Allylic sulfides chlorination

The trichloro-l,2,3-triazine, trichloroisocyanuric acid (785), operates as a useful chlorinating agent (cyclohexene—> 3-chlorocyclohexene and naphthalene— 1-chloronaph-thalene) (70JOC719). It appears to be more effective than NCS in the conversion of phenyl allyl sulfides to the corresponding l-thiophenoxy-3-chloroalkenes (786 Scheme 182) (75TL4433). 

Trichloroisocyanuric acid, 2, 426-427 3, 297 5, 687. Trade name Chloreal. Chlorination of phenyl ally I sulfides. Cohen et al. have reported that this inexpensive reagent is more effective than NCS for chlorination of phenyl allyl sulfides to give l-thiophenoxy-3-chloroalkenes (equation I). 

Treatment of allyl sulfide 111 with dichloroketene, generated in situ by reductive elimination of chlorine from trichloroacetyl chloride, results in an intramolecular ketene Claisen rearrangement giving 779 with high, 2-syn selectivity (94% de). Reductive dechlorination and subsequent lactonization affords chiral butyrolactone 780, with an optical purity that exceeds 95%. 

Investigation of the kinetics of the reaction of 4-chloro-2-pentene, an allylic chloride model for the unstable moiety of polyfvinyl chloride), with several thermal stabilizers for the polymer has led to a better understanding of the stabilization mechanism. One general feature of the mechanism is complexing of the labile chlorine atom by the metal atom of the stabilizer. A second general feature is substitution of the complexed chlorine atom by a ligand (either carboxylate or mercaptide) bound to the metal. Stabilization requires that the new allylic substituent (ester or sulfide) be more thermally stable than the allylic chlorine. The isolation of products from stabilizer-model compound reactions supports the substitution hypothesis of poly(vinyl chloride) stabilization. 

Unlike other stabilizers, tin mercaptide, or the mercaptan that is formed after the HQ reacts with the mercaptide, can react with the allylic chlorine to produce a sulfide (47), thus eliminating the labile chlorine groups and stopping the unzipping. 

---