Enhanced Efficiency of Thiourea Catalysts by External Brønsted Acids in the Friedel-Crafts Alkylation of Indoles
Eugenia Marqués-López, Ana Alcaine, Tomás Tejero, Raquel P. Herrera. Enhanced Efficiency of Thiourea Catalysts by External Brønsted Acids in the Friedel-Crafts Alkylation of Indoles . . 2011, Vol. 2011, p. 3700-2011.
A novel study of external Brønsted acid-assisted thiourea catalysts in the asymmetric Friedel-Crafts alkylation of indoles with nitroalkenes is reported. The final 3-substituted indoles derivatives are synthesized with better results by cooperative effect between chiral thiourea and a Brønsted acid additive (1a•HA), than those obtained with sole thiourea catalyst 1a. The effect of diverse catalysts, different acid additives, solvent and temperature of the reaction are also explored. The high reactivity and selectivity of the reaction is presumptively attributed to an appropriate assembly between the Brønsted acid and the thiourea structure, affording catalytic complex more acid and rigid.
A novel study of external Brønsted acid-assisted thiourea catalysts in the asymmetric Friedel-Crafts alkylation of indoles with nitroalkenes is reported. The final 3-substituted indoles derivatives are synthesized with better results by cooperative effect between chiral thiourea and a Brønsted acid additive (1a•HA), than those obtained with sole thiourea catalyst 1a. The effect of diverse catalysts, different acid additives, solvent and temperature of the reaction are also explored. The high reactivity and selectivity of the reaction is presumptively attributed to an appropriate assembly between the Brønsted acid and the thiourea structure, affording catalytic complex more acid and rigid.