The utility of intramolecular cycloadditions of ortho-quinodimethanes for the synthesis of complex polycyclic molecules is illustrated: 1) by the stereoselective synthesis of the natural alkaloid (±)-chelidonine starting from a benzocyclobutene; 2) by the efficient preparation of various polycyclic carbon skeletons using 1,3-dihydroisothianaphthen-2,2-dioxide as a simple building block. Furthermore, the total syntheses of the ergolines chanoclavine I and isochanoclavine I, exploiting a regio- and stereo-selective intramolecular nitrone-olefin-addition, is described.