Menthyl crotonate

Following this concept, the 1,4-addition of phenylmagnesium bromide to (-)-menthyl crotonate was investigated, however with quite disappointing results.7 By using sugar-derived chiral auxiliaries, some-... 

P, P ] Inouye and co-workers documented that the addition of the morpholine enamine of cyclohexanone to ( —)-menthyl crotonate proceeds with detectable asymmetric induction (Scheme 10) (21). Although the level of face selection was not determined, degradation indicated that the S enantiomer is the preferred product. 

Related Reagents. 8-Phenylmenthyl Crotonate 8-Phenyl-menthyl Glyoxylate 8-Phenylmenthyl Pyruvate. 

The influence of 7C-stacking on the conformation of substrates and transition states has been a matter of debate [44, 46-49] (see above). Nonetheless, the efficiency of 8-phenylsubstituted menthyl or /ra s-2-phenylsubstituted cyclohexyl esters of a,p-unsaturated acids as substrates in asymmetric induction has been ascribed to such effects [66], Both NMR spectroscopy and calculations [67, 68] have shown that 7c-stacking can stabilize the s-cis-syn conformation of crotonates 10, especially when Ar = 2-Np or 4-PhOCgH4. An X-ray determination shows that 10 (Ar = 2-Np) adopts the s-cis conformation in the solid state [67], Interactions with remote substituents of the substrate can cause a preferred reactive conformation to intervene. For example, the reduction of y-ketoboronates by borane is highly stereoselective and probably takes place via an internal complexed intermediate 11, even though tins could not be characterized in the ground state [69, 70]. 

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