UC San Diego

This work is mainly composed of two parts. The first part talks about synthesis and reactivity studies of metallacyclobutenes (MCB) and 4-cobalt-cyclopentadienes derived therefrom, which includes chapter 1, 2, 3, and 4. The second part talks about ruthenium-mediated/catalyzed cyclizations of conjugated tri- molecules, which includes chapter 5, 6, 7, and 8.

Chapter 1 is a review of historical development of metallacyclobutenes and 4-cyclopentadienes with numerous literature-reported representative examples. Chapte 2 talks about preparation of new cobaltocyclobutenes, reversible thermolysis of MCB to dicobalt propendiyl complex, formation of 4-diene complexes from MCB, photochemical isomerization of MCB, and the reactivities of MCB/cobalt-alkyne complexes towards dizaoacetamide. Chapter 3 presents syntheses of 4-cyclopentadienes and vinylmetallacyclobutene complexes, as well as further reactivity study of 4-cyclopentadienes to produce highly functionalized cobaltocenium cations and arenes. Chapter 4 introduces a Brønsted acids triggered demetallation of 4-cyclopentadiene to give fulvenol, cyclopentenone, and cyclopentadienes as products.

Chapter 5 talks about an air-stable ruthenium-naphthalene complex Cp*Ru(Nap)PF6 as trigger of “Cp*Ru+” under photochemical conditions to cycloaromatize enediyne in the presence of 1,4-cyclohexandiene at ambient temperature. Chapter 6 describes a chemoseletive ruthenium-mediated cycloaromatization of dienynes with phenyl goup. A noval ruthenium-catalyzed cyclization mode was also discovered on a chlorine and methyl incorporated dienyne, whose regioselectivity is controlled by the size of a nearby fused ring. Chapter 7 is a clean-up work of an unprecedented cycloaromatization mode of enediynes. Both vinyl chloride intermediates and arene products were resynthesized from a modified method with higher yields, and products were furtherly purified and fully characterized. Mechanistic studies were carried out via deuterium labelling experiments. Chapter 8 introduces ruthenium-mediated/catalyzed conjugated trienes. The reactions of Cp*Ru(NCMe)3PF6 with trienes at ambient temperature give 6-arene complex with excellent yields. VT NMR experiments allows the observation and isolation of variable metal-triene intermediates at low temperature. Furthermore, the first example of metal-complexation catalyzed 6 electrocyclization of conjugated trienes was discovered.