Siloxane fourth generation

Fig. 4.49 Synthesis of fourth-generation siloxane dendrimers (according to Muzfarov et al.)...

The first dendrimers of this type were reported by Rebrov and coworkers in 1989154. Reaction of MeSiC with (EtO MeSiONa followed by reaction with SOCI2 gave the SiCl-terminated first generation. Repetition of the (EtO MeSiONa and SOCI2 sequences led to formation of siloxane dendrimers up to the fourth generation (Scheme 14). 

Ester-based cascades (e.g., 107) have been prepared[77 80i by using 5-(tert-butyldime-thylsiloxy)isophthaloyl dichloride (108), which was synthesized in high yield from 5-hydroxy-isophthalic acid (Scheme 5.26). The dendron wedges were prepared by treatment of siloxane 108 with phenol to give bis(aryl ester) 109, which was hydrolyzed, or desilylated (HC1, acetone), to generate a new phenolic terminus. Treatment of this free phenolic moiety with monomer 108, followed by hydrolysis, afforded the next tier (110). Repetition of the sequence followed by reaction of the free focal phenols with a triacyl chloride core, (e.g., 86), afforded the fourth tier dendrimer 107 of the polyester aryl series. It was noted that the choice of base (N, A-dimethylaniline) used in the final esterification was critical, since with pyridine bases (pyridine or 4-(dimethylamino)pyridine) facile transesterification resulting in branch fragmentation occurred. 

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