On the inapplicability of the Lehnert reagent for 1,2-dicyanomethylation of 2,5- and 2,6-diphenylthiobenzoquinones: synthesis and structure of isomeric 2-amino-5-hydroxy-4,6- and 2-amino-5-hydroxy-4,7-diphenylthiobenzo[b]furan-3-carbonitriles

Abstract

The Lehnert reagent (TiCl₄–pyridine) has been shown not to activate the carbonyl groups of dithiophenyl-substituted benzoquinone isomers in nucleophilic attack by dicyanomalonate. Instead, 1,4-addition to the quinone ring results in the title benzofuran derivatives. The reaction mechanism is shown to be unlike those where carbon atoms are attached to the quinone ring or when the sulphur atom is part of an aromatic system. The crystal data of 2-amino-5-hydroxy-4,6-diphenylthio-benzo[b]furan-3-carbonitrile are: triclinic, P1, a= 10.092(6), b= 10.828(7), c= 9.976(6)Å, α= 73.35(5), β= 100.13(4), γ= 116.13(4)°, V= 936.2(9)ų, Z= 2. The proposed reaction mechanism and the crystal structure of the title compound are presented and discussed.