Self-Addition of a Sterically Hindered Alkynylselenolate

[structure: see text] The unprecedented formation of a complex macrocyclic selenium-carbon ring system, which is initiated by the action of coordinating reagents upon a sterically hindered alkynylselenolate, has been observed. The crystal structure of the product could be obtained and shows a rigid tricyclic arrangement consisting only of selenium and sp(2)-hybridized carbon atoms. This reactivity stands in contrast to the corresponding unsubstituted alkynylselenolates and is an example where a bulky substituent destabilizes an adjacent unsaturated pi-system.