The reactions of 2,2-dimethyl-l,3-indandione (I) with several Wittig reagents have been studied. When I was reacted with one or two equimolar amounts of active phosphoranes, such as methylene and ethylidenetriphenylphosphorane, bismethylene- and bisethylidene deriva- tives of the indandione were obtained in fairly good yields. The reactions of I with resonance- stabilized phosphoranes such as ethoxycarbony!methylene-2—butylidene— and carboethoxy— 2-methyl-2-propylidenetriphenylphosphorane gave monoalkylideneindanones in moderate or in pocr yields at severe conditions. On the contrary, the reaction of I with carboethoxymethyle- netriphenylphosphorane in sealed tube gave the bisalkylidene derivative of the indandione at 160°C.