Reaction with oxazine iminium salts

The reaction has been extended to the preparation of ketones 1542 treatment of a dihydro-1, 3-oxazine (133) with methyl iodide forms the iminium salt 134 (0-43) which, when treated with a Grignard reagent or organolithium compound (6-35), produces 135 which can be... 

A completely new cyclization reaction is the PhSeBr promoted conversion of alkenyl nitrones into 1,2-oxazines, which was recently reported by Tiecco [79]. This are the first examples to use alkenyl nitrones to effect ring closure reactions induced by electrophilic reagents. As indicated in Scheme 20, the nitrones 130 and 134 react with PhSeBr to give the cyclic iminium salts 131 and 135, respectively. These intermediates suffer attack by nucleophilic reagents at the partially positive carbon atom. The nature of the final products depends on the structure of the starting nitrone and of the nucleophile employed. Thus, the intermediate... 

A cycloaddition reaction of the halogen-substituted nitrone (289) with olefins in the presence of AgBp4 provides reactive iminium salts in a regio- and stereo-specific manner. These react with various nucleophiles to give 1,2-oxazine derivatives as shown. In a study of the reactions of P-enamino-esters with carbonyl compounds, WamholF et have isolated a series of acyclic and... 

The iminium ion electrophile can also be prepared separately, as a crystalline solid known as Eschen-moser s salt (Me2N =CH21 ) and, with this, the reaction is normally carried ont in a non-polar solvent. Examples that illnstrate the variation in iminium ion structure that can be tolerated include the reaction of indole with quinolines, catalysed by indium(lll) chloride, with benzylidene derivatives of arylamines, catalysed by lanthanide triflates, with ethyl glyoxylate imines " (no catalyst required) and with dihydro-1,4-oxazin-2-ones. °" ... 

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