Chan rearrangement

The Chan rearrangement is a chemical reaction that involves rearranging an acyloxy acetate (1) in the presence of a strong base to a 2-hydroxy-3-keto-ester (2).

[1] This procedure was employed in the Holton Taxol total synthesis.

[2] The methylene bridge in the reactant with adjacent carbonyl and acetyl substituents is acidic and can be deprotonated by strong non-nucleophilic bases such as lithium tetramethylpiperidide or lithium diisopropylamide (LDA) as in an aldol reaction.

The thus formed enolate then attacjs the adjacent acetyl group through a short lived intermediate oxirane.

Acidic workup liberates the free hydroxyl group.