SYNTHESIS OF A CALICENE PRECURSOR FOR RET RO-DIELS-ALDER REACTIONS

In view of retro-Diels-Alder reactions (RDA reactions), the calicene p recursor 9 has been synthesized in a comparably simple four-step synth esis by dibromocarbene addition at dibenzobarrelene (10-->11, 44%), ha logen-lithium 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 ac cording to the results of 'Curie-Point' pyrolysis, only anthracene and no calicene 2 has been detected so far.