The Independent Isolation of a Primary Enamine and the Tautomeric Imine

Abstract Isolation of a primary enamine and its tautomeric imine has been described and their dimerization discussed. Reduction of ethyl 3-methyl-2-nitro-2-butenoate with aluminum amalgam afforded ethyl 2-amino-3-methyl-2-butenoate (I) (enamine form), while treatment of ethyl 3-methyl-2-oxobutanoate with triphenylphosphinimine gave ethyl 2-imino-3-methylbutanoate (II) (imino form). The enamine and its tautomeric imine dimerized to give 3,6-diisopropylidene-2,5-dioxopiperazine (VII) and 2-ethoxycarbonyl-2,5-diisopropylimidazolid-4-one (IX), respectively. However, individual acylation of both the enamine and the imine gave the same acyl compound.