Benjamin R. Buckley

Experimental Evidence for the Involvement of Dinuclear Alkynylcopper(I) Complexes in Alkyne–Azide Chemistry

Dinuclear alkynylcopper(I) ladderane complexes are prepared by a robust and simple protocol involving the reduction of Cu(2)(OH)(3)OAc or Cu(OAc)(2) by easily oxidised alcohols in the presence of terminal alkynes; they function as efficient catalysts in copper-catalysed alkyne-azide cycloaddition reactions as predicted by the Ahlquist-Fokin calculations. The same copper(I) catalysts are formed during reactions by using the Sharpless-Fokin protocol. The experimental results also provide evidence that sodium ascorbate functions as a base to deprotonate terminal alkynes and additionally give a convincing alternative explanation for the fact that the Cu(I)-catalysed reactions of certain 1,3-diazides with phenylacetylene give bis(triazoles) as the major products. The same dinuclear alkynylcopper(I) complexes also function as catalysts in cycloaddition reactions of azides with 1-iodoalkynes.

Alkynylcopper(I) polymers and their use in a mechanistic study of alkyne–azide click reactions

Polymeric dinuclear alkynylcopper(I) complexes, for example phenylethynylcopper(I), can be prepared by a robust method involving the interaction of terminal alkynes with copper(II) salts in acetonitrile. The use of the ladder polymers provides heterogeneous catalysts for copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions and provides important mechanistic information.

Electrosynthesis of cyclic carbonates from epoxides and atmospheric pressure carbon dioxide

The use of CO(2) for the preparation of value-added compounds has dramatically increased due to increased global warming concerns. We herein report an electrochemical cell containing a copper cathode and a magnesium anode that effectively converts epoxides and carbon dioxide to cyclic carbonates under mild electrochemical conditions at atmospheric pressure.

Asymmetric Epoxidation Using Iminium Salt Organocatalysts Featuring Dynamically Controlled Atropoisomerism

Introduction of a pseudoaxial substituent at a stereogenic center adjacent to the nitrogen atom in binaphthyl- and biphenyl-derived azepinium salt organocatalysts affords improved enantioselectivities and yields in the epoxidation of unfunctionalized alkenes. In the biphenyl-derived catalysts, the atropoisomerism at the biphenyl axis is controlled by the interaction of this substituent with the chiral substituent at nitrogen.

Mannich reactions of alkynes: mechanistic insights and the role of sub-stoichiometric amounts of alkynylcopper(I) compounds in the catalytic cycle.

Yellow polymeric alkynylcopper(I) compounds observed in the three-component Mannich reactions of alkynes, secondary amines and aldehydes are shown to be pre-catalysts that give rise to catalytic copper(I) alkyne complexes by interaction with secondary amines (see scheme). Interaction of these complexes with iminium ions (formed from aldehydes or their equivalents, including CH2Cl2), results in the formation of Mannich bases in high yields.

Mechanistic Investigations of Copper(I)-Catalysed Alkyne–Azide Cycloaddition Reactions

The chapter concentrates on mechanistic aspects of thermal and metal catalysed reactions of organic azides and alkynes, particularly terminal alkynes, that result in the formation of 1,2,3-triazoles.

Kinetic Resolution in Asymmetric Epoxidation using Iminium Salt Catalysis

The first reported examples of kinetic resolution in epoxidation reactions using iminium salt catalysis are described, providing up to 99% ee in the epoxidation of racemic cis-chromenes.

Selective Formation of Trimethylene Carbonate (TMC): Atmospheric Pressure Carbon Dioxide Utilization

Carbon dioxide utilisation (CDU) is currently gaining increased interest due to the abundance of CO2 and its possible application as a C1 building block. We herein report the first example of atmospheric pressure carbon dioxide incorporation into oxetane to selectively form trimethylene carbonate (TMC), which is a significant challenge as TMC is thermodynamically less favoured than its corresponding co-polymer.

Atropo- and Diastereoselective Construction of Tetracyclic Biphenylazepinium Salts Derived from Aminoalcohols: Use as Catalysts in Enantioselective Asymmetric Epoxidation

A range of new biphenylazepinium salt organocatalysts effective for asymmetric epoxidation has been developed incorporating an additional substituted oxazolidine ring, and providing improved enantiocontrol in alkene epoxidation over the parent structure. Starting from enantiomerically pure aminoalcohols, tetracyclic iminium salts were obtained as single diastereoisomers through an atroposelective oxazolidine formation.

Carboxylic Esters and Lactones

There are an extremely large number of procedures for the synthesis of carboxylic esters and lactones. This review attempts to summarize some of the more useful techniques. For example, esters can be prepared by direct esterification using a carboxylic acid and an alcohol. The synthesis of lactones can be achieved using many of the procedures used in the formation of carboxylic esters. One of the most useful techniques for lactone synthesis is macrolactonization, and a large number of natural products have been synthesized using this approach.