Triarylmethyl Cation‐Catalyzed Three‐Component Coupling for the Synthesis of Unsymmetrical Bisindolylmethanes

Abstract

An efficient synthesis of unsymmetrical bisindolylmethanes has been accomplished using triarylmethyl cations to catalyze the reaction of N‐arylimines with two different indoles. Optimization of the organocatalyst by tuning cation stability allows for excellent single addition selectivity when coupled with p‐nitrophenyl imines. The optimal catalyst is commercially available, and the reaction minimizes waste and environmental impact by employing a one‐to‐one ratio of starting materials. The intermediates can be isolated or used in situ in a one‐pot two‐step reaction to generate unsymmetrical bisindolylmethanes in high yields. The reaction tolerates a broad range of imines with the highest yields observed for electron‐poor and neutral imines. A wide range of indole nucleophiles are also successfully employed allowing for the creation of a large variety of unsymmetrical bisindolylmethanes.

Synthesis of Bis(3‐indolyl)methanes Mediated by Potassium tert‐Butoxide

“… [14] Other examples also include the use of metal‐free oxidative reactions. [ 15 , 16 ] Recently, several examples have been reported using aryl amines ( 1 ), [17] aldehydes ( 2 ),[ 18 , 19 , 20 , 21 , 22 ] ketones ( 3 ),[ 23 , 24 ] benzyl amines ( 4 )[ 16 , 25 ] and benzyl alcohols ( 5 )[ 26 , 27 , 28 ] as starting materials (Scheme 1 ).…”

Donor‐Acceptor Tin(IV) Complexes with α‐Diimine and Catecholate Ligands

“…[23] Tin amalgam was prepared by dissolving tin metal in liquid mercury. [24] 3,6-di-tertbutyl-o-quinone, [25] 2,6-dimethyl-N-(2-pyridylmethylene)aniline, [26] N-(2-pyridylmethylene)benzene-1,4-diamine, [27] 4-nitro-N-(2pyridylmethylene)benzenamine, [28] N-(4-[2-phenyldiazenyl]phenyl)-N-(2-pyridinylmethylidene)amine [29] and 1,4-di-isopropyldiazadiene-1,3, 1,4-di-tert-butyldiazadiene-1,3, 1,4di-cyclohexyldiazadiene-1,3, 1,4-di-adamantyl-diazadiene-1,3 [30] were synthesized according to literature procedures. The synthesis of bis(3,6-di-tert-butylcatecholato)tin(IV) etherate (Cat 2 Sn(Et 2 O) 2 ) was performed by reduction of 3,6-di-tert-butyl-o-quinone with an excess of tin amalgam in diethyl ether according to the previously published procedure.…”