OXIDATION OF 3,4-DI-TERT-BUTYLTHIOPHENE 1,1-DIOXIDE

The oxidation of 3,4-di-tert-butylthiophene 1,1-dioxide (4) by a variety of reagents under various conditions was investigated in detail. Oxidation of 4 with peracids (MCPBA, trifluoroperacetic acid) affords the thiete 1,1-dioxide 6 and the sulfone 7, both in moderate yield. The formation of these compounds can be explained as being the result of an acid-catalyzed rearrangement of the initial product, epoxy sulfone 5 via the carbocation 8. Under basic conditions the rearrangement is suppressed and thus 5 can be isolated in good yield. Treatment of 5 with BF3.Et2O affords 6 and the sultine 10. Oxidation of 4 with alkaline H2O2 involves a smooth Michael addition of HOO- to give the hydroperoxide 17 in high yield. This represents the first example of the formation of an isolable beta-hydroperoxy sulfone, a species which has been hypothesized to be an intermediate in the formation of epoxy sulfones by the oxidation of alpha,beta-unsaturated sulfones with alkaline H2O2. Thermal decomposition of 17 affords the ketone 19 quantitatively. Reduction of 17 with NaBH4 gives the alcohol 20. On treatment with base, both 17 and 20 undergo ring opening to yield the alkene 18 in good yield.