Gold(I)-Induced Rearrangements of Propargyl Derivatives: A Gas-Phase Study
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The gold(I)-induced rearrangements of a variety of propargyl derivatives (ethers, acetals, acetates, and carbonates) were explored in the gas phase with experiments in an ion-trap mass spectrometer as well as with computations at the M06/QZVP level. In accord with condensed-phase studies, it appears that propargyl ethers and acetals prefer 1,3-migrations to give allenes with the release of aldehydes. With propargyl acetates, we show that the preferred path is also a 1,3-migration of the acetate to give an allene species, but that a 1,2-migration to give a gold(I) carbene species is competitive. However, with the kinetic window of our gas-phase instrumentation, only systems that can be locked into a gold(I) carbene structure give carbenoid chemistry. Finally, we found that propargyl carbonates react with gold(I) species and release CO2 in the gas phase; the likely pathway involves sequential 1,3-migrations, leading to a propargyl ether. Overall, the results highlight the dynamic nature of gold(I)-induced rearrangements and the competition between 1,2-migrations, 1,3-migrations, and the bridged intermediates that link them.
