Alan Armstrong

Exocyclic iminium salts as catalysts for alkene epoxidation by Oxone

Abstract Exocyclic iminium salts are evaluated as catalysts for alkene epoxidation by Oxone ® , presumed to proceed via the corresponding oxaziridinium species. Iminium triflate salts derived from pyrrolidine and electron poor aromatic aldehydes were found to be good catalysts. Attempts to prepare chiral variants of these iminium salts were largely unsuccessful, presumably due to their ready hydrolysis.

Alkene epoxidation catalyzed by bicyclo[3.2.1]octan-3-ones: effects of structural modifications on catalyst efficiency and epoxidation enantioselectivity

Abstract Several 2-substituted bicyclo[3.2.1]octan-3-ones are prepared and have been tested as catalysts for alkene epoxidation by Oxone ® .

Electrophilic amination of carbanions by N-carboxamido oxaziridines

A range of 3-aryl-N-carboxamido oxaziridines have been prepared and tested as reagents for electrophilic amination of carbanions. The 3-(2-cyanophenyl)-derivative gave highest yields of amination product, and was used for amination of ketone, ester and amide enolates, as well as sulfone-, phosphonate- and nitrile-stabilized carbanions.

α-Functionalised ketones as promoters of alkene epoxidation by Oxone®

Abstract Acceleration of Oxone® epoxidation of alkenes by several α-functionalised ketones, including α-amido ketones, is investigated. In general, competing decomposition by Baeyer-Villiger reaction prevents use of the ketones as efficient epoxidation promoters. However, a novel oxazolidinone-derived ketone provides epoxides with moderate enantioselectivity (up to 34% ee).

Concise synthesis of (4S,5S)-4,5-(isopropylidenedioxy)-2-cyclopentenone and a novel C2-symmetric ketone

Abstract A new and concise synthesis of the useful synthetic intermediate 1 is described which also allows access to a novel C 2 -symmetric keton 2 . The route relies on the Sharpless asymmetric dihydroxylation of fulvenes.

Highly stereoselective intramolecular epoxidation in unsaturated oxaziridines

Highly stereoselective intramolecular epoxidation is observed in unsaturated oxaziridines via oxaziridinium salts. The observed selectivities are consistent with a spiro transition state for the intramolecular epoxidation.

Catalytic enantioselective epoxidation of alkenes with a tropinone-derived chiral ketone

α-Fluoro-N-ethoxycarbonyltropinone is an efficient catalyst for the epoxidation of alkenes by Oxone® with good enantioselectivity.

Intramolecular epoxidation in unsaturated ketones and oxaziridines

The possibility of intramolecular epoxidation in acyclic unsaturated ketones (via dioxiranes) and oxaziridines (via oxaziridinium species) has been investigated. Treatment of several acyclic unsaturated ketones with Oxone® led to low levels of regio- and stereocontrol, suggesting that background epoxidation by Oxone® dominates. However, treatment of unsaturated oxaziridines with methyl trifluoromethanesulfonate led to intramolecular epoxidation. This process allowed regioselective epoxidation of a non-conjugated diene. It also proceeded with a high degree of stereocontrol consistent with a stereoelectronic preference for a spiro-transition state.