu(ll), Mn(III), or Ti(IV) salts (Scheme 2.66) [27]. These reactions usually proceed very fast. Partially 0-protected binaphthols can be obtained by monoetherification of one hydroxy group via a modified Mitsunobu reaction [28]. Several methods allow the kinetic resolution of racemic atropisomers and, hence, access to optically pure (R)- or (S) binaphthol (BINOL) [27]. 

FIGURE 4 Themal stability of atropisomers including BINOL. Chemical and photochemical isomerization of biaryl isomers. 

Binaphthyl is one of many atropisomers possible for binaphthyl systems. Two important examples are the 2,2 -diol called BINOL and the 2,2 -diphenylphosphine derivative called BINAP. When chiral ligands are used, chiral synthesis becomes possible. That is, an achiral reactant can be stereospecifically converted to a chiral product. 

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