SYNTHESIS AND CYCLOAROMATIZATION OF ENYNEALLENES - NEW MODEL SYSTEMS FOR THE NEOCARZINOSTATIN CHROMOPHORE

Acceptor substituted dienediynes 10 with an endocyclic double bond wer e synthesized and submitted to cuprate 1,6-addition reactions. The res ultant enyneallenes serve as new model systems for the neocarzinostati n chromophore since they undergo Myers cyclization to diradicals 12. I f these possess a hydrogen atom at C-2', rearrangement to alpha,beta-u nsaturated esters 13a/b takes place; with a crossover experiment it wa s shown that the hydrogen atom is transferred in an intramolecular fas hion. In contrast to this, diradical 12c with two methyl groups at C-2 ' abtracts hydrogen atoms from the solvent to give saturated ester 14c .