Conceptual density functional theory (chemical hardness η, electronic chemical potential µ, global and local electrophilicity index ω and ω k , Fukui function f + k) is used to predict reactivity, stereo-and regioselectivity of the Diels-Alder (DA) reaction between 2-nitropyrrole and its 1tosylated derivative with Danishefsky's diene to yield 5-hydroxyindoles. A detailed mechanistic study of various possible reaction channels is done by DFT [B3LYP/6-31G(d)] calculations. Solvent effects (benzene) are taken into account by the CPCM bulk solvation model. In principle, the nitropyrrole can either act as diene involving the nitro group (hetero Diels-Alder reaction, HAD) or alternatively as alkene in a "normal" Diels-Alder reaction. The experimentally observed product 5-hydroxy-1-tosylindole can be formed either directly by Diels-Alder reaction of the nitropyrrole acting as alkene or by rearrangement of the dihydrooxazine N-oxides. The primary cycloadduct with the nitropyrrole acting as alkene is found to be unstable reacting further by extrusion of nitrous acid to 5-hydroxyindole. Finally, the results are compared with those obtained for the analogous furans, thiophenes, and selenophenes.
In this work the polar Diels-Alder reactions between 2-and 3-nitrobenzothiophenes derivatives and different dienes such as 2-methyl-1,3-butadiene and 1-trimethylsilyloxy-1,3butadiene are studied. Molecular solvent and protic ionic liquids are employed as reaction media. The presence of a very strong electron-acceptor group such as nitro, improve the electrophilic character of these heterocyclic compounds. Moreover, this substituent is easily extruded under thermal conditions make this reaction sequence a simple method of organic compound families with heteroatom rings preparation.
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