Anthracene-maleimide Diels-Alder adduct

Boydston and co-workers recently revisited the mechanochemical chain scission of star-shaped polymers in acoustic fields using a fluorogenic tum-on mechanophore (Fig. 30a) [232]. They synthesized PMA-L 61.6 and PMA-S3 28.6/ 85.9 with Mspan = 2Maim = 57.2 kDa (Fig. 30b). In both samples they linked one of the PMA arms to the core by an anthracene-maleimide Diels-Alder adduct. This mechanophore was previously studied by Bielawski and co-workers [57, 58]. Upon cycloreversion by mechanical force, it produces an anthracene moiety which displays strong UV-Vis and photoluminescence signals. 

Fig. 30 (a) Anthracene-maleimide Diels-Alder adduct that can generally fluoresce an anthracene moiety upon mechanical force, (b) Mechanophore-containing star and linear polymers bearing similar (c) Photoluminescence spectra in DMF of PMA-S3 28.6/85.9 upon increasing... 

Figure 1.11 Fujita s self-assembled coordination cage, which is prepared by simple mixing of an exo-tridentate organic ligand and end-capped Pd (I I) ion in a 4 6 ratio. Cache optimized structure of the ternary complex anthracene-maleimide metallocage. Molecular structure ofthesyn-isomerofthe 1,4-Diels-Alder adduct.

Figure 19 Diels-Alder reactions of (a) anthracene, (b) triphenylene, and (c) naphthalene with maleimide inside cage 5. (d) The crystal structure of the Diels-Alder adduct of 2,3-diethylnaphthalene within the cage.

Molecular dynamic simulations show that the confined space of SWCNTs may influence both the kinetics and thermodynamics of the Diels-Alder reactions between anthracenes and N-substituted maleimide guests, favoring an unusual regioselectivity. Thus, in the confined space of CNTs, the 1,4-exo adduct of a Diels-Alder cycloaddition may be produced instead of the 9,10-adduct, which is favored in bulk. It is possible that the nanotube chirality could influence the outcome of the reaction, as this could alter the preferred orientation of the reactants inside the SWCNT. However, it was snspected that the diameter of the SWCNT is likely to have by far the largest influence on the reaction outcome, as this will have the biggest influence on how close the reactants can approach each other [195]. 

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