Mechanism of the Gold-Catalyzed Rearrangement of (3-Acyloxyprop-1-ynyl)oxiranes: A Dual Role of the Catalyst

[GRAPHICS] The three competing paths for the rearrangement of 1 (involving 1,2- and 1,3-ester migration with alkyne or oxirane activation) evidence the multifaceted character of gold as a catalyst. The most favorable mechanism for this useful synthetic transformation involves a cascade of more than eight steps. All the functional groups in the substrate play a crucial and synergistic role, and sequential gold coordination to both the pi-system and the lone pairs of oxygen is needed. Exploration of these three paths suggests the use of a nonalkynophilic Lewis acid (BF3) as a possible synthetic alternative for this transformation.