Diastereoselective Syntheses of (3<i>R*</i>,4<i>R*</i>)- and (3<i>R*</i>,4<i>S*</i>)‑4-Aryl-3-methyl-4-piperidinemethanol and Fluoro Analogues

Two concise and high-yielding diastereoselective syntheses of 4-aryl-3-methyl-4-piperidinemethanols were realized from 1,3-dimethyl-4-piperidinone. The key reactions to control the C3–C4 relative stereochemistry were the alkoxymethylation of a metalloenamine generated from 4-aryl-3-methyl-1,2,3,6-tetrahydropyridine that afforded the (3R*,4S*)-form and the nucleophilic substitution of a fluoroarene with deprotonated 3-methyl-4-piperidinenitrile giving the (3R*,4R*)-isomer. The corresponding fluoromethyl analogues were subsequently obtained through the fluorination of the piperidinemethanols using DAST.