Synthesis and Cycloaromatization of Enyneallenes: New Model Systems for the Neocarzinostatin Chromophore

Abstract

Acceptor substituted dienediynes 10 with an endocyclic double bond were synthesized and submitted to cuprate 1,6-addition reactions. The resultant enyneallenes serve as new model systems for the neocarzinostatin chromophore since they undergo Myers cyclization to diradicals 12. If these possess a hydrogen atom at C-2’, rearrangement to α,β-unsaturated esters 13a/b takes place; with a crossover experiment it was shown that the hydrogen atom is transferred in an intramolecular fashion. In contrast to this, diradical 12c with two methyl groups at C-2’ abtracts hydrogen atoms from the solvent to give saturated ester 14c.