ABSTRACT
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 ß-carbon elimination, whereas the latter result in the 4-alkyl substituted regioisomers with concomitant oxidation at the γ-position, via a free radical mechanism.
ABSTRACT
A comparison study of the Ru(II)-catalyzed rearrangements of allenyl- and alkynylcyclopropanols to the corresponding cyclopentenones has been undertaken with the aid of an alkyl substituent on the three-membered ring. These ring expansion reactions proceed with exceptional regioselectivity irrespective of the cis/trans stereochemistry of the substituents on the three-membered ring. ß-Carbon elimination is the common feature in the absence of a chelating group at the 4'-position in the alkyne chain.
