Sulfenylation rearrangement mechanism

The sulfenylation-rearrangement mechanism for compound 6 would require the formation of intermediate 11 (Scheme 2.8). However, fire C=N bond in 6 is less electrophilic than the iminium bond of the intermediate 9 in Scheme 2.7 and hence, the nucleophilic attack by the adjacent SPh group should be less favored. In addition, even if 11 is formed, flie rearrangement to 7 by ring opening and protonation of the nitrogen, does not require (in principle) any extra amount of the reagent. 

Scheme 2 summarizes the mechanism for the formation of thiosulfonate from sulfinyl radicals it is shown that the sulfinyl radicals combine to give both yic-disulfoxides and O, S-sulfenyl sulfinates, although they may rearrange to thiosulfonates either via a free radical route or via a concerted mechanism. The reader is referred to the recent review of Freeman22, who has collected and discussed the vast amount of information published on yic-disulfoxides and O, S-sulfenyl sulfinates. 

The mechanism written in Scheme 2.7 would explain the mixtures of products obtained in the sulfenylation of 3-(phenylthio)indole 3 wifli methanesulfenyl chloride (Scheme 2.3). However, would it explain fire transformation of 3,3-bis-phenylthio derivative 6 into 2,3-bis-phenylthioindole 7 depicted in Scheme 2.4 We should remember that in fliis case a full equivalent of sulfenyl chloride is required for the completion of flie reaction. Considering fliis fact, if compound 7 were formed just by rearrangement of 6 no extra sulfenyl chloride would be needed. What for compound 6 requires the extra equivalent of reagent ... 

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