Allylic substituents that will induce

Examples of substrate-induced 1,2 diastereoselection have been recorded for [2,3] rearrangements of allylic ethers 12 which possess an additional allylic oxygen substituentl0-15. The observed diastereofacial selectivity is consistent with theoretical models78 which predict that stercoelectronically favored conformations for intramolecular nucleophilic addition to olefin 12 will be those for which the allylic CO cr-bond is coplanar with the 7 -system of the olefin, maximizing n-transition state. Of the two conformers which satisfy this stereoelectronic requirement, the isopropyl outside orientation, which minimizes steric interactions of the allylic substituent, predominates and is reflected in the observed diastereoselection of the rearrangement15. 

Sulfur is available to the compounder in two forms amorphous and rhombic. The amorphous form, also known as insoluble sulfur is a metastable high polymer that is insoluble in rubber and most solvents. Rhombic sulfur, a ring of eight sulfur atoms, is soluble in rubber and the form normally used for vulcanization. About 1 to 3 phr (parts per 100 parts of rubber elastomer) of sulfur are used for most rubber products. Vulcanization by sulfur alone is believed to be primarily via a thermally induced free-radical reaction. The sulfur will slowly react allylic to the site of unsaturation to form polysulfide substituents. These then are subject to... 

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