Jasothara Markandu

X = Y - ZH systems as potential 1,3-dipoles part 35. Generation of nitrones from oximes. Class 3 processes. Tandem intramolecular michael addition (1,3-azaprotio cyclotransfer) - intermolecular 1,3-dipolar cycloaddition reactions.☆☆☆

Abstract Aldoximes and ketoximes possessing γ- or δ-alkenyl substituents undergo thermal conversion to 5- and 6- membered cyclic nitrones via a 1,3-azaprotio cyclotransfer, a 2n + 2σ + 2π concerted process, rather than a Michael addition. The reactions can be performed as a tandem nitrone formation-cycloaddition sequence or, if required, the intermediate nitrones can be isolated. The cycloadditions usually proceed via an exo-transition state and show both regio- and diastereofacial-specificity. Preliminary attempts at chiral induction via a menthyl auxiliary are reported.

X=Y-ZH systems as potential 1,3-dipoles. Part 31. Generation of nitrones from oximes. Background and scope of the tandem 1,2-prototropy-intramolecular cycloaddition sequence.

Abstract 1,2-Prototropy in aryl and aliphatic oximes generates a small equilibrium concentration of the corresponding NH nitrone. Examples of a tandem 1,2-prototropy-intramolecular cydoaddition sequence involving aryl and aliphatic oximes are described and steric and electronic factors that favour or disfavour such a sequence are discussed. Deuterium labelling studies with an aliphatic oxime rule out the involvement of an enehydroxylamine in the prototropic generation of the NH nitrone.

X = Y - ZH Systems as potential 1,3-dipoles. Part 37 generation of nitrones from oximes. Tandem intramolecular 1,3-azaprotio cyclotransfer - intramolecular 1,3-dipolar cycloaddition reactions. Class 4 processes.

Abstract Aldoximes and ketoximes containing two alkenyl moieties in different side chains undergo thermal conversion to 5 - and 6 - membered cyclic nitrones, via concerted 1,3 - azaprotio cyclotransfer, followed by stereospecific intramolecular cycloaddition to give tricyclic spiro- and fused- ring systems. An X-ray crystal structure of one such product is reported.

XY–ZH Systems as potential 1,3-dipoles. Part 51: Halogen-induced inter- and intra-molecular formation of nitrones from oximes and alkenes

Abstract Oximes possessing γ- and δ-alkenyl substituents are cyclised by N-bromo- or N-iodosuccinimide, iodine or ICl to the corresponding cyclic nitrones or their dimeric H-bonded hydroiodide salts in good yield; facially specific cycloaddition of these nitrones, and others derived by cyclisation of δ,δ-bis(alkenyl) ketoximes or by iodine induced addition of acetaldoxime to cyclohexene, furnish isoxazolidines.

Solid phase sequential 1,3-dipolar cycloaddition–Pictet–Spengler reactions

Abstract Up to six bonds and two rings can be created, in five component processes (five points of diversity), by AgOAc catalysed imine cycloaddition to Wang resin acrylate followed by Pictet–Spengler and Pd(0) catalysed reactions.

PALLADIUM (II) CATALYSED TANDEM 2,3-SIGMATROPIC SHIFT 1,3-DIPOLAR CYCLOADDITION PROCESSES IN OXIME O-ALLYL ETHERS

Abstract Oxime O-allyl ethers are equilibrated with the corresponding N-allyl nitrones on treatment with 10 mol% PdCl 2 (MeCN) 2 by a formal [2,3]-sigmatropic shift. The nitrones can be trapped both inter- and intra-molecularly by appropriate dipolarophiles to give cycloadducts in good to excellent yields.

Effect of structure on tandem 1,2-prototropy-cycloaddition versus tandem cyclisation-cycloaddition reactions of oximes.

Abstract Aliphatic δ-alkenyl aldoximes in which the carbon centre a to the oxime moiety is tetrasubstituted undergo a tandem cyclisation-cycloaddition sequence via a 6-membered cyclic nitrone on heating in xylene. When the α-carbon centre is not tetrasubstituted the oximes react via a 1,2-protot ropy-cycloaddition sequence.

XY–ZH Systems as Potential 1,3-Dipoles. Part 50: Phenylselenyl Halide Induced Formation of Cyclic Nitrones from Alkenyl Oximes

Abstract Oximes possessing γ-, δ or ω-alkenyl substituents are cyclised by phenylselenyl bromide, or by phenylselenyl chloride and an appropriate silver salt to the corresponding cyclic nitrones; the seleno nitrones undergo facially specific cycloaddition reactions with N-methylmaleimide; bis(alk-γ,δ-enyl) ketones undergo regiospecific cyclisation and stereospecific intramolecular cycloaddition to furnish spirocyclic products.

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 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.