X=Y-ZH systems as potential 1,3-dipoles. Part 33. Generation of nitrones from oximes. Tandem Michael addition-1,3-dipolar cycloaddition reactions. Class 2 processes in which the dipolarophile is located within the oxime.
corresponding C-alkenyl nitrones which undergo an intramolecular cycloaddition. The cycloaddition can occur by one of two modes leading to either bridged- or fused-isoxazolidines. The latter is preferred in most cases except that of the C-(3-alkenyl) nitrone which gives exclusively the bridged-ring product and the C-(4-alkenyl)nitrones derived from N-allylpyrrole-2-carboxyaldehyde oxime which gives both bridged-
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
作者:Jasothara Markandu、H. Ali Dondas、Martyn Frederickson、Ronald Grigg
DOI:10.1016/s0040-4020(97)00838-7
日期:1997.9
Regiospecific nucleophilic substitutionreactions involving attack of the nitrogen atom of oximes on epoxides are used to generatenitrones which are then trapped in 1,3-dipolar cycloadditionreactions. These tandem processes are shown to be flexible and to have wide synthetic scope for the construction of complex molecular frameworks.
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 cyclicnitrones; 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
Substituent effects on intramolecular dipolar cycloadditions: The gem-dicarboalkoxy effect
作者:Michael E Jung、Binh T Vu
DOI:10.1016/0040-4039(95)02196-5
日期:1996.1
A gem-dicarboalkoxy effect (rel. rate >20) has been measured and good diastereoselectivity (∼9:1) has been seen for the intramolecular dipolar cycloaddition of 3-substituted 5-hexenyl nitrile oxides.
δ,ϵ-Unsaturated oximes, on heating with O-alkyl S-(pyridin-2-yl)carbonothioates (PySCO2R) in refluxing toluene, undergo intramolecular cycloaddition to give N-alkoxycarbonylated multi-cyclic compounds. Mechanistic studies indicate that the reaction involves direct generation of N-alkoxycarbonyl nitrones followed by cycloaddition, instead of intramolecular oxime-olefin cycloaddition (IOOC) followed