2-[(Trimethylsilylmethylamino)(methylthio)]methylene-1,3-indandione (1), readily prepared by reaction of the corresponding 2-bis(methylthio)-methylene-1,3-indandione (7) with trimethylsilylmethylamine (8), was found to be a synthetic equivalent of carbonyl alkylidene-azomethine ylide. Reaction of 1 with reactive hetero-dipolarophiles such as aldehydes and ketones and reactive alkenes in the presence of cesium fluoride gave 1,3-dipolar cycloadducts, 2-(1,3-dioxoindan-2-ylidene)-1,3-oxazolidines (5a-i) and 2-(1,3-dioxoindan-2-ylidene)pyrrolidines (6a-c).