Abstract
Lithiation of the sulfones 1–3 in THF at −78° with lithium diisopropyl amide (LDA) is regioselective, since deuteration of the α-lithiosulfone 4 results in formation of the α-monodeuteriated sulfone 7. Higher temperature causes an intramolecular 1,4-addition of the lithiated sulfone 4 to the lithiated cyclic sulfone 19 and an intermolecular 1,4-addition of the lithiated sulfones 5 and 6. The cyclisation of Z-sulfone 1 has been used for the isolation of the isomeric E-sulfone 2 from mixtures of 1 and 2. The lithiated sulfones 4–6 are chlorinated with hexachloroethane (HCE). Due to acid/base reactions the α,α-dichlorinated cyclic sulfone 23 and α,α'-dichlorinated butadienyl sulfones 13–15 are formed in small amounts.
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