SYNTHESIS OF 1,2,4-TRIAZIN-5-ONES THROUGH [4+2] CYCLOADDITION OF 1,2,4-TRIAZA-1,3-DIENES WITH DIPHENYLKETENE

On heating 1,2,4-triaza-1,3-dienes 1 with diphenylketene, [4+2] cycloaddition took place smoothly to afford the corresponding 1,2,4-triazin-5-one derivatives 2 in good yield.