Regioselective Arylation of 1,3-Dimethyllumazine and Its 5-Oxide by Diazonium Salts

Abstract

SummaryA new method to introduce an aryl group directly into the pteridine nucleus by the action of arene diazonium salt in an aqueous alkaline solutio n is described. 1,3-Dimethyllumazine and benzene diazonium chloride reacts in an aqueous solution at pH 8-9 to give 7 -phenyl-1 ,3-dimethyllumazine together with a little of 6-phenyi-1 ,3-dimethyllumazine . The analogous reactions of 1,3-dimethyllumazine with 4-methyl-, 4-methm.),-, 4-chloro-, and 3-chlorobenzene diazonium chlorides give the corresponding 7-aryl-1,3-dimethyllumazines as major products together with a little of 6-aryl-1,3-dimethyllumazines. Reactions of 1,3-dimethyllumazine 5-oxide with arene diazonium salts under the same conditions exclusively afford the corresponding 6-aryl-1,3-dimethyllumazine 5-oxides which are easily converted to 6-aryl-1,3-dimethyllumazine by the action of tributylphosphine. Mechanisms concerning regioselectivities are investigated by using molecular orbital calculations.