Borrowing Hydrogen in the Synthesis of Alcohols and Amines

This thesis is concerned with the transformation of carbonyl compounds and allylic alcohols (and some amines) into alcohols via the process of transfer hydrogenation. The main work develops the idea of a new hydrogen donor for transfer hydrogenation and then applies it to an impressive one pot reaction. The transformation of amines shows an unexpected reaction and investigation into this reveals a possible mechanism for the reaction. Chapter 2: 1,4-Butanediol is introduced as a new hydrogen donor. It is used to convert a wide range of carbonyl substrates successfully into their alcohol counterparts after optimisation of conditions. A comparison with other straight chain alkanediols proves that 1,4-butanediol is the most suitable diol to use. The asymmetric aspect of the chemistry is investigated, but the results obtained do not compare to those already published in the literature. Chapter 3: A one pot reaction of isomerisation and reduction of allylic alcohols is proposed and proven. This is achieved by using 1,4-butanediol as the solvent and hydrogen donor. A wide range of allylic alcohols are converted to their corresponding saturated alcohols. The conditions were not applicable to asymmetric results. Chapter 4: The reaction of straight chain alkanediols with themselves is discovered and investigated to find they produce cyclic acetals. Results vary depending on the length of the alkyl chain. A series of experiments improved initial results to complete conversion. However isolation of these compounds remains a problem and requires more work. Chapter 5: During the synthesis of Diphenhydramine, an unexpected rearrangement reaction was discovered. This reaction was found to be specific to a certain structural arrangement on the compound. Investigations using 13C labelling found a plausible mechanism to explain the reaction.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Reduction of aldehydes and ketones by transfer hydrogenation with 1,4-butanediol

[GRAPHICS] 1,4-Butanediol has been used as the hydrogen donor in transfer hydrogenation reactions. The equilibrium is driven by the formation of gamma-butyrolactone, and the diol is therefore not required in excess

1,4-Butanediol as a Reducing Agent in Transfer Hydrogenation Reactions

1,4-Butanediol is able to deliver two equivalents of H(2) in hydrogen-transfer reactions to ketones, imines, and alkenes. Unlike simple alcohols, which establish equilibrium in the reduction of ketones, 1,4-butanediol acts essentially irreversibly owing to the formation of butyrolactone, which acts as a thermodynamic sink. It is therefore not necessary to use 1,4-butanediol in great excess in order to achieve reduction reactions. In addition, allylic alcohols are reduced to saturated alcohols through an isomerization/reduction sequence using a ruthenium catalyst with 1,4-butanediol as the reducing agent. Imines and alkenes are also reduced under similar conditions

Ruthenium-Catalyzed N-Alkylation of Amines and Sulfonamides Using Borrowing Hydrogen Methodology

The alkylation of amines by alcohols has been achieved using 0.5 mol % [Ru(p-cymene)Cl(2)](2) with the bidentate phosphines dppf or DPEphos as the catalyst. Primary amines have been converted into secondary amines, and secondary amines into tertiary amines, including the syntheses of Piribedil, Tripelennamine, and Chlorpheniramine. N-Heterocyclization reactions of primary amines are reported, as well as alkylation reactions of primary sulfonamides. Secondary alcohols require more forcing conditions than primary alcohols but are still effective alkylating agents in the presence of this catalyst