Synthesis of Phenanthrenol Derivatives Through Polar Diels-Alder Reactions Employing Nitronaphthalenes and (E)-1-(Trimethylsilyloxy)-1,3- butadiene. Theoretical Calculations
María N. Kneeteman, Claudia D. Della Rosa, Carla M. Ormachea, Paula Giménez, Anna F. Lopez Baena and Pedro M.E. Mancini
Affiliation: Facultad de Ingeniería Química, Universidad Nacional del Litoral, Santiago del Estero 2829, 3000 Santa Fe, Argentina.
Keywords: Phenanthrenols, Diels-Alder reaction, nitronaphthalenes, electrophiles, theoretical calculations.
The cycloaddition reactions between dinitronaphthalenes and (E)-1-trimethylsilyloxy-1,3-butadiene produce
nitrophenanthrenol derivatives as principal products. The primary adducts suffer the irreversible lost of nitrous acid and,
consequently, the aromatization. In these reactions it is frequent to observe the presence of naphthalenyl-1H-pyrrole
derivatives as a result of a hetero Diels-Alder process, which is competitive with the normal way. The global electrophilic
character of the dienophile is responsible of these results. Other dienes (or dienophiles/electrophiles) with electron donor
substitution in C-1 show a different behavior in which the hetero Diels-Alder products prevail. In the series explored only
the substrate 1-cyano-4-nitronaphthalene produces the naphthalenyl-1H-pyrrole derivative as principal product, probably
as a consequence of its charge distribution. A combination between stereoelectronic effects in the electrophile and the type
of substitution joint to the nucleophilicity of the diene is responsible of the results and regioselectivity observed in these
polar cycloaddition reactions. In all the cases studied the regioselectivity expected by theoretical calculations corresponds
with the ones obtained experimentally.
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