Catalyst‐Controlled Divergent Generations and Transformations of α‐Carbonyl Cations from Alkynes**

Abstract

Abstractα‐Carbonyl cations are the umpolung forms of the synthetically fundamental α‐carbonyl carbanions. They are highly reactive yet rarely studied and utilized species and their precursors were rather limited. Herein, we report the catalyst‐controlled divergent generations of α‐carbonyl cations from single alkyne functionalities and the interception of them via Wagner–Meerwein rearrangement. Two chemodivergent catalytic systems have been established, leading to two different types of α‐carbonyl cations and, eventually, two different types of products, i.e. the α,β‐ and β,γ‐unsaturated carbonyl compounds. Broad spectrum of alkynes including aryl alkyne, ynamide, alkynyl ether, and alkynyl sulfide could be utilized and the migration priorities of different groups in the Wagner–Meerwein rearrangement step was elucidated. Density functional theory calculations further supported the intermediacy of α‐carbonyl cations via the N−O bond cleavage in both the two catalytic systems. Another key feature of this methodology was the fragmentation of synthetically inert tert‐butyl groups into readily transformable olefin functionalities. The synthetic potential was highlighted by the scale‐up reactions and the downstream diversifications including the formal synthesis of nicotlactone B and galbacin.