The Dimroth rearrangement. Part XVI. A new general synthesis and rearrangement of C-alkylated 1,6-dihydro-6-imino-1-methylpyrimidines
A new primary synthesis of 1,6-dihydro-6-imino-1-methylpyrimidine (3a) and its 2-,4-, and/or 5-alkylated derivatives (3c–o) is described: a 3-aminoacrylonitrile (1) is converted by an orthoester into its 3-ethoxyalkylidene-amino-analogue (2) which undergoes methylaminolysis and subsequent cyclization to the required imine (3); a similar route gives the bicyclic imines (6; n= 3 or 4). All the imines rearrange in alkaline media to the corresponding 6(4)-methylaminopyrimidines [(4) or (7)], but at widely differing rates which depend on the position, type, and number of C-alkyl substituents. The rearrangement rates, ionization constants, and some mass spectra are discussed.