Conformational analysis and stereochemistry of the reduction of 2-alkoxymethyl-4-oxopiperidines
The isomer with an axially oriented alkoxymethyl group predominates in the equilibrium mixture of 1-aklyl-2,5-dimethyl-2-alkoxymethyl-4-piperidones investigated under both alkaline and acidic equilibrium conditions, and its percentage increases as the volume of the alkoxy group increases in the order Me, Et, iso-Pr. The reduction of 4-ketopiperidines that contain a polar function in the 2 position follows the same principles as those that obtain when it is absent, i.e., exclusively the equatorial alcohols are obtained in the case of reduction with lithium and ethanol in liquid ammonia, whereas primarily the axial alcohols are obtained in the case of reduction with sodium borohydride. The selectivity of the reduction increases on passing from the free bases to the hydrochlorides.
KeywordsAlcohol Ammonia Lithium Hydrochloride Equilibrium Condition
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