Lithiated sulfoximines

Stabilized lithiated sulfoximines (112) undergo highly diastereoselective Michael additions to cyclic enones at —78 °C under kmetically controlled conditions. At room temperature, the initially formed adducts (113) undergo intramolecular substitution of the sulfonimidoyl group, with inversion of configuration to afford the corresponding cyclopropanes (114).92... 

The X-ray crystal structures of lithiated sulfoximines were reported in 1986/87 by Gais. Lithiated (S)-lV,S-dimethyl-S-phenylsulfoximine crystallized as its tetra-methylethylenediamine (tmeda) complex as a chiral tetramer of structure [(S)-N-methyl-5-phenylsulfonimidoyl)methyllithium]4-2(tmeda) with approximately C2 symmetry.41 Two of the lithium cations of the tetramer were coordinated to a tmeda molecule and the O atoms of two different carbanionic species. The other two lithium cations were found to be coordinated to the N atoms of three different sulfonimidoyl carbanionic species and to one C atom (the a-carbon) of each of these carbanionic species. These lithium cations were thus found to form four-mem-bered chelate rings involving the atoms, Li-Ca-S-N. A later study was successful... 

Treatment of lithiated sulfoximines 48a and 49 with N-benzylideneaniline BF3 complex gave the desired adducts with only moderate to good diastereoselectivity (Table 8).49 The lithiated sulfoximine 49 failed to give adducts with other acyclic imines even when the imines were precomplexed with BF3 etherate. This is possibly a consequence of the increased steric demand and the resonance stabilizing effect of the 5-phenyl group of 49. 

The reactions of lithiated sulfoximines 143 with cyclic enones give mixtures of regio- and diastereoisomers. The regioselectivity is dependent on the nature of the A-substituent on sulfur.59,75,81 A-Tosyl derivatives give exclusively a-1,4-addition products (144), while this type of adduct is slightly favored in the case of A-phenyl derivatives. A-terf-Butyl-diphenylsilyl (TBDPS) derivatives, however, favor y-1,4-adducts (145). In all cases the adducts were formed as mixtures of diastereoisomers except in the case of the y-1,4-adducts 145 (n = 1, Ar = Tol, R = Ph) which were obtained in low yield as a single diastereoisomer.75... 

In the original publication lithiated sulfoximines should have been referred to as lithiated (S)-sulfoxi mines and not (R)-lithiated sulfoximines. 

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