Taming a Vinyl Cation with a Simple Al(OTf)3 Catalyst To Promote C−C Bond Cleavage

5 years ago

Taming a Vinyl Cation with a Simple Al(OTf)3 Catalyst To Promote C−C Bond Cleavage

Helena Damsen, Liang Fu, Meike Niggemann

A detailed mechanistic investigation identified the stepwise nature of the 1,3-aryl shift, which enables our recently disclosed Al3+-catalyzed insertion of unactivated alkynes into the sp2–sp3 C−C bond of benzyl alcohols. The selectivity for the rearranged product was found to be induced by the continued coordination of the aluminum catalyst to the rearranging species, which is encouraged by a reversible background reaction. This participation of the catalyst beyond the ionization step is unique in the realm of carbocation driven reactions and opens up the possibility of a catalyst-induced chiral induction in the future. Furthermore, the study represents a rare example of detailed mechanistic analysis of a reaction with a product selectivity that changes with increasing conversion. Never let go aluminum! Continued participation of the catalyst in a carbocation-driven reaction proved responsible for the selective induction of a highly unusual 1,3-carbon shift. Detailed mechanistic analysis explains why a vinyl cation undergoes an unexpected rearrangement, resulting in the net insertion of unactivated alkynes into a C−C bond in benzylic alcohols.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201700282