Synthesis of alkyl allenyl sulfoxides from thiosuccinimides via [2,3]-sigmatropic rearrangement

With the instability and alternative reactive modes of alkyl sulfenyl chlorides making the synthesis of a broad range of alkyl allenyl sulfoxides via the [2,3]-sigmatropic rearrangement difficult, alternative sources of electrophilic sulfur were explored. Examination of various N-sulfanylimides revealed that thiosuccinimides are a viable sulfur source for the synthesis of alkyl allenyl sulfoxides via the [2,3]-sigmatropic rearrangement. With the optimized conditions of excess propargyl alcohol and potassium carbonate in chloroform at 50 degrees C, a variety of alkyl allenyl sulfoxides were synthesized in fair to good yields (21-73%, 21 examples). Additionally, butyn-1,4-diols can be selectively monofunctionalized with a large excess of diol and stoichiometric triethylamine in THF at room temperature to form 1-hydroxyalkyl allenyl sulfoxides (26-71%). These diols can also be bis-functionalized to form 2,3-disubstitued dienes (53-66%) via two separate [2,3]-sigmatropic rearrangements. The formation of alkyl allenyl sulfoxides was also found to be selective for less substitution at the propargyl position (3:1-100:0 ratio) as shown in direct competition experiments. Trimethylsilylethyl thiosuccinimides were among the highest yielding of the thioimides. The sulfenate chemistry of select allenyl sulfoxides can be successfully performed.