Enaminone-Based Synthesis of Dipodazine Derivatives

A series of racemic dipodazine analogues 9 were prepared in 22–80% yield from (3Z,6RS)-3-[(dimethylamino)methylidene]-6-methyl-1-(phenylmethyl)piperazine-2,5-dione (7) (Scheme 1), which was prepared in four steps from (RS)-alanine methyl ester hydrochloride. The preparation of nonracemic 7 from (S)-alanine methyl ester hydrochloride failed, since the introduction of the enamino functionality at position 3 of the precursor 6 was accompanied by almost complete racemization.