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Accordingly, the focal positions in this series are occupied by bromo substituents, which are necessary for the Heck coupling and are tolerated by the Horner condensation, and by formyl groups, which are necessary for the Horner reaction and are tolerated by the Heck process [40].

The attachment of special chromophores in the focal points of dendrimers requires reactions, which keep the molecules intact. Interesting examples have been found for the attachment of fullerene C60. The aldehydes 12a and 12d were first transformed to the p-nitrophenylhydrazones 12b and 12e, respectively, before the fullerene was fixed in 1,3-dipolar cycloadditions of the in-situ generated nitrilimines [46]:

NCS, C60 12b -12c

NCS, C60 12e -12f

A related, independently developed procedure allows the direct fixation of C60 by a 1,3-dipolar cycloaddition with the

Scheme 1. Continued.

aldehyde 12j in the presence of N-methyl-glycine (16, sar-cosine) [47]:

Ultimately, a synthesis will be mentioned here, in which the core is constructed in the final reaction step. The aldehydes 11b and 11d were condensed with pyrrole (17) in the presence of trifluoroacetic acid. The intermediate chlorins were oxidized with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone [44]. This so-called Lindsey synthesis [49] is an established method for the formation of the porphyrin ring system, which represents the core of the dendrimers 8a, b.

11b o

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