Binaphthyl-based amino alcohols

Compared with asymmetric ethylation, reports on asymmetric phenylation are limited. We disclosed the enantioselective phenylation using diphenylzinc prepared in situ from phenyl Grignard reagent and zinc chloride. This method needs a stoichiometric amount of chiral amino alcohol DBNE 18 but good ee of 82% was achieved [32], A catalytic phenylation was examined using planar chiral compound 1 based on ferrocene, and chiral diaryl carbinols of moderate ee were provided from diphenylzinc and 4-chlorobenzaldehyde (Scheme 10) [33]. A catalytic and highly enantioselective phenylation was realized by binaphthyl-based chiral catalyst 23. In this reaction, the addition of 2 equivalents of diethyl-zinc against catalyst increases the yield and ee [34]. Recently, chiral amino alcohol DPMPM 9 was also reported to be an efficient catalyst for asymmetric phenylation [35]. 

The binaphthyl-based amino sulfonamide (5 )-3 and an amino acid (5 )-8 were also applied for the asymmetric aminojylation with nitrosobenzene (Scheme 17.14). In the presence of either (5 )-3 or (5 )-8, the aminoxylation of aldehydes proceeded smoothly, and subsequent reduction with sodium borohydride gave 2-aminoxyl alcohols with good to excellent enantioselec-tivity. In each case, (5 )-3 and (5 )-8, which have identical axial chirality, gave opposite enantiomers as major products. 

In marked contrast with the above-mentioned aminojgrlation using nitrosobenzene, when a binaphthyl-based amino alcohol (5 )-10 was employed as catalyst, the reaction of various aldehydes with nitrosobenzene proceeded smoothly to give hydrojg amination products in good yield with excellent enantioselectivity without forming amino grlation products (Scheme 17.16). ... 

B) amino alcohols used in asymmetric phenyl transfer reactions [71] (C) and (D) binaphthyl-based amino alcohols [72] and (e) BINOL-derived chiral ligand [73]. 

In 2002, Ha and coworkers [72a] reported the preparation of binaphthyl-based amino alcohols (Figure 7.9, C) and their application in the asymmetric diphenylzinc additions to aldehydes. The corresponding diarylmethanol derivatives were obtained with very high enantioselectivities (92—98% ee) and in excellent yields (95—98%). Curiously, aliphatic aldehydes were tested as well, but poorer enantioselectivities were obtained (66—68% ee). 

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