Azomethines with electron withdrawing substituents II. 1,4-Cycloaddition of sulfonyl or acyl isonitrosomalono compounds with cyclopentadiene

Intramolecular [4 + 2] cycloadditions of iminoacetonitriles: a new class of azadienophiles for hetero Diels-Alder reactions

Iminoacetonitriles participate as reactive dienophiles in stereoselective intramolecular hetero Diels-Alder reactions which afford substituted quinolizidines. The cycloadduct with exo-oriented cyano group is obtained as the major or exclusive product of the reaction as a consequence of the alpha-amino nitrile anomeric effect The alpha-amino nitrile moieties incorporated in the cycloadducts constitute latent iminium ions, which upon exposure to mild protic or Lewis acids are unmasked, setting the stage for further useful synthetic transformations. For example, reductive decyanation with NaBH3CN excises the cyano group, while Bruylants reaction with Grignard reagents and acetylides lead to alpha-substituted amines. The substrates for these [4 + 2] cycloadditions are prepared from readily available alcohols via a Mitsunobu coupling reaction with the previously unknown, easily prepared reagent HN(Tf)CH2CN followed by cesium carbonate promoted elimination of trifluoromethanesulfinate.

Methodology for regioselective synthesis of substituted pyridines via intramolecular oximino malonate hetero Diels-Alder reactions

[structure] Various substituted pyridines can be prepared regioselectively by a sequence involving an intramolecular thermal or high-pressure Diels-Alder cycloaddition of an oximino malonate dienophile tethered to a dienic carboxylic acid, followed by mild aromatization of the resulting cycloadduct with cesium carbonate in DMF at room temperature.