Asymmetric aryl propenes

Jacobsen and co-workers14 have shown that a tridentate Schiff base chromium complex 13 catalyzed an asymmetric carbonyl-ene reaction between a variety of aryl aldehydes (14, Equation (8)) and 2-methoxy propene 15 or 2-trimethylsiloxypropene. The highest yields were afforded when the aryl ring was substituted with an electron-withdrawing group however, the substituent did not seem to affect the enantioselectivity. 

Cpsymmetric organolanthanide complexes exhibit moderate to good enantioselectivities in the hydrogenation and deuteration of styrene and 2-phenyl-1-butene.433 Cationic iridium-phosphanodihydrooxazole complexes are more efficient catalysts for the asymmetric hydrogenation of unfunctionalized aryl-substituted alkenes. The best catalyst (42) gives high yield (>99%) and excellent enantioselectivity (97% ee) in the hydrogenation of ( )-l,2-diphenyl-l-propene 434... 

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. 

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. 

Ma et al. reported the asymmetric bromohydroiq lation of 2-aryl-2-propen-1-ols with N-bromosuccinimide (NBS). Regio- and enantioselectivity were achieved by using a boronate ester as a tether and quinine-derived sulfonamide catalysts 5. Products were obtained in up to 90% yield and with 96% ee (Scheme 15.35). 

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