Gold(I)-Induced Rearrangements of Propargyl Derivatives: A Gas-Phase Study

Abstract

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.

A Gold(I)‐Catalyzed Oxidative Rearrangement of Heterocycle‐Derived 1,3‐Enynes Provides an Efficient and Selective Route to Divinyl Ketones

“…The nature of the critical points was checked by vibrational analysis. The M06 functional was expected to perform acceptably on the basis of literature studies . Because the experimental part of the study was carried out in the liquid phase, solvent (toluene) was simulated by using the polarized continuum method, within the SMD and IEF‐PCM schemes.…”

Gold-Catalyzed Homogeneous (Cyclo)Isomerization Reactions

“…The π-coordination of gold to the alkyne group of an ynamide substrate 6 promotes the formation of an electrophilic keteniminium ion 7 susceptible to a nucleophilic attack. Propargylic carbonate/ester substrates 8 are prone to rearrange under gold-catalysis, usually trough a 1,3- or 1,2-migration of the carbonate/ester group over the π-system toward either the allene intermediate 9 or the gold-carbene 10 , respectively (Ghosh et al, 2014; Swift and Gronert, 2016). Alkynes containing and internal nucleophilic functional group 11 can cyclize either in an exo-dig or endo-dig fashion leading to 12 and 13 .…”

Contiguous Quaternary Centers from a AuI‐Catalyzed Nazarov Cyclization

“…In the majority of cases cyclization is initiated either by [1,3]‐ or by [1,2]‐oxa migration, typically of acetate, that is triggered through alkyne activation by the catalyst. There appears to be a delicate balance between the factors that favor [1,3]‐ over [1,2]‐oxa migration , …”