Coupling of Diazopurines, a Curious Steric Effect in a Free Radical Reaction

Article abstract of DOI:10.1021/jo00146a013

The reaction of adenine derivatives with nitrite esters in the presence of arenes was examined and found to give 6-arylpurines in good (83percent) to poor (11percent) yield.The arylated products consisted only of the meta and para isomers; none of the anticipated ortho isomers were found.The predominance of meta- and para-substituted products is attributed to steric effects.The evidence that the reaction proceeds via a purine radical includes light stimulation, relative insensitivity to electronic factors, and the facile reaction of the purine intermediate with pyridine N-oxide.Photolysis of 6-iodo-9-benzylpurine in the presence of anisole gave the same mixture of 6-(m-methoxyphenyl)- and 6-(p-methoxyphenyl)purine as did diazotization, suggesting that both reactions involve the same purine radical.