Cycloaddition reactions of nitrile oxides to silyl- and germyl-substituted thiophene-1,1-dioxides

Silyl- and-germyl substituted thiophene-1,1-dioxides were prepared from the corresponding thiophenes by oxidation with m-CPBA in CH2Cl2 at room temperature. The [2+3] dipolar cycloaddition of nitrile oxides to the double C=C bonds of thiophene-l,l-dioxides has been investigated. It was shown that the reaction pathway strongly depends on the substituents M and M' in the heterocycle and the method of nitrile oxide generation. The molecular structures of 2-tert-butyl-5-trimethylsilylthiophene-1,1-dioxide, 2-trimethylsilyl-5-trimethylgermylthiophene-1,1-dioxide, 2,5-bis(trimethylgermyl)thiophene-1,1-dioxide, and the mixture of 4,4-dioxo-3-phenyl-5-tert-butyl-3a,6a-dihydrothieno[2,3-d]isoxazoline-2 with 4,4-dioxo-3-phenyl-5-trimethylgermyl-3a,6a-dihydrothieno[2,3-d]isoxazoline-2 (92:8) were studied by X-ray diffraction.