Mechanism of the Gold(I)-Catalyzed Rautenstrauch Rearrangement:  A Center-to-Helix-to-Center Chirality Transfer

The mechanism of the stereospecific gold(I)-catalyzed Rautenstrauch rearrangement of (E)-1-ethynyl-2-methyl-but-2-en-yl acetate to 3,4-dimethyl-cyclopent-2-enone has been computationally addressed using DFT (B3LYP/6-31G*, SDD for Au). Our results indicate that the bond formation event follows the Au(I)-induced acetyl transfer to the vicinal alkyne and that it is the helicity of the pentadienyl cation intermediate which keeps memory of the chiral information. The fidelity of the center-to-helix-to-center chirality transfer requires that the rates of helix interconversion and pivaloyl rotation are slower than the cyclization, as calculations predict.