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·2LiCl or CuCN·2LiCl to afford 5-alkyl or 4-alkyl cyclopentenone regioisomers: the former conditions afford 5-alkyl substituted cyclopentenones via β-carbon elimination, whereas the latter result in the 4-alkyl substituted regioisomers with concomitant oxidation at the γ-position, via a free radical mechanism.