A selective synthesis of 3,6-dihydro-7H-1,2,3-triazolo[4,5-d]pyrimidin-7- ones

The carbodiimides 2, obtained from aza-Wittig reactions of iminophosphorane 1 with aromatic isocyanates, reacted with primary amine RNH2 (R ≠ H, Me) to produce isolable guanidine intermediates 3, which were further treated with sodium ethoxide in a mixed solvent to give selectivly one of the regioisomer 4 via a base catalytic cyclization mechanism. However, another regioisomers 5 were obtained directly as RNH2 (R = H, Me) were used in the absence of sodium ethoxide, via a direct cyclization mechanism. Copyright © 2005 The Chemical Society of Japan.link_to_subscribed_fulltex