Thermal racemization and cis,trans-isomerization of allylically unsaturated di- and poly-sulphides: a mechanism involving branched sulphur chains

[2, 3] Sigmatropic Rearrangements on Lithiation of Some Allyl Sulfides. Preliminary communication

“…[l] R Full paper to appear in Helv sulfide (or analogue with different substituents), [2,3] sigmatropic change2) with formation of a metal thiolate might occur. This new reanangement would be analogous to that of the corresponding ylids, and more directly, to the Wittig rearrangement of ally1 ethers [7] [8] [9].…”

“…1 and 2 are lithiated in the benzyl position. The lithium compounds so formed rearrange rapidly by [2,3] sigmatropic change2). The reaction with butyllithium is the rate-determining step.…”

“…and 8 (R = H or CH,), respectively, in almost quantitative yields. Again, only the products of [2,3] sigmatropic change are detected.…”

Dechalcogenative Allylic Selenosulfide and Disulfide Rearrangements: Complementary Methods for the Formation of Allylic Sulfides in the Absence of Electrophiles. Scope, Limitations, and Application to the Functionalization of Unprotected Peptides in Aqueous Media.

“…52 More tangentially related are the reported use of morpholine or piperidine to drive the related allylic sulfoxide/sulfenate rearrangement, 60 and the uptake of molecular sulfur by allylic sulfides leading to rearranged allylic disulfides. 56 The apparent acid-catalyzed rearrangement of 103 to 85 with loss of sulfur could not be developed into a satisfactory general method. However, after some investigation, we have found that the rearrangement can be achieved by stirring with two equivalents of piperidine at room temperature in methanol, or simply by heating to reflux in methanol with no added thiophile for a period of several hours.…”

“…The phosphine-promoted desulfurative allylic rearrangement of diallyl disulfides to give allyl sulfides [53][54][55][56][57] proceeds by way of a [2,3]-sigmatropic rearrangement via a diallyl thiosulfoxide intermediate 58,59 and, thus, is closely related to the well known Evans-Mislow rearrangement of allylic sulfoxides. 60 This dechalcogenative rearrangement, which may also be induced to operate in the reverse direction on treatment of allyl sulfides with elemental sulfur, 61 and which is potentially important in the chemistry of essential oils derived from garlic, 62 appeared to us to hold promise as a means of rendering disulfides permanent if it could be caused to function at ambient temperatures in protic solvents.…”