Synthese einer Calicen-Vorstufe für Retro-Diels-Alder-Reaktionen

Synthesis of a Calicene Precursor for Retro-Diels-Alder Reactions In view of retro-Diels-Alder reactions (RDA reactions), the calicene precursor 9 has been synthesized in a comparably simple four-step synthesis by dibromocarbene addition at dibenzobarrelene ( 10 → 11 , 44%), halogenlithium exchange followed by reaction with cyclopentenone ( 11→12 , 91%) and H₂O as well as HBr elimination ( 12→14→9 , 43%) (Scheme 5). First experiments with respect to the thermal behavior of 9 show that, although RDA reaction seems to be relatively easily occurring according to the results of ‘Curie-Point’ pyrolysis, only anthracene and no calicene 2 has been detected so far.