Martyn Frederickson

X=Y-ZH systems as potential 1,3-dipoles. Part 47.1 tandem nucleophilic substitution-1,3 dipolar cycloaddition reactions of oximes with epoxides and dipolarophiles

Abstract Regiospecific nucleophilic substitution reactions involving attack of the nitrogen atom of oximes on epoxides are used to generate nitrones which are then trapped in 1,3-dipolar cycloaddition reactions. These tandem processes are shown to be flexible and to have wide synthetic scope for the construction of complex molecular frameworks.

X=Y-ZH systems as potential 1,3-dipoles. Part 49. Catalytic palladium (II) mediated oxime-nitrone-isoxazolidine cascades

Abstract Bis(acetonitrile) palladium (II) chloride (10 mol %) effects cyclization of δ-alkenyl oximes to nitrones which undergo in situ 1,3-dipolar cycloaddition reactions with suitable dipolarophiles to afford a range of complex isoxazolidine derived heterocycles in high yield (81–85%).

Palladium (II) catalysed oxime-metallo-nitrone-isoxazolidine cascade reactions of α-imino aldoximes

Abstract Palladium (II) salts catalyse stereospecific and highly facially selective oxime-nitrone-isoxazolidine cascade reactions between α-imino aldoximes and N -methylmaleimide via intermediate N -metallo-aldonitrones. These processes occur at room temperature in a range of polar solvents through the chelation of both α-imino and aldoxime nitrogen atoms to the palladium (II) centre.

X=Y-ZH systems as potential 1,3-dipoles. Part 48. Enantiopure cycloadducts from oxime-nitrone-isoxazolidine cascades ☆

Abstract Enantiopure cycloadducts have been prepared in good yield via oxime-nitrone-isoxazolidine cascade reactions involving the nucleophilic opening of enantiopure epoxides with oximes followed by 1,3-dipolar cycloaddition reactions with suitable dipolarophiles.

Homochiral cycloadducts derived from sugar aldoximes via nitrone intermediates

Abstract Tandem nitrone generation/cycloaddition reactions between simple sugar aldoximes and divinyl sulphone in refluxing toluene have been shown to occur regiospecifically and with high diastereoselectivity in the cycloaddition step to afford homochiral cycloadducts in good yield. The process is applicable to both furanose and pyranose aldoximes. Absolute stereochemistries of the products have been determined by NOE spectroscopy and X-ray crystallography.

On the absolute stereochemistries of homochiral cycloadducts derived from oxygenated aldoximes and divinyl sulphone via azaprotio cyclotransfer

Abstract Further studies into the regiospecific tandem nitrone generation/cycloaddition reaction between chiral oxygenated aldoximes and divinyl sulphone have shown that cycloaddition diastereoselectivity can be controlled by a single stereogenic centre located α- to the oxime moiety. Diastereoselectivity is greatly enhanced when the α-stereocentre constitutes part of a ring system and the absolute stereochemistry of the major cycloadduct can be accurately predicted based upon the absolute stereochemistry at the α-centre of the oxime.

Tandem 1,3-azaprotio cyclotransfer-cycloaddition reactions between ketoximes and divinyl ketone or its equivalents: Lewis acid mediated rate enhancement and control of cycloaddition regioselectivity

Abstract The tandem 1,3-azaprotio cyclotransfer-cycloaddition reaction between a ketoxime and divinyl ketone or its equivalents [2-chloroethyl vinyl ketone and bis(2-chloroethyl) ketone] affords high yields of substituted 1-aza-7-oxabicyclo[3.2.1]octan-4-ones and 1-aza-8-oxabicylo[3.2.1]octan-4-ones. Addition of zinc bromide results both in rate enhancement and control of cycloaddition regioselectivity affording almost exclusively 1-aza-7-oxabicyclo[3.2.1]octan-4-ones.

Palladium(II)-catalysed cascade cyclisation–cycloaddition reactions of alkenyl oximes

Palladium(II) chloride-catalysed cascade cyclisation–cycloaddition reactions of δ-alkenyl oximes occur regio- and facially-specifically in high yield via intermediate six-membered cyclic nitrones; preliminary studies of γ-alkenyl oximes show they are reluctant to cyclise; four potential synthetic variants of the cascade process are identified and examples of two of the classes are provided.