Seleno-Pummerer rearrangement

Seleno-Pummerer rearrangement. Diacetonylselenium dichlorides (1) when treated with triethylamine rearrange to a-chloro selenides (2).1... 

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. 

Dithiole-2-one (60), which can be readily transformed into its thio- or seleno-carbonyl derivatives, is a key intermediate for the synthesis of tetrathiafulvalene (Scheme 13)[31]. We first anticipated that compound 57, a Michael addition product of xanthate 54 to vinyl sulfoxide, might be an ideal intermediate for the synthesis of 60 via cyclization under Pummerer rearrangement conditions. However, although Michael addition of dithiocarbamate 53 to vinyl sulfoxide proceeded smoothly to yield compound 55, the addition reaction with xanthate 54 failed. We then turned to the alkylation approach. Xanthate 54 was alkylated smoothly with 56, which served as the synthetic equivalent of the vinyl sulfoxide, in ethanol under sonication in 90% yield [32]. Cyclization of 57 under Pummerer rearrangement conditions in the presence of trifluoroacetic acid afforded 58 in 79% yield. Sodium metaperiodate oxidation gave the unstable sulfoxide 59 which underwent thermal elimination to yield 60 in refluxing benzene in moderate yield. 

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