Synthesis and [3+2] cycloaddition reaction of 3-[(trimethylsilylmethylamino)(methylthio)methylene]heterocyclic compounds

3-[(Trimethylsilylmethylamino)(methylthio)]methylene-2-coumaranone (4a) and 1-methyloxindole (4b), readily prepared by reactions of the corresponding bis(methylthio)methylene heterocyclic compounds (2a,b), with (trimethylsily lmethyl)amine (3), were found to be synthetic equivalents of heterocyclic a lkylidene-azomethine ylides. Reactions of 4a, b with reactive heterodipolar ophiles such as aldehydes and ketones and reactive alkenes in the presence of cesium fluoride gave the 1,3-dipolar cycloadducts, 3-(2-oxazolidinyliden e)-oxindole and -coumaran-2-one derivatives (8a-j, 9a-b), as well as pyrrol ylidenecoumaran-2-one and oxindole derivatives (12-15, 17, 18), via the 1,3 -elimination of (methylthio)trimethylsilane.