Thiophilic addition of organolithiums to trithiocarbonate oxides (sulfines) - Synthesis of beta-oxoketene dithioacetals, 1,4-dicarbonyl compounds, and allyl sulfoxides

Reaction of trithiocarbonates with meta-chloroperoxybenzoic acid in CH2Cl2 at 0 degrees C affords the corresponding S-oxides. These sulfines are relatively stable compounds which can be purified by chromatography. They react readily with organolithiums in THF at -78 degrees C in a thiophilic manner to give carbanions which are stabilized by three sulfur groups. Hydrolysis affords trithioorthoester oxides, The thermal behaviour of these hindered products has been investigated and new rearrangement processes have been evidenced. The former carbanions are soft nucleophiles:I,4-addition of these intermediates to alpha-enones was achieved selectively to lead to beta-oxo ketenedithioacerals, which are easily transformed into 4-oxoalkanethioates, This ''Umpolung'' route allows the formal use of the (alkylthio)carbonyl anion. A thiophilic addition was also observed with allylsilanes in the presence of n-Bu(4)NF furnishing allyl sulfoxides. (C) 1997, Elsevier Science Ltd.