Adventures with acetylenes: A personal odyssey from Wyerone and Crepenynic Acid to enediynes, acetylenic cyclophanes, and propargyl alcohols

This account provides an overview, in varying depth, of our research into diverse aspects of acetylene chemistry over the last three decades. Initial studies with acetylenic natural products (Wyerone, Crepenynic Acid) were followed several years later with synthetically oriented projects. These involved enediyne mimics of natural products (Taxamycins) and unusual selenium dioxide oxidations of alpha-alkynyl ethers. Helical acetylenic cyclophanes (Revolvenynes) were synthesized by sequential palladium- and copper-mediated reactions, which set the precedent for later research. Related cyclophanes as potential intermediates for buckminsterfullerene (C60) are discussed. Helical carbocyclic liquid crystalline and heterocyclic (copper-free and complexed) cyclophanes were also prepared. A very strained 153.5degrees triple bond was discovered which reacted with cyclohexadiene to form the bicyclic adduct in situ and extruded ethylene to generate a new cyclophane with an annulated benzene ring attached. In situ desilylation-dimerization sequences are described and a table is presented for guidance to predict the preferred product from competing intra- and intermolecular copper-mediated coupling pathways. The synthetic details for two different helical, pi-stacked C60 cyclophane families with para and meta bonded caps and different structural motifs are presented (Scheme 13 and Scheme 14) for comparison with Scheme 1. These concepts are being extended to the synthesis of allenocyclophanes. A brief discussion of a pi-extended boron-azulene complex is followed by a summary of magnesium-mediated carbometallations of propargyl alcohols. A final comment reexamines our cyclophane-based approach to buckminsterfullerene.