Dual Gold Catalysis: Bidirectional Processes and Tandem sp³ -C-H Insertion Reactions

Various tetrayne systems were converted under dual gold-catalyzed conditions. For symmetric tetraalkynyl-substituted thiophenes, bearing two alkyl-substituted alkynes and two terminal alkyne units, bidirectional cyclizations led to the efficient formation of dibenzothiophene systems. In all cases, selective CH activation of the C-H bond of the alkyl substituent was observed leading to cyclopentane moieties annelated to the newly formed aromatic cores. If two thiophene moieties were tethered over the attached non-terminal alkynes, depending on the length of the connecting alkyl tether, either bidirectional processes or tandem processes can be addressed leading to interesting molecular structures, such as spiro compounds or isolated benzothiophenes connected by a C-C bond. Other electron-rich heterocycles also reacted. While the reactions even worked for some mixed systems, other cases only delivered the products of a mono-cyclization.