NOVELTY - Synthesis of 1,3,6-triimethyl-(1H,3H)-pyrimidine-2,4-dione comprises: Chapman rearrangement of 0.01 M 2,4-dimemoxy-6-methyl pyrimidine in a flask equipped with a water condenser by irradiating at 900 W in a micro wave reactor for 20 minutes; cooling the reaction mass to room temperature and treating with 50 ml ligroin; and filtering and recrystallizing to obtain 1,3,6-triimethyl-(1H,3H)-pyrimidine-2,4-dione.    USE - The method is useful for preparing 1,3,6-triimethyl-(1H,3H)-pyrimidine-2,4-dione, which is useful as pesticide, anti-photosynthetic herbicide, or insecticides. No biological data given.    ADVANTAGE - The method: is simple; is carried out under microwave irradiation thus it is green and environmental friendly (all claimed); and provides 1,3,6-triimethyl-(1H,3H)-pyrimidine-2,4-dione in less time, in less number of steps, and with improved yield.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) synthesizing 1,3-diethyl-(1H,3H)-6-methyl pyrimidine-2,4-dione comprising Chapman rearrangement of 0.01 M 2,4-diethoxy-6-methyl pyrimidine in a flask equipped with a water condenser by irradiating at 900 W in a micro wave reactor for 23 minutes, cooling the reaction mass to room temperature and treating with 50 ml ligroin, and filtering and recrystallizing to obtain 1,3-diethyl-(1H,3H)-6-methyl pyrimidine-2,4-dione;    (2) synthesizing 1,3-di-(2-butyl)-(1H,3H)-6-methyl pyrimidine-2,4-dione comprising Chapman rearrangement of 0.01 M 2,4-di-(2-butoxy)-6-methyl pyrimidine in a flask equipped with a water condenser by irradiating at 900 W in a micro wave reactor for 20 minutes, cooling the reaction mass to room temperature and treating with 50 ml ligroin, and filtering and recrystallizing to obtain 1,3-di-(2-butyl)-(1H,3H)-6-methyl pyrimidine-2,4-dione;    (3) synthesizing 1,3-di-(2-propyl)-(1H,3H)-6-methyl pyrimidine-2,4-dione comprising Chapman rearrangement of 0.01 M 2,4-di-(2-propoxy)-6-methyl pyrimidine in a flask equipped with a water condenser by irradiating at 900 W in a micro wave reactor for 20 minutes, cooling the reaction mass to room temperature and treating with 50 ml ligroin, and filtering and recrystallizing to obtain 1,3-di-(2-propyl)-(1H,3H)-6-methyl pyrimidine-2,4-dione;    (4) synthesizing 1,3-di-(1-propyl)-(1H,3H)-6-methyl pyrimidine-2,4-dione comprising Chapman rearrangement of 0.01 M 2,4-di-(1-propoxy)-6-methyl pyrimidine in a flask equipped with a water condenser by irradiating at 900 W in a micro wave reactor for 17 minutes, cooling the reaction mass to room temperature and treating with 50 ml ligroin, and filtering and recrystallizing to obtain 1,3-di-(1-propyl)-(1H,3H)-6-methyl pyrimidine-2,4-dione;    (5) synthesizing 1,3-di-(1-butyl)-(1H,3H)-6-methyl pyrimidine-2,4-dione comprising Chapman rearrangement of 0.01 M 22,4-di-(1-butoxy)-6-methyl pyrimidine in a flask equipped with a water condenser by irradiating at 900 W in a micro wave reactor for 17 minutes, cooling the reaction mass to room temperature and treating with 50 ml ligroin, and filtering and recrystallizing to obtain 1,3-di-(1-butyl)-(1H,3H)-6-methyl pyrimidine-2,4-dione; and    (6) 2,4-dialkoxy-6-methyl pyrimidines underwent facile Chapman rearrangement under microwave irradiation to afford 1,3-dialkyl-6-methyl pyrimidine-2,4-diones.