Aliphatic Ketone Claisen Rearrangement: Troubleshooting the Transetherification Step by Identifying a Stable Acid Catalyst

Abstract After optimization for retention of catalytic activity, 4‐chlorobenzoic acid emerged as the optimal catalyst for the aliphatic ketone Claisen rearrangement. The optimal catalyst enables a one‐pot, metal‐free, catalytic protocol from allylic alcohols to γ,δ‐unsaturated ketones. The optimized process tolerates a range of substrates, including substituents with acid‐labile protecting groups. Reaction monitoring and DFT studies of the aliphatic ketone Claisen process agree that the ultimate rearrangement step typically has the highest activation barrier.