The carbodiimides 4, obtained from aza-Wittig reactions of iminophosphorane 3 with aromatic isocyanates, reacted with secondary amines, phenols or alcohols in the presence of catalytic amounts of K2CO3 or sodium alkoxide to give 2-substituted benzofuro[3,2-d]pyrimidin-4(3H)-ones 6. However, when 2,2′-iminobis[ethanol] was used, the unexpected ring opening product 7 was formed instead of 6. Reaction of 4 with primary amines RNH2 (R = Et, Pr, Bu, etc.) gave guanidine intermediates 8, which were further treated with EtONa to give only one regioisomer 9 via a base catalyzed cyclization. Howe...
