6-Alkyl derivatives of 3-(3,4-dihydroxyphenyl)alanine (dopa). Part I. Synthesis via oxazolinones

Abstract

3-(3,4-Dihydroxyphenyl)alanines with a methyl, ethyl, or isopropyl group in the 6-position were obtained via the corresponding oxazolinones by an Erlenmeyer–Plöchl procedure. In the synthesis of 6-t-butyldopa (27) the intermediate α-benzamido-4,5-dimethoxy-2-t-butylcinnamic acid (21) was obtained in reasonable yield by treatment of the Grignard reagent from 5-t-butyl-4-bromoveratrole (11) with 4-ethoxymethylene-2-phenyl-Δ²-oxazolin-5-one (18). The protecting groups (N-benzoyl and O-methyl) could be removed from the hydrogenated α-benzamidocinnamic acid without affecting the t-butyl group.