Abstract
Chapter I In this chapter, we report a new ruthenium-catalyzed 6-endo-dig cyclization of 6,6-cycloalkylidenyl-3,5-dien-1-ynes, which produces highly substituted benzenes with considerable structural reorganization. In this process, we observe a regioselective 1,3-methylene migration via extrusion from a cycloalkylidenyl ring, in addition to a regiocontrolled 1,2-alkyl migration. This cyclization provides an easy and convenient synthesis of complex benzenes bearing various distinct substituents. Chapter II describes the feasibility of thermal and catalytic cyclization of 6,6-disubstituted 3,5-dien-1-ynes via a 1,7-hydrogen shift. We first studied the thermal efficiency of model molecules via alternation of the C(1)-phenyl and C(6)-carbonyl substituents of substrates; we concluded that the observed 1,7-hydrogen shift is nearly a “protonic” hydrogen shift. This structure-activity relationship indicates that π-alkyne activators can catalyze suitably functionalized 3,5-dien-1-ynes efficiently although their thermal yields were generally low. We prepared various 6,6-disubstituted 3,5-dien-1-ynes bearing either a phenyl or carbonyl group, and found their thermal cyclizations to be greatly enhanced by RuCl3, PtCl2, TpRuPPh3(CH3CN)2PF6 catalysts to confirm our hypothesis: the C(7)-H acidity of 3,5-dien-1-ynes is crucial for thermal cyclization. To achieve the atom economy, we have developed a tandem aldol condensation-dehydration and aromatization catalysis between cycloalkanones and special 3-en-1-yn-5-als using the weakly acidic catalyst CpRu(PPh3)2Cl, which provided complex 1-indanones and α-tetralones with yields exceeding 65% in most cases. In chapter III, we report a new efficient intramolecular [3+2]-cycloaddition of unactivated arenyne (or enyne)-yne function-nalities, catalyzed mainly by AuPPh3SbF6 complex under ambient conditions. The value of this cyclization is reflected by its applicability to a wide range of diyne substrates bearing various functional groups. In chapter IV, we report a new efficient gold-catalyzed cyclization of 1,6-diyne-4-en-3-ol and 1,6-diyne-4-en-3-methoxy derivatives to give naphthyl ketone derivatives under ambient conditions. The cyclization is proposed to proceed via a vinylgold carbocation species, which subsequently triggers the cyclization via a 6-endo-dig attack of the allene group or intramolecular cycloadditon. The value of this cyclization is reflected by its applicability to a wide range of alcohol and methoxy substrates bearing various functional groups.