Frechet-type polyether dendrimers

Chiral //A(oxazolinc) ligands disubstituted at the carbon atom linking the two oxazolines by Frechet-type polyether dendrimers coordinated with copper(II) triflate were found to provide good yields and moderate enantioselectivities for Mukaiyama aldol reactions in water that are comparable with those resulting from the corresponding smaller catalysts.291 AgPF6-BINAP is very active in this reaction and the addition of a small amount of water enhanced the reactivity.292... 

Dendrimers are hyperbranched polymers that emanate from a single core and ramify outward with each subsequent branching unit [1,2]. In the commonly employed divergent synthesis, dendrimers can be prepared through sequential, alternating reactions of two smaller units, one of which has a point of bifurcation. As is described elsewhere in this volume, several classes of dendrimers are known, including polypropyleneimine (PPI), polyamidoamine (PAMAM), and Frechet-type polyether dendrimers [1,2]. 

Ethers are chemically and coordinatively more inert than amides. Indeed, Frechet-type polyether dendrimers prepared in solution demonstrate a broad spectrum of chemical and coordinative compatibilities. Accordingly, polyether dendron synthesis on solid support was developed, initially by Bradley and coworkers and later by Portnoy and Dahan Instead of the 3,5-dihydroxy benzyl alcohol derivatives used in the soluble Frechet-type dendrimers, a more SPOS suitable 3,5-bis(hydroxymethyl)phenol unit was conceived as a building block for the dendron construction. 

Parallel studies on PAMAM dendrimers, the Frechet type polyether den-drons, and other dendrimer families have generated an extensive list of unique properties driven by the dendritic state/ Figure 1.18 compares several significant physical property differences between the linear and dendritic topologies related to conformations, crystallinity, solubilities, intrinsic viscosities, entanglement, diffusion/mobility and electronic conductivity. 

Preparation of Frechet-type Polyether Dendrons and Aliphatic Polyester Dendrimers by Convergent Growth An Experimental Primer... 

In 2004, Fan and coworkers synthesized a series of chiral dendrimer hgands bearing a chiral diphosphine Pyrphos at the focal point of the Frechet-type polyether dendrons (Figure 4.6) [43]. The relationship between the primary structure of the dendrimer and its catalytic properties was established in the Rh-catalyzed hydrogenation of a-acetamidocinnamic acid (Scheme 4.5). High enantioselectivi-... 

Dendrimer based-BINAP polymers have been prepared from 124. A series of soluble dendritic mono-BINAP ligands with Frechet-type polyether wedges like 127 and dendritic poly-BlNAP ligands like 128 have been reported Ruthenium complexes of both classes of dendrimer were prepared and found to be comparable both in catalytic activity and enatioselectivity as homogeneous BINAP analogs in asymmetric hydrogenation reactions. 

Dendrons and dendrimers are the most intensely investigated subset of dendritic polymers. In the past decade, over 6,000 literature references have appeared dealing with this xmique class of structure-controlled polymers. The word dendrimer is derived from the Greek words dendri- (tree branch-like) and meros (part of), and was coined by Tomalia et al. about 20 years ago in the first full paper on poly (amidoamine) (PAMAM) dendrimers [47,72]. Since this early disclosure, over 100 dendrimer compositions (families) and 1,000 dendrimer surface modifications have been reported. The two most widely studied dendrimer families are the Frechet-type polyether compositions and the Tomalia-type PAMAM dendrimers. PAMAM dendil-mers constitute the first dendrimer family to be commercialized, and represent the most extensively characterized and best-understood series at this time [46]. 

J.M.J. Frechet, H. Ihre, and M. Davey. Preparation of Frechet-type polyether dendrons and aliphatic polyester dendrimers by convergent growth an experimental primer, in Dendrimers and Other Dendritic Polymers. J.M.J. Frechet and D.A. Tomaha, Eds. John Wiley Sons West Sussex, pp. 569-586, 2001. 

Most recently. Fan s group [66] readily synthesized a series of chiral diphosphane-functionahzed Janus dendrimers (up to 16 BNIAP units, 39) by using liquid-phase organic synthesis with the third-generation Frechet-type polyether dendron as the soluble support. The ruthenium complexes of these dendritic ligands were... 

PREPARATION OF POLYETHER DENDRIMERS BY ASSEMBLY OF FRECHET-TYPE DENDRONS AROUND A CORE... 

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