Stereochemistry of the four diastereoisomeric 1,2,5-trimethyl-4-phenylpiperidines

Abstract

Four isomeric 1,2,5-trimethyl-4-phenylpiperidines have been obtained from appropriate alcohols by dehydration–catalytic hydrogenation or hydrogenolysis. Their ¹³C and ¹H n.m.r. spectra are interpreted in terms of preferred chair conformations with configurations c-2-Me, c-5-Me, r-4-Ph (δ); t-2-Me, c-5-Me, r-4-Ph (β); c-2-Me, t-5-Me, r-4-Ph (γ); and t-2-Me, t-5-Me, r-4-Ph (α) for these isomers. Evidence for isomerization during catalytic hydrogenation of the binary mixture of alkenes obtained on dehydration of γ-1,2,5-trimethyl-4-phenylpiperidin-4-ol is presented