AbstractSome organolithium‐diazine adducts and some dihydropyrimidines were treated with electrophilic reagents. Both 4,6‐diphenyl‐1(3)‐lithio‐1,4(3,4)‐dihydropyrimidine and 4,6‐diphenyl‐1,4(3,4)‐dihydropyrimidine were attacked by the electrophilic reagent methyl iodide (methyl chloroformate) at N(3), yielding 4,6‐diphenyl‐3‐methyl(methoxycarbonyl)‐3,4‐dihydropyrimidine. 4,4,6‐Triphenyl‐1,4(3,4)‐dihydropyrimidine upon treatment with methyl iodide gave mainly 3‐methyl‐4,4,6‐triphenyl‐3,4‐dihydropyrimidine. The 3,4‐dihydro structure. of the products was established both spectroscopically and chemically. Reaction of 2‐lithio‐3‐methyl‐2,3‐dihydropyridazine with methyl iodide (methyl chloroformate, tosyl chloride) gave the corresponding 2,3‐dimethyl(2‐methoxycarbonyl‐3‐methyl‐, 2‐tosyl‐3‐methyl)‐2,3‐dihydropyridazine. Reaction of 1‐lithio‐4‐methyl‐ 1,4‐dihydropyridazine with methyl iodide (methyl chloroformate) gave 1,4‐dimethyl(l‐methoxycarbonyl‐4‐methyl)‐1,4‐dihydropyridazine. 1‐Lithio‐2‐phenyl‐1,2‐dihydropyrazine upon treatment with methyl iodide afford