Dendrimers with molecular weights ranging from ca. 2700 to 11 000 and from 16 to 64 homoallyl ether end groups were cross-linked using the Grubbs ring-closing metathesis reaction. A combination of SEC, MALDI-TOF-MS, and AFM were used to characterize the cross-linked nanoparticles. The data suggest a significant decrease in volume with cross-linking and a concomitant increase in rigidity, both of which can be controlled independently with a fair degree of precision.

Polyglycerol, porphyrin-cored dendrimers were synthesized by the click reaction of azide-cored polyglycerol dendrons and octaazidoporphyrin 19. The dendrons were synthesized divergently starting with TBDPS protected allyl alcohol 2. Two, three and four cycles of dihydroxylation-allyl etherification gave dendrons [G-2.5] 6, [G-3.5] 8, [G-4.5] 11, with four, eight, and sixteen alkene groups, respectively. Dendron 11 was readily prepared on large scale with an overall yield of 45%. Dendron 8 was deprotected and converted to the corresponding alkyne -and azide-cored dendron 13 and 15 in 89% and 75% yield, respectively. Dendron 11 was deprotected and converted to the corresponding alkyne -and azide-cored dendron 16 and 18 in 68% and 24% yield, respectively. Both the [G-3.5]-azide 15 and [G-4.5]-azide 18 were separately "clicked" to polyalkyne core 19 via the Huisgen 1,3-dipolar cycloaddition to afford 20 and 21 in 65% and 66% yield, respectively. Dendrimer 21 has a MW ~ 16,000 and 128 peripheral alkene groups.

A third generation Frechet-type dendrimer containing 24 allyl ether end-groups was synthesized, cross-linked using the ring-closing metathesis (RCM) reaction, and the core was removed hydrolytically without significant fragmentation. The results are analogous to those previously reported for homoallyl ether dendrimers (Wendland, M. S.; Zimmerman, S. C. J. Am. Chem. Soc. 1999, 121, 1389-1390) suggesting that the less readily available homoallyl ether dendrimers can be replaced by their allyl ethers analogues in a range of applications.

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