RESUMO
The deprotonation and regioselective reaction of 2H-pyrazolo[3,4-c]quinolines with a variety of electrophiles is described. Electrophiles include benzaldehyde, DMF, carbon dioxide, and iodine. This method provides a direct route to a class of pharmacologically interesting compounds.
Assuntos
Pirazóis/síntese química , Quinolinas/síntese química , Benzaldeídos/química , Dióxido de Carbono/química , Dimetilformamida/química , Iodo/química , Pirazóis/química , Quinolinas/químicaRESUMO
A new method is described for the intramolecular pinacol coupling of 1,5- and 1,6-dicarbonyl compounds, employing Bu(3)SnH as the stoichiometric reductant. The key steps in this pinacol cyclization are the addition of a tin ketyl to a carbonyl group and a subsequent intramolecular S(H)2 reaction. The isolation of 1,3-dioxa-2-stannolanes, along with other product and labeling studies, provides strong support for the proposed homolytic substitution step, which distinguishes the pinacol cyclization from other reductive cyclizations of tin ketyls, all of which proceed through abstraction of hydrogen from Bu(3)SnH in the final step. An interesting consequence of the S(H)2 pathway is very high cis selectivity in the cyclization of 1,5-dicarbonyl compounds. Mechanistic studies furnish evidence that the steps that precede homolytic substitution, including C-C bond formation, are reversible under the reaction conditions.
