Studies on the Reaction of π-Deficient Heterocycles with Aromatic Aldehyde in the Presence of Cyanide Ion

Dimerization of π-deficient heterocyles by the catalytic action of cyanide ion in DMSO was carried out. Thus, reaction of quinoxaline (V), 1-phenyl-1H-pyrazolo [3, 4-d] pyrimidine (VI), 1-methyl-1H-pyrazolo [3, 4-d] pyrimidine (VII), and pyrido [2, 3-b] pyrazine (VIII) with cyanide ion gave 2, 2'-biquinoxaline (IX), 4.4'-bis [1-phenyl-1H-pyrazolo [3, 4-d] pyrimidine] (X), 4, 4'-bis [1-methyl-1H-pyrazolo [3, 4-d] pyrimidine] (XI), and 2, 2'-bipyrido [2, 3-b] pyrazine (XII), respectively, although the yields of these dimers were very poor. The formation of dimer is assumed to be oxidation following a benzoin condensation-like reaction by the catalysis of cyanide ion. Also we carried out the reaction of π-deficient heterocycles with aromatic aldehyde (XVI) in the presence of cyanide ion in DMSO, and found that the expected cross benzoin condensation-like reaction has developed. Thus, 4-isoquinolinecarbonitrile (II) reacted with XVI to give α-aryl-4-cyano-1-isoquinolinemethanol (XIX) and aryl 4-cyano-1-isoquinolyl ketone (XX) together with 1, 1'-biisoquinoline-4, 4'-dicarbonitrile (IV). Similarly, V and XVI gave α-aryl-2-quinoxalinemethanol (XXI) and aryl 2-quinoxalinyl ketone (XXII), VI and XVI afforded α-aryl-1-phenyl-1H-pyrazolo [3, 4-d] pyrimidine-4-methanol (XXX) and aryl 1-phenyl-1H-pyrazolo [3, 4-d] pyrimidin-4-yl ketone (XXXI), VII and XVI produced α-aryl-1-methyl-1H-pyrazolo [3, 4-d] pyrimidine-4-methanol (XXXIV) and aryl 1-methyl-1H-pyrazolo [3, 4-d] pyrimidin-4-yl ketone (XXXV), and VIII and XVI formed aryl 2-pyrido [2, 3-b] pyrazinyl ketone (XXXIV). It seems that XIX, XXI, XXX, and XXXIV are a formal product of a cross benzoin condensation-like reaction, and XX, XXII, XXXI, XXXV, and XXXVI are oxidation product of a formal product of the reaction. And limitation of this reaction was also discussed.