Construction of poly-N-heterocyclic scaffolds via the controlled reactivity of Cu-allenylidene intermediates.

Controlling the sequence of the three consecutive reactive carbon centres of Cu-allenylidene remains a challenge. One of the impressive achievements in this area is the Cu-catalyzed annulation of 4-ethynyl benzoxazinanones, which are transformed into zwitterionic Cu-stabilized allenylidenes that are trapped by interceptors to provide the annulation products. In principle, the reaction proceeds via a preferential γ-attack, while annulation reactions via an α- or β-attack are infrequent. Herein, we describe a method for controlling the annulation mode, by the manipulation of a CF or CH substituent, to make it proceed via either a γ-attack or an α- or β-attack. The annulation of CF-substituted substrates with sulfamate-imines furnished densely functionalized N-heterocycles with excellent enantioselectivity via a cascade of an internal β-attack and an external α-attack. CH-variants were transformed into different heterocycles that possess a spiral skeleton, via a cascade of an internal β-attack and a hydride α-migration followed by a Diels-Alder reaction.