Allylic selenimides rearrangement

The enantioselective [2,3]sigmatropic rearrangement of allylic selenimides has been achieved by application of the asymmetric synthesis of selenimides [35]. When this reaction was applied to various aryl cinnamyl selenides, the expected optically active allylic amines were obtained in good yield with moderate enan-tioselectivity via [2,3]sigmatropic rearrangement of the intermediate chiral allylic selenimides (Scheme 25). 

Chiral a-alkyha-vinyl amino acids have been prepared with high levels of enantiomeric purity by [2,3]-sigmatropic rearrangement of allylic selenimides (Scheme 16). ... 

Nitrene transfer to selenide is also possible. Catalytic asymmetric induction in this process has been studied with Cu(OTf)/bis(oxazoline) catalyst (Scheme 22). When prochiral selenide 206 and TsN=IPh are allowed to react in the presence of Cu(OTf)/chiral bis(oxazoline) 122b, selenimide 207 is obtained with enantioselectivity of 20-36% ee. When arylcinnamyl selenide 208 is applied to this reaction, corresponding selenimide 209 is produced which undergoes [2,3]-sigmatropic rearrangement to afford chiral allylic amides 211 in up to 30% ee. 

Asymmetric selenoxide elimination of the optically active vinyl selenoxides affords optically active allenes and cyclohexylidenes. On the other hand, asymmetric [2,3]sigmatropic rearrangement of allylic selenoxides, selenimides, and selenium ylides leads to the formation of the corresponding optically active allylic alcohols, amines, and homoallylic selenides, respectively. 

Sulfides can be oxidized to sulfoxides by reaction with NCS in methanol (0°C, 1 h). Similarly, selenides couple with amines when activated by NCS to form selenimide species. These have been generated from allylic selenides in order to prepare allylic amines and chiral secondary allylic carbamates by [2,3]-sigmatropic rearrangement (eq 8). ... 

DFT has been used to model the endo and exo transition states for [2,3]-sigmatropic rearrangement of allylic aryl-selenoxides and -selenimides. °... 

Catalytic Nitrene Transfer to Heteroatoms. The experimental procedure described above for the copper-catalyzed aziridination of olefins can be applied to the imidation of sulfides, where CuOTf in conjunction with PhI=NTs mediates the formation of siilfimides in good yields (eq 95). Spontaneous [2,3] sigma-tropic rearrangements occur in the case of allylic sulfides. Chiral bis(oxazoline)-CuOTf complexes catalyze both reactions with acceptable enantioselectivities (eq 96). Chloratnine-T is also a suitable but less efficient nitrene precursor. Selenides undergo the same catalytic asymmetric imidation to afford selenimides albeit with lower yields and enantioselectivities. ... 

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