A new efficient synthesis of 2,5,6-trisubstituted oxazolo[5,4-d]pyrimidi-7(6H)-ones by consecutive aza-Wittig reaction was developed. The sequential three-component reaction of oxazolyliminophosphorane 4, isocyanates and amines produced 2,5,6-trisubstituted oxazolo[5,4-d]pyrimidi-7(6H)-ones 7 in good overall yields in the presence of catalyti...