DURING continued investigations of structure-activity relationships in synthetic analgesics, some compounds related to the reversed esters of pethidine, namely isomers of N-(2’-phenylethyl)-2-methyl-4-phenyl-4piperidinol, N-(2‘-phenylethyl)-2,6-dimethyl-4-phenyl-4-piperidinol, cis2,6-dimethyl-4-phenyl-4-piperidinol and some of their esters were prepared by routes involving the addition of lithium phenyl to the appropriate ketone. These compounds are of interest in view of the recent introduction by the Russians of the potent analgesic Promedo1112. Treatment of N-(2’-phenylethyl)-2-methyl-4-piperidone (I) with lithium phenyl gave two isomeric piperidinols (Type A and B) which were separated by fractional crystallisation of the hydrochlorides. These isomers A and B (I1 and 111) obtained in a ratio of 2: 1 were assigned cis-CH,/C,H, and trans-CH,/C,H, configurations respectively on the basis of the following evidence. (a) The steric course of addition of organometallic derivatives to ketones is controlled by steric hindrance involved in the approach to the carbon atom of the carbonyl group, and by an energy factor which influences the ease with which a group may be forced into an unfavoured position3. With N-(2’-phenylethyl)-2-methyl-4-piperidone, attack from side “b” is sterically hindered, and causes a preferential formation of the type A isomer (11), with an equatorial phenyl group.