Frans-l-Phenylpropene

Enantioselective osmylotion of alkenes. Osmium tetroxide forms a 1 1 wine-red complex with the chiral diamine l2 that effects efficient enantioselective dihy-droxylation of monosubstituted, oww-disubstituted, and trisubstituted alkenes (83-99% ee) at -110° in THF. The enantioface differentiation in all cases corresponds to that observed with t/mr-3-hexene and the complex with (-)-l. Essentially complete asymmetric induction is observed with frans-l-phenylpropene (99% ee). 

As intriguing as the above is the fact that an optically active phase-transfer catalyst can induce asymmetry. Addition of dichlorocarbene to styrene in the presence of (62) results in a cyclopropane product with a rotation of 3.18 (Scheme 8). On removing the hydroxy-group and employing optically active (63) for the same addition, the optical purity of the product is dramatically reduced. Analogous results are obtained with frans-l-phenylpropene. Although the degree of asymmetric induction is low,... 

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