Sharpless asymmetric 3, 3 sigmatropic

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. 

Asymmetric [2,3]sigmatropic rearrangements can proceed via optically active selenoxides. It has been shown that the Davis oxidant 158 can be used for the oxidation of selenides such as 172. The reaction product, after oxidation and rearrangement, is the allylic alcohol 173 formed with 35% ee (Scheme 50).279,282 Also Sharpless conditions (Ti(/ -PrO)4, (+)-DIPT, /-BuOOH) have been applied to this reaction and the product has been obtained in 69% ee. When, however, the phenyl selenide moiety in 172 is replaced with an or/ < -nitrophenyl selenide, the selectivity is increased to 92% ee in the allylic alcohol 173 using Sharpless conditions.296 Other selenides such as 2 -pyridyl or ferrocenyl selenides gave much lower selectivities. 

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