The gold (I)-catatyzed cycloisomerization of 1,5-enynes and 1,4-allylallenes to tetracyclododecane and tetracyclotridecane derivatives, respectively, is reported. Complexation of the cationic gold(I) complex to either the alkyne or allene moiety induces an intramolecular addition of the alkene, leading to a gold(I)-stabilized carbenoid intermediate. This intermediate undergoes a format sp(3) C-H insertion to generate the tetracyclic adduct. A series of deuterium labeling experiments showed that the C-H functionalization step proceeds with an inverse kinetic isotope effect.