Thesis

Mediated electrohydrocyclization reactions with heterogeneous metal catalysts

Organic electrochemistry has become a useful and environmentally friendly alternative to
 traditional organic synthesis. Electrochemistry provides a tool with which electrons can be
 selectively introduced or removed from an organic molecule, allowing for the reversal of
 functional group polarity. This allows for the coupling of two electrophiles or two
 nucleophiles in ways that would otherwise be impossible to accomplish. The
 electrohydrocyclization (EHC) and elecroreductive cyclization (ERC) reactions to form
 carbocyclic rings have been used as the key step in the synthesis of several anti-cancer
 compounds and natural products. The direct, unmediated EHC was first discovered by
 Baizer in the 1960’s and then developed into the mediated EHC reaction by Miranda,
 Wade, and Little in the early 2000’s. Metal-salen compounds can serve as excellent
 electrochemical mediators in these reactions, resulting in a chemoselective process due to
 the reaction being run at a more positive potential than unmediated reactions. In addition,
 since only a catalytic amount of mediator is needed, the resultant chemical waste is greatly
 reduced, resulting in a more environmentally friendly reaction. This thesis develops upon
 the unmediated and mediated EHC reaction by exercising a new class of heterogeneous 
 v
 electrocatalysts to mediate the EHC reaction while remaining in the solid phase.
 Specifically, this research developed two types of solid-supported catalysts. Two
 approaches were studied: anchoring the electrocatalyst to a solid-phase polymer
 (Merrifield resin) and encapsulation of Ni(salen) in porous zeolite Y. The primary benefit
 of a heterogeneous catalyst is the drastic improvement of reaction work-up and
 purification. Furthermore the heterogeneous catalysts can be washed and re-used. The EHC
 reaction was performed with several heterogeneous and homogeneous catalysts to allow
 for comparison. The cis/trans ratio results from each reaction did not show drastic
 differences between each catalyst. The EHC reaction with the heterogeneous catalyst
 resulted in higher yields over the homogeneous catalysts.

Thesis (M.S., Chemistry)--California State University, Sacramento, 2018.

Organic electrochemistry has become a useful and environmentally friendly alternative to traditional organic synthesis. Electrochemistry provides a tool with which electrons can be selectively introduced or removed from an organic molecule, allowing for the reversal of functional group polarity. This allows for the coupling of two electrophiles or two nucleophiles in ways that would otherwise be impossible to accomplish. The electrohydrocyclization (EHC) and elecroreductive cyclization (ERC) reactions to form carbocyclic rings have been used as the key step in the synthesis of several anti-cancer compounds and natural products. The direct, unmediated EHC was first discovered by Baizer in the 1960’s and then developed into the mediated EHC reaction by Miranda, Wade, and Little in the early 2000’s. Metal-salen compounds can serve as excellent electrochemical mediators in these reactions, resulting in a chemoselective process due to the reaction being run at a more positive potential than unmediated reactions. In addition, since only a catalytic amount of mediator is needed, the resultant chemical waste is greatly reduced, resulting in a more environmentally friendly reaction. This thesis develops upon the unmediated and mediated EHC reaction by exercising a new class of heterogeneous v electrocatalysts to mediate the EHC reaction while remaining in the solid phase. Specifically, this research developed two types of solid-supported catalysts. Two approaches were studied: anchoring the electrocatalyst to a solid-phase polymer (Merrifield resin) and encapsulation of Ni(salen) in porous zeolite Y. The primary benefit of a heterogeneous catalyst is the drastic improvement of reaction work-up and purification. Furthermore the heterogeneous catalysts can be washed and re-used. The EHC reaction was performed with several heterogeneous and homogeneous catalysts to allow for comparison. The cis/trans ratio results from each reaction did not show drastic differences between each catalyst. The EHC reaction with the heterogeneous catalyst resulted in higher yields over the homogeneous catalysts.

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