Scope and Mechanism in Palladium-Catalyzed Isomerizations of Highly Substituted Allylic, Homoallylic, and Alkenyl Alcohols

Herein we report
the palladium-catalyzed isomerization of highly
substituted allylic alcohols and alkenyl alcohols by means of a single
catalytic system. The operationally simple reaction protocol is applicable
to a broad range of substrates and displays a wide functional group
tolerance, and the products are usually isolated in high chemical
yield. Experimental and computational mechanistic investigations provide
complementary and converging evidence for a chain-walking process
consisting of repeated migratory insertion/β-H elimination sequences.
Interestingly, the catalyst does not dissociate from the substrate
in the isomerization of allylic alcohols, whereas it disengages during
the isomerization of alkenyl alcohols when additional substituents
are present on the alkyl chain.