Employment of nitriles in the stereoselective cycloaddition to nitrones

Umpolung reactions at the α-carbon position of carbonyl compounds

“…Carbon nucleophiles that have been added to vinylnitroso compounds include electron-rich arenes and heteroarenes, 12 malonates, 13 1,3-diketones, α-keto esters, Grignard reagents, 13 acetylides, 13,14 and simple ketone enolates. 15 Thus, vinylnitroso compounds 22 can act as enaminylium ion equivalents.…”

1,3-dipolar cycloaddition of nitrones to free and coordinated nitriles: Routes to control the synthesis of 2,3-dihydro-1,2,4-oxadiazoles

“…The cycloaddi tion of dinitrile 26 to nitrones affords two sterically less hindered diastereomers 30 of four possible diaste reomers. 65 2.4. The solvent effect.…”

“…Compounds 27 and 28 containing the CO 2 H or H substituents in the geminal position with respect to the CN group are not involved in the 1,3 DCA reaction even upon prolonged heating of the reaction mixture under high pressure, and only ni triles 25 and 26 bearing the second CN group in the geminal position react with nitrones R´´´R″C=NO(R´) to give 2,3 dihydro 1,2,4 oxadiazoles 29 and 30. 65 For ylidene malononitriles 21 (see Scheme 4) acting as bifunctional dipolarophiles, it was found that mono substituted compounds (X 1 = H) are readily involved in the cycloaddition, which occurs selectively at the CN group, the reactions with nitriles containing groups X 2 with both strong electron releasing and pronounced electron with drawing properties proceeding more easily. The reactivity of nitrile 21 substantially depends on the nature of the β substituent X 2 .…”

Recent Advances in Microwave-Assisted Synthesis of Heterocyclic Compounds

“…Nevertheless, several cycloadditions of nitrones with nitriles have been reported [49][50][51][52]. Unfortunately, these reactions require forcing conditions such as high pressure or extended reaction times at elevated temperatures to achieve the desired cycloadducts in acceptable yields.…”