Selenoxide, Pummerer rearrangement

Pummerer rearrangement. y-Sulfinyl acids give y-thio-y-butyrolactones. In a lenium version, the rearrangement product (with a a,a-difluorinated selenoxide). an react with cyclic ethers. 

In another example, addition of phenyl vinyl selenoxide into a mixture of an indanedione, hexamethyldisilazane, and TMSCl in dichloromethane affords the a-trimethylsiloxyselenide in 70% yield (eq 67). The reaction proceeds through a sequence of in situ formation of TMS silyl enol ether, Michael addition onto the phenyl vinyl selenoxide, and seleno Pummerer rearrangement of the resulting selenoxide. Trifluoroacetic anhydride and various other trialkylchlorosilanes give the same product for this reaction, but in much lower yields. 

Reactions of Saturated Sulphoxides and Selenoxides.—The main reactions of saturated sulphoxides and selenoxides are associated with the nucleophilic properties of the sulphinyl and seleninyl groups, and their activating effect on the adjacent saturated carbon atoms. The Pummerer rearrangement (as well as rearrangements of unsaturated sulphoxides discussed in a later section) and alkene-forming eliminations are instances of the former property the main consequence of the latter property, the formation of sulphinyl-stabilized carbanions, is covered in Chapter 2. 

Pummerer reaction the reaction of a sulfoxide or selenoxide with an acidic or electrophilic reagent, with cleavage of the S-O or Se-0 bond and formation of an S- or Se-stabilized carbenium ion that rearranges or reacts further with nucleophiles... 

---