Several N, N-diethyl-2-acylmethylbenzamides (6) were prepared from N, N-diethyl-2-toluamides (4), and the ketoamides (6) were easily cyclized to the corresponding 3-substituted isocoumarins (8) by heating in acetic acid or xylene. This simple procedure was applied to the synthesis of thunberginol A (1), thunberginol B (2), thunberginol F (14), and a key-intermediate (8j) for achlisocoumarin I (3).