Ring opening of thiiranes

Acid-catalyzed ring opening of thiirane oxides.423... 

The analogous ring-opening of thiiranes with acyl chlorides produces S-(p-chloroethyl) thiocarboxylates [33]. 

Hoz and co-workers used the Markus equation and theory at the HF/6-31G level to determine that the strain relief contribution to ring opening of thiirane by MeS is 8.5kcalmol <2001JOC915>. There is an additional contribution to the lowering of the activation energy, relative to that for the unstrained model (MeS -I- MeSMe) of 13.3 kcal mol . The additional factor was not identified. 

Whereas epoxides are readily cleaved by ammonia and amines (6), ring opening of thiiranes is rather sluggish. The situation is ameliorated by adding silver ion (7) to coordinate with the sulfur atom which then renders the ring C-S bond more permanently polarized (and hence less polarizable), i.e., the ring carbon becomes harder and more responsive to hard bases. Precedence for this activation is found in a one-step synthesis of sulfenamides from disulfides (8). 

Examples of previously described methods are the ring-opening of thiirans [ethylene sulphide with Pr"ONa and H2C=CHCH2C1 Pr"0(CH2CH2S) -CH2CH=CH2 (n = 1 or 2)], the use of a chlorosulphonium salt (RC02 Et3NH+... 

The ring opening of thiiranes with an emphasis on the regiospecificity of the ringopening reaction with different nucleophiles and on the effect of such nucleophiles on the 5n reactions, alkene formation, and polymerization reactions, has been reviewed. 

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