Thiiranes 1,4-hydrogen shift

The chemical shifts of the H-methyl groups in thiiranes 31a, 31b and 31c were found to be = 1.59,1.44 and 1.45, respectively. The chemical shifts of the -anti-methyl hydrogens (i.e. those of R ) where found to be (5 = 1.25,1.23 and 1.27 in 32a-c compared with <5= 1.74 and 1.64 for syn-R -hydrogens in 32a and 31c, respectively . The consistency of the deshielding effect in accordance with the position of the -hydrogens in ring sulfoxides is thus apparent. These observations validate the applicability of the S—O anisotropy rule to the three-membered ring system. 

Similar reactions were carried out on 17,29 18,30 and 19.30 The last gave thiochromans and 2,3-dihydrothiophenes from an apparent cyclization at the ortho methyl substituent, but in fact involving a variety of hydrogen and methyl shifts. The route to the two main products [Eq. (7)] of the thio-Claisen rearrangement has been suggested to be via the thiirane intermediate (20).31... 

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