Iridium Catalyzed Regioselective Allylic Alkylation And Hydrogen Transfer Reaction

In the past few years,research on the iridium catalysis has been increasingly reported.In some processes,iridium complexes may be more effective and selective than other transition metals.In this dissertation,reviews aiming at the development of iridium-catalyzed C-C bond formation and dehydrogenation of alcohols were summarized first.And on this basis,several novel catalytic methodologies about the iridium-catalyzed regioselective allylic alkylation and hydrogen transfer reaction based on alcohols were described in detail.First,the iridium-catalyzed allylic alkylation using allylic alcohols as allyl source was explored.(1)In the presence of a catalytic amount of H2SO4,allylic alcohol could be activated and participated in the allylic alkylation as an allyl source with the[Ir(cod)Cl]2.In the case of monosubstituted allylic alcohols,the allylic alkylation selectively occured at the C-3 position of indoles,affording the branched products in branched-linear ratio of up to 99/1.(2)Furthermore,the C-nucleophile was extended to the ?-ketoacids after a screening on acids.An iridium-catalyzed regioselective decarboxylative allylic alkylation of ?-ketoacids with allylic alcohols was developed,affording a series of ?,?-unsaturated ketones.A study on the mechanism indicated that the carbon-carbon bond formation preceded the decarboxylation.Compared with the conventional alkaline methyl ketone enolate,the ?-ketoacids could resist a second allylation with another allylic substrate.The methodology represented an atom-and step-economical synthesis that directly used allylic alcohols as substrates without prior activation such as esterification or halogenation.Furthermore,the simplicity of the system using commercially available catalyst without an additional ligand made it easy-to-use.Next,iridium-catalyzed transfer hydrogenation using alcohols as hydrogen donor was investigated in the thesis.(1)A simple catalytic system composed of[Cp*IrCl2]2 and K2CO3 was developed for the 1,4-reduction of ?,?-unsaturated ketones using isopropanol as hydrogen donor,affording the saturated ketones with yield up to 98%.While switching the base from K2CO3 to KOH,the generated ?,?-unsaturated ketones could be further reduced to saturated alcohols.(2)An attempt to reduce the nitroarenes to anilines using the above system resulted in only moderate yield and selectivity.Further screenings demonstrated that[Ir(cod)Cl]2/1,10-phenanthroline/KOH was an efficient catalytic system for the transfer hydrogenation of nitroarenes to anilines with isopropanol.Compared with hydrogen gas,silanes and other metallic reductants,isopropanol was an attractive hydrogen donor due to its good solvent properties,being less expensive,and no need of special hydrogenation reactor.(3)Then,an intramolecular transfer hydrogenation of ally lic alcohols was also investigated.It was found that[Cp*IrCl2]2 was an efficient catalyst for the isomerization of allylic alcohols to ketones.This was a redox-neutral reaction possessing 100%atom economy.Based on this,a new tandem catalytic process composed of isomerization and oxidative cyclization was established for the synthesis of substituted quinolones from allylic alcohols and 2-aminobenzyl alcohol.Finally,the iridium-catalyzed methylation using methanol as methylating agent was studied.Through the control of reaction conditions,an iridium-catalyzed methodology was developed for the methylation of indoles and pyrroles using methanol as methylating agent.The coupling followed a catalytic cycle including oxidation,nucleophilic addition,dehydration and reduction.Methanol was an ideal methylating agent which was vastly abundant,cheap and renewable.And again,the simplicity of the system using commercially available[Cp*IrCl2]2 without an additional ligand made it readily accessible.