Date of Award
Chemistry and Biochemistry
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The Nazarov cyclization reaction has been used as an effective method to synthesize cyclopentanones. While 6-membered ring systems can be available by way of the homo Nazarov variant, 7-membered ring formation involving a Nazarov-type reaction is very rare, and completely unknown thermally. Using the established concept of the ability of the alkyne-Co2(CO)6 moiety to enable the formation of -carbonyl cations and the good stability of this generated cation, 7-membered ring formation via the vinylogous Nazarov reaction with electron deficient enones has been investigated. The desired aryl substituted enyone-Co2(CO)6 complex precursors for the cyclization reaction have been prepared from commercially available starting materials, using a series of reactions that include Sonogashira cross-coupling, desilylation, organolithium reactions with aldehydes, oxidation and complexation reactions. The treatment of the respective complex precursors, using SnCl4 as a suitable Lewis acid, successfully generated cycloheptynone-Co2(CO)6 complexes. The substitution effects have been examined, showing that introducing a bulky group at the alpha-position to the carbonyl enhances the cyclization efficiency by enabling the desired s-trans/s-trans conformation. On the other hand, beta-substituting with an R group other than H atom reduces the reaction rate and allows formation of the desired 7-membered ring only in very low yield. Preparation of appropriate dienynone-Co2(CO)6 complex substrates allowed expansion of the reaction scope to non-aromatic starting materials. Successful reductive decomplexation of the cycloheptynone-Co2(CO)6 unit also was demonstrated.
Almubayedh, Somaiah Khalid, "Metal-Mediated Vinylogous Nazarov Cyclization Reaction" (2019). Electronic Theses and Dissertations. 7798.