Cinnamyl selenides, asymmetric oxidation

The asymmetric oxidation of sulphides to chiral sulphoxides with t-butyl hydroperoxide is catalysed very effectively by a titanium complex, produced in situ from a titanium alkoxide and a chiral binaphthol, with enantioselectivities up to 96%342. The Sharpless oxidation of aryl cinnamyl selenides 217 gave a chiral 1-phenyl-2-propen-l-ol (218) via an asymmetric [2,3] sigmatropic shift (Scheme 4)343. For other titanium-catalysed epoxidations, see Section V.D.l on vanadium catalysis. 

More recently, Uemura and co-workers have carried out the asymmetric oxidation of several aryl cinnamyl selenides using Sharpless oxidants [26] (Scheme 15). Typical results are shown in Table 6. They showed a strong corre-... 

Table 6. Asymmetric oxidation of aryl cinnamyl selenides using the Sharpless oxidant...

The asymmetric [2,3]sigmatropic rearrangement of several other allyl aryl selenides has been reported, but only moderate selectivities are observed [27] (Scheme 18). The oxidation of cinnamyl and geranyl selenides derived from L-prolinol with MCPBA at -90°C afforded the chiral l-phenyl-2-propen-l-ol and linalool with moderate enantiomeric excess, respectively. 

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