The syntheses of sterically stabilized cyclopropenonophanes as well as an electronically stabilized cyclopropenethionophane are reported, and their molecular structures in the solid state are elucidated. The sulfur of the CS moiety in cyclopropenethiones was shown to react as a nucleophile. Temperatures of more than 240 degrees C favor the extrusion of CO in the cyclopropenonophane to afford an alpha,alpha'-tetramethyl-substituted cyclodiyne. [reaction: see text]