Synthesis of Low Generation Phenylenealkylene Dendrons as Nonpolar Building Blocks for a Dendrimer Construction Set

Abstract

The gram scale syntheses of first and second generation (G1 and G2) dendrons 1-4, and 35, based on aryl and alkyl moieties, by Suzuki-Miyaura cross-coupling are presented. Both a divergent and an accelerated convergent route are applied. In addition, first results on the synthesis of hyperbranched oligomers of AB₂ monomer 19 are reported.

Key words

dendrimers - dendrons - Suzuki-Miyaura cross-coupling - iododesilylation - building blocks

References

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20

Since TMS groups are not protective groups in the common sense, we prefer to use the term place holder, which precisely defines their function.

22

Two-dimensional Heteronuclear Multiple Quantum Coherence NMR experiment.

26

A more practical reason was the unfavorable synthesis protocol of the dibromo compound by Pd-catalyzed allylation of (3,5-dibromophenyl)trimethylstannane. In order to avoid the handling of tin compounds the diiodo analog was prepared by a different procedure.

34

Target molecule 28 was also synthesized by reaction of the(expensive) 3,5-dibromobenzyl bromide with allylmagnesium bromide.

37

Preliminary investigations on the corresponding G3 dendron (not shown) encountered the additional problem that the molar mass of this molecule could not be confirmed, since the applied methods (EI, FAB, MALDI-TOF) only showed much smaller fragments. The mass spectral analyses of TBDMS-protected dendrons 3 and 4 point to the sensitivity of the silyl group with the loss of methyl and tert-butyl groups.

39

The molar mass distribution of hyperbranched poly(phenylene)s, obtained by Suzuki cross-coupling of 3,5-dibromophenylboronic acid, was reported to show a large dependence from the used solvent system. The average number of repeating units was between 13 and 42 (7 examples), in one example 206 repeating units were achieved. [38]

45

No reference data were found.