Asymmetric Synthesis of a Series of Chiral AB₂Monomers for Dendrimer Construction

Abstract

Efficient preparation of a series of four chiral, nonracemic AB 2 monomers suitable for the construction of dendrimers is presented. Monomers 1-4 possess the common structural features of a diphenolic moiety and a benzylic or aliphatic hydroxyl which render these molecules suitable for convergent dendrimer synthesis. The same basic, high-yielding, five-step sequence is employed for 1-4. Stilbene derivatives 13 and 14 are prepared by a Horner-Wadsworth-Emmons modified Wittig reaction between 3,5-or 3,4-bis(benzyloxy)benzaldehyde (8 and 10) and an ester-substituted benzylphosphonate (11 or 12). Cinnamate derivatives 21 and 22 are prepared similarly from 8 and 10 and triethyl phosphonoacetate. Chirality is introduced in the form of a 1,2-diol unit by Sharpless asymmetric dihydroxylation (AD) (>97% ee in all cases). Protection of the 1,2-diols as their acetonide derivatives provides dioxolane intermediates 17, 18, 25, and 26. Reduction of the ester groups followed by hydrogenolysis of the benzyl ethers yields AB 2 monomers 1-4 in 57-67% overall yield from 8 and 10.

Convergent Dendrons and Dendrimers: from Synthesis to Applications

“…In addition to the numerous examples of conjugated dendrimers previously discussed, 115,116,[119][120][121][122][124][125][126][127][128][129][130][132][133][134][140][141][142][143][144][145][146][147][148]497 the convergent approach has been demonstrated as a viable route toward the preparation of dendrimers with a range of repeat units including: fullerene, 498,499 quaternary ammonium salt, 177 pyridine, 382,500-502 TTF, 503-506 triarylamine, [171][172][173]507,508 carbazole, 509,510 azobenzene, 351,511-513 liquid crystalline, [514][515][516] and chiral repeat units. [96][97][98][99][100][101][102][103]…”

A Convenient Synthesis of the Echinacea-Derived Immunostimulator and HIV-1 Integrase Inhibitor (−)-(2R,3R)-Chicoric Acid

“…The mobile phase was MeCN/H 2 OÀHCO 2 H 99.5 : 0.5 and gradient elution (0 ± 50 min: 12 to 40% MeCN) was applied at a flow rate of 0.8 ml/min. Ethyl 3-[3,4-Bis(benzyloxy)phenyl]prop-2-enoate (6) [15]. Under stirring, to a soln.…”

Functionalizing the interior of dendrimers: Synthetic challenges and applications

“…In their investigations concerning chiral dendrimers, 60 McGrath and coworkers [61][62][63][64] reported on the incorporation of acetonide-protected vicinal diol units in poly(benzyl ether) dendrimers (Fig. 3).…”

“…57,58 Rather surprisingly, the acid-labile acetonide-protecting groups seemed to be compatible with the slightly acidic Appel-type bromination conditions (discussed later). Although much of the authors' primary attention was devoted toward the characterization of the acetonide-protected series, [61][62][63] some efforts were made to postmodify the synthesized dendrimers by the unmasking of the protected diol functionalities and by the investigation of the resulting compounds. 64 The deprotection of convergently grown dendrimer 5 under rather harsh conditions, i.e., 3 M HCl at 55°C, afforded polyol 6 in a modest yield.…”