Ring Expansion of Tetrahydroisoquinolines to Form Benzoazocines

Significance

Reported is a synthesis of azocines from tetrahydroisoquinolines by ring expansion using an activated alkyne. A mechanism is proposed which involves initial formation of a zwitter­ion species (structure A above) by Michael addition of the tertiary amine to an alkyne, followed by a mechanistically unknown rearrangement to afford the azocine.