Edda Sandri

Alkyllithium-promoted ring fissions of halides derived from 1,4:3,6-dianhydrohexitols

Abstract Halogen-substituted 2,6-dioxabicyclo[3.3.0]octanes, readily obtained from 1,4:3,6-dianhydro-D-mannitol may be useful sources of highly functionalized homochiral synthons. Treated with an alkyllithium the title compounds undergo dehalogenative (X = I) or nondehalogenative ring fission (X = Cl) giving homochiral 2,5-dihydrofurans or 2-(1-halogenovinyl)tetrahydrofurans, respectively. The two elimination processes compete comparably for X = Br.

Kinetic versus thermodynamic acidity of α-sulphonium protons

Abstract The kinetic acidity of structurally different, or stereochemically different, protons α to a sulphonium function may not parallel their thermodynamic acidity.

cis- and trans-Doubly bridged ethylenes via sigmatropic rearrangements. Synthesis of Cs- and C1-(±)-15-thiabicyclo[10.7.0]nonadec-1(12)-ene

cis- and trans-Doubly bridged ethylenes result from the stereospecific [2,3]sigmatropic rearrangement of spirocyclic allylic sulphonium ylides.

Stereospecific intramolecular addition of α-lithio sulphoxides or sulphones to inactivated double bonds

Treatment of the l-oxides or l,l-dioxides of trans homoallylic 8–10 membered ring cyclic sulphides with BuLi in tetrahydrofuran result in transsnnular addition of the α-thio carbanion to the E double bond with formation of bicyclic products.

Acid catalysis in the intramolecular addition of α-lithiosulphoxides to isolated double bonds

Intramolecular addition of a α-sulphinyl carbanion to an isolated double bond is observed with mesocyclic metallated E homoallylic sulphoxides (1) and (2); kinetic data suggest that this process is acid catalysed and that free (1) is the proton donor species.