BINOLs functionalized dendrimers

In 2002, Sasai et al. reported the synthesis of dendritic heterobimetal-lic multi-functional chiral catalysts, containing up to 12 l,l/-bi-2-naphthol (BINOL) units at their terminal positions (Fig. 9) [30]. On treating these functionalized dendrimers with AlMe3 and n-Buli, insoluble metallated Al-Ii-bis(binaphthoxide) generation x (GX-ALB) catalysts were obtained, which showed moderate catalytic activity in the asymmetric Michael reaction of 2-cyclohexenone with dibenzyl malonate (Scheme 4). 

During the past two decades the homogeneous and heterogeneous catalytic enan-hoselective addition of organozinc compounds to aldehydes has attracted much attention because of its potential in the preparation of optically active secondary alcohols [69]. Chiral amino alcohols (such as prolinol) and titanium complexes of chiral diols (such as TADDOL and BINOL) have proved to be very effective chiral catalysts for such reactions. The important early examples included Bolm s flexible chiral pyridyl alcohol-cored dendrimers [70], Seebach s chiral TADDOL-cored Frechet-type dendrimers [28], Yoshida s BINOL-cored Frechet-type dendrimers [71] and Pu s structurally rigid and optically active BlNOL-functionalized dendrimers [72]. All of these dendrimers were used successfully in the asymmetric addition of diethylzinc (or allyltributylstannane) to aldehydes. 

Figure 4.36 The peripherally BINOL-functionalized chiral dendrimers.

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