Alternatively, we considered an intermolecular Diels-Alder approach, in which a tryptamine derivative 1 would undergo direct cycloaddition with TDO 6 to form adduct 7. 6 would necessarily feature a disposable substituent ('X') that is essential to prevent heterodimerisation of the thiophene S-monoxide with S,S-dioxide 6 in the course of its oxidative synthesis . Subsequent to the cycloaddition / cheletropic extrusion cascade, cyclisation of the tryptamine sidechain, cleavage of the now superfluous substituent 'X', and N-alkylation with 2 would afford the same advanced intermediate 5. Here we describe the development of these two strategies, culminating in a collective asymmetric synthesis of eight natural products in the Strychnos family. In doing so, we also establish the first asymmetric intermolecular cycloadditions of TDOs, accessing tricyclic indoline scaffolds that are of potential utility for medicinal chemistry applications. We further use computational studies to reveal the source of the exquisite stereoselectivity observed in the IEDDA reaction, which also suggest that these TDO cycloadditions benefit from an entropic driving force where cheletropic extrusion of SO2 occurs spontaneously along the cycloaddition pathway, without formation of an intermediate cycloadduct.