Cu-Mediated Rearrangements of Allenylcyclopropanols to Cyclopentenones: Two Divergent Pathways

Two CuCN-mediated rearrangement reactions of allenylcyclopropanols to cyclopentenones have been achieved by means of Et2Zn/CuCN center dot 2LiCl or CuCN center dot 2LiCl to afford 5-alkyl or 4-alkyl cydopentenone regioisomers: the former conditions afford 5-alkyl substituted cyclopentenones via beta-carbon elimination, whereas the latter result in the 4-alkyl substituted regioisomers with concomitant oxidation at the gamma-position, via a free radical mechanism.