Cycloaddition reactions of nitrile oxides to 2,4-silyl- and germyl-substituted thiophene-1,1-dioxides

2,4-Silyl- and germyl-substituted thiophene-1, 1-dioxides as well as 5,5 '- and 4,4 ' -bis(trimethylsilyl)-2,2 ' -bithiophene-1,1-dioxides were prepar ed from the corresponding thiophenes and bithiophenes by oxidation with m-C PBA in CH2Cl2 at room temperature, The [2+3] dipolar cycloaddition of nitri le oxides to the double C=C bonds of thiophene-l,l-dioxides has been invest igated. It was shown that in the series of 2,4-disubstituted thiophene-1,1- dioxides only the C-(4)=C-(5) double bond interacts with acetonitrile oxide to give fused thienoisoxazolines. Addition of acetonitrile oxide to 5,5 ' -bis(trimethylsilyl)-2,2 ' -bithiophene- 1,1-dioxide was accompanied by des ilylation. Isomeric 4,4 ' -bisitrimethysilyl)-2,2 ' -bithiophene- l,l-dioxi de was inactive in the reaction with acetonitrile oxide. Cycloaddition of b enzonitrile oxide with all mentioned sulfones did not occur. The molecular structures of 2,4-bis(trimethylsilyl)thiophene-1,1-dioxide, 2-trimethylgerm yl-4-trimethylsilylthioph-1,1-dioxide, 2-trimethylsilyl-4-trimethylgermyl-1 ,1-dioxde, 2,4-bis(trimethylgermyl)thiophene-dioxide, 5,5 ' -bis(trimethyls ilyl)-2,2 ' -bithiophen-1,1-dioxide, and 4,4-dioxo-3-methyl-5,6a- bis(trime thylgermyl)-3a,6a-dihydrothieno [2,3-d]isoxazoline-2 were studied by X-ray diffraction.