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Diolefin metathesis, using a Re2O7 catalyst, failed to show a reactivity difference due to conjugation of double bonds. However, the same system allows reaction of pentadiene while not affecting cyclopentene yielding a successful reaction ΓÇô separation scheme for a piperylene concentrate mixture.

This report discusses research which was conducted in two areas: the study of aromatic nucleophilic fluoroalkoxylation assisted via cationic phase transfer catalysis and the study of unsymmetrical vinamidinium salts and their reactions with organometallic reagents. Sodium alkoxides have been successfully used to fluoroalkoxylate activated halo- aryl and heteroaryl substrates under phase transfer catalysis conditions. Optimum reaction conditions incorporated tetra-n-butyl-phosphonium bromide as the catalyst and refluxing toluene as the solvent medium. Different quarternary phosphonium and arrmonium salts have been evaluated as catalysts: also, the effects of activating groups, leaving groups, and nucleophiles have been reported. The reaction of 3-dimethylamino-3-phenyl-prop-2-en-l-ylidendimethyliminium perchlorate with organolithium and Grignard reagents has also been studied in an effort to define the reaction in terms of which electrophilic site of the salt is susceptible to nucleophilic attack to the greatest extent. The results reported reveal that the reaction occurs at the 1-position in all cases producing the α, β-unsaturated ketone after acid hydrolysis. Finally, this report reveals the experimental procedures used as well as the spectral and physical data of all new compounds synthesized. Explanations of the data are offered and recommendations for future research in both areas are given.

Thesis advisor: James P. Morken / This dissertation will present three main projects focusing on the transition metal-catalyzed enantioselective synthesis of secondary organoboronic esters and progress towards the total synthesis of sarcodictyins. In the first project, a palladium-catalyzed enantioselective conjunctive cross-coupling reaction with propargylic electrophiles will be described. The tetra-substituted allenes are isolated with good yield and enantioselectivity and the beneficial effects of alcohol additives are investigated. The second project describes the enantioselective synthesis of ɑ-boryl zinc reagents by a nickel-catalyzed carbozincation reaction. The in situ generated ɑ-boryl zinc intermediate can be trapped by copper-mediated allylations, palladium-catalyzed Negishi cross-couplings, and cerium-mediated halogenation reactions to construct various chiral organoboranes. The synthetic utility of this methodology is showcased by the synthesis of natural products, including bruguierol A, (-)-aphanorphine, and (-)-enterolactone. The mechanism is studied with the assistance of EPR and deuterium-labeling experiments and a catalytic cycle through a Ni(I) intermediate is proposed. The third project depicts a synthetic route to essential precursors in the progress of the total synthesis of sarcodictyins. Various attempts to construct the ten-membered ring core of sarcodictyin have been made, including Sonogashira reaction, Dieckmann condensation, and lithium—halogen exchange process. / Thesis (PhD) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

This thesis presented the synthesis and reactivity of metal complexes for the hydrophosphination of alkenes and dehydrocoupling of phosphines. The mechanism of these metal-catalyzed P-H activation reactions was explored. Half-sandwich Cp*Ru complexes (Cp*= 1,2,3,4,5-pentamethylcyclopentadienyl) were developed as catalysts for hydrophosphination, based on the previous work in the Rosenberg group. Cp*Ru phosphido complexes, Ru(h 5 -Cp*)(PR2 )(PR2 H)2 (Ru-1) were found to be the vital intermediates for the hydrophosphination. Preliminary mechanistic studies also indicate that the catalyst resting state is Ru(h5 -Cp*)(PR2 )(PR2 H)(P) (P = hydrophosphination product) and intramolecular P-H bond cleavage is turnover-limiting. These investigations provide sufficient parallels to our established chemistry of the indenyl analogues to imply that conjugate addition of metal phosphido at alkene plays a significant role in these half-sandwich catalytic systems. The increased steric crowding at the Cp*Ru fragment and P-basicity/nucleophilicity of its phosphido complexes lead to a 30-fold increase in the hydrophosphination activity in the Cp* system compared to the indenyl catalysts. A half-sandwich Co catalyst, Co(h 5 -Cp*)I 2 (CO) (Co-1), was also developed for hydrophosphination along the lines of the conjugate addition mechanism. Similar to the Cp*Ru system, the substrate scope for alkene is limited to electron-deficient alkene. However, the Cp*Co catalyst significantly expands the substrate scope for phosphines (PR2 H and PRH 2 , R = alkyl and aryl). A detailed mechanistic study on the Cp*Co system was performed. The results show that the Co-catalyzed hydrophosphination occurs through iv an outer-sphere mechanism and the stoichiometric formation of diphosphine is a critical catalyst activation step. Since the side product diphosphine was formed during the Co-catalyzed hydrophosphination, using complex Co-1 as a catalyst for dehydrocoupling phosphines was investigated. The preliminary studies reveal the role of base and Cp* ligand in the catalysis. Additionally, the study highlights the importance of removing dihydrogen throughout the process. Thus, hydrogen acceptors (HA) were used to facilitate the dehydrocoupling reactions. Last, the novel P-H activation process between Cp*Co complexes [Co(h5 -Cp*)(NCCH 3 ) 3 ][SbF 6 ] 2 (Co-5) and excess PPh2 H was investigated through various analytical techniques. / Graduate / 2023-09-08