Dendron disassembly mechanism

FIGURE 5.4 Disassembly mechanism of first-generation self-immolative dendron. 

The disassembly mechanism of dendron 27 is illustrated in Fig. 5.22. Cleavage of the trigger initiates the cyclization of a dimethylurea derivative to release phenol 28. The latter can undergo 1,8-elimination followed by decarboxylation to release one reporter unit and to generate quinone methide 29. In the next step, a nucleophile (most likely a solvent molecule) presumably reacts with the highly electrophilic quinone methide to generate the phenol 30. Similarly, we hypothesize that one more 1,8-elimination and four 1,6-eliminations take place to lead to the release of all six reporters. 

Additional support for this disassembly mechanism was obtained by monitoring the release of the pyrene tail units by fluorescence spectroscopy. The confined proximity of the pyrene units in the dendritic molecule results in formation of excimers. The excimer fluorescence generates a broad band at a wavelength of 470 nm in the emission spectrum of dendron 31 (Fig. 5.25). Upon the release of the pyrene units from the dendritic platform, the 470 nm band disappeared from... 

FIGURE 5.22 Disassembly mechanism of AB6 self-immolative dendron 27. 

Scheme 26 Description of a Gl-dendron disassembly through a double triggering mechanism. Cleavage of either trigger I or II will initiate the release of the reporter group...

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