Stereoselective synthesis of substituted cyclohexanone cyanohydrins

Substituted 1-hydroxy cyclohexane-1-carboxyhc acids, which could be prepared from the corresponding cyanohydrins by acid hydrolysis as described above, are important as pharmaceuticals and plant-protective agents. Although the compounds derived from 2- and 3-cyclohexanones have two stereogenic centers, stereoselective syntheses of these interesting products have been published only very recently. Completely unexpected are the results of HNL-catalyzed additions to 4-substituted cyclohexanones, which do not possess a prochiral center. The (R)-PaHNL-catalyzed addition affords almost exclusively fran -isomers, whereas with (5 )-MeHNL cA-addition is favored (Table 4).  

While the chemical addition of HCN to 4-(2-propenyl)cyclohexanone affords a cis/trans ratio of 13 82, the MeHNL-catalyzed addition gives almost exclusively the c 5-isomer ( 96%). The chemoenzymatic syntheses of rengyol and isorengyol are other examples for applications of HNL-catalyzed additions of HCN to cyclohexanones.  

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