Starting from benzyl 3,5-di-O-benzyl-2-deoxy-1,4-dithio-D-erythro- pentofuranoside (4), the following 2'-deoxy nucleoside analogues have been synthesized: 4'-thiothymidine (8), 3'-azido-4'-thio- deoxythymidine (10), and (E)-5-(2-bromovinyl)-4'-thio-2'-deoxyuridine (22). The first compound is toxic, the second is not toxic nor has detectable biological activity, and the third is not toxic and has significant activity against some herpesviruses.
Trifluorovinyllithium has been synthesised in high yield from 1,1,1,2-tetrafluoroethane (HFC 134a) by treatment with butyllithium at -78 "C, and then treated with a variety of electrophiles in one-pot reactions.
The formation of lithio derivatives from fluorinated benzenes and fluorinated bromobenzenes has been studied. The bases used were lithium diisopropylamide (LDA) in THF-hexane, butyllithium in diethyl etherhexane and butyllithium in THF-hexane. The lithiated intermediates have been trapped using acetone, to form fluorinated 2-arylpropan-2-ols, or have been warmed to produce benzynes which have been trapped by furan in Diels-Alder additions. The use of LDA allows clean removal of the most acidic proton in the aromatic ring: butyllithium in ether-hexane kings about clean bromine-lithium exchange. In contrast, the use of butyllithium in THF-hexane at -78 "C results in autometallation and the formation of more complex product mixtures. For the formation of the benzynes involved in the Diels-Alder reactions it is necessary to warm the reaction mixtures. When ether-hexane is used as solvent the reactions remain fairly clean, but when THF is added the increasing autometallation again results in more complex reaction mixtures.
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